Sherif F. Nagueh, MD, FACC, FAHA

• Professor of Medicine
• Department of Cardiology
• Weill Cornell Medical College
• Associate Director, Echocardiography Laboratory
• Methodist DeBakey Heart and Vascular Center
• The Methodist Hospital
• Houston, Texas

The duration of each bout of the disease varied from a week to a few months high cholesterol levels definition generic crestor 20 mg buy on-line, and 69% of the patients had recurrences of the symptoms cholesterol kidney stones purchase 5 mg crestor with amex. Not knowing at the time the etiology of the disease cholesterol test machine crestor 20 mg otc, the investigators could not determine another important time characteristic cholesterol test clinic purchase crestor on line, the incubation period cholesterol ratio and triglycerides discount crestor 5 mg online, or the interval from exposure to the first onset of symptoms. Place characteristics are primarily the site of residence and the area in which the patients lived. The Connecticut cases were concentrated in three adjacent towns on the eastern side of the Connecticut River. Personal characteristics include the age and sex of the patients and any possible genetic predisposition to the disease. Using the information they gathered on time, place, and personal characteristics, the epidemiologists listed the cases by times of onset and constructed what is called an epidemic curve. They dubbed the outbreak Lyme arthritis, although that name was later modified to Lyme disease. Was the outbreak a surveillance artifact resulting from the many questions about arthritis that were being asked by outsiders The simplest way to assess that possibility was to go elsewhere and ask the same questions. By surveying towns on the other side of the Connecticut River, the investigators determined that increased interest did not result in an increase in the number of cases of arthritis reported. In their early investigation, the epidemiologists wondered how common Lyme disease might be. Assessing the attack rate of an epidemic disease requires knowing the total number of cases (the numerator) and the total number of people who are "at risk" (the denominator). In the context of many confined outbreaks, it is possible to make that calculation. For example, if Chapter 59: Principles of Epidemiology 589 25 of 125 guests who attended a wedding later developed staphylococcal food poisoning from eating the potato salad, the attack rate is 20%. In the first Lyme disease investigation, neither the total number of cases nor the number of at-risk persons was known. However, surveillance for the infection in subsequent years has yielded case reports from each state that can be used to calculate the local risk of Lyme disease in the United States. Those data can be reported as an incidence (the number of cases during a defined time period divided by the population of the state during that time) or as a prevalence (the total number of cases at any given time). For example, we now know that the annual incidence of Lyme disease in Connecticut (from 1992 to 1998) was 68 per 100,000 population, whereas in neighboring Massachusetts, the annual incidence was only 5 per 100,000 population, an almost 12-fold lower risk. Nonetheless, the clustering of cases in the summer or early fall, and most patients living in wooded areas along lakes or streams, suggested transmission through a vector such as an insect or tick. Others, like a ruptured appendix, urinary tract infections, or osteomyelitis, are not. To answer that question, the investigators attempted to trace contacts; but even in families with several affected members, the onset of illness had usually taken place in different years. About one-quarter of the patients had reported that the symptoms of arthritis were preceded by an unusual skin rash. An astute dermatology consultant remembered that similar rashes had been described in 1910 in Sweden and had been attributed to tick bites. The investigators undertook a case­control study in 1977, in which the cases are matched with a similar group of control or unaffected persons. Note that case­ control studies are always retrospective; that is, they begin by defining groups of ill or well subjects and then look to the past for potential exposures or risk factors that were more common among the ill than the well subjects. After matching for age, sex, and any other relevant factors, the epidemiologists found that those affected by Lyme disease were more likely to live in households with pets and thus were more likely to come in contact with the ticks that dogs and cats picked up in the woods of that region. In a roundabout way, that clue became more credible when the investigators remembered the suggestive clinical finding of the Swedish researchers. So far, the connection between the rash and Lyme disease depended on retrospective evidence, which is subject to more bias because it depends on collecting exposure data from people who already know they are ill. To make the connection stronger, it became appropriate to ask if patients with the signs of erythema chronicum migrans progressed to develop Lyme disease. In 1977, the team set up a prospective study, looking for patients with the rash and observing them prospectively for some time. That type of study is referred to as a cohort study since the individuals included in the cohort have specific characteristics in common but have not yet developed the disease of interest. In contrast to the case­control approach, a cohort study defines subjects by their clinical characteristics and exposures and then follows the subjects to determine who becomes ill and who remains well. In the Connecticut study, 19 of 32 new cases of erythema chronicum migrans progressed to Lyme disease. Meanwhile, the "tick connection" became even more plausible after a thorough entomological survey. After collecting insects and ticks from Lyme and the surrounding areas, the investigators found that adult ticks were 16 times more abundant on the east side of the Connecticut River than on the west side. That finding corresponded roughly to the incidence of cases of Lyme disease in the two areas. In addition, many more tick bites were reported by the arthritis patients than by their neighbors without the disease. At the same time, a surveillance network had been set up in Connecticut and parts of the adjacent states to gather information about other cases. A careful study revealed that, contrary to the early reports, the disease was more frequent in adults than in children. Many arthritis patients had serious manifestations, such as neurological dysfunction and myocarditis. Thus, the disease turned out to be considerably more complex than described by the original case definition. That illustrates an important epidemiological point: an early case definition is, by necessity, tentative and may be modified when the full spectrum of the disease becomes known. Search for the Etiological Agent So far, the investigators hypothesized that Lyme disease was an infection, most likely transmitted by ticks. Despite many attempts, no laboratory had succeeded in 590 Part 3: Pathophysiology of Infectious Diseases isolating a virus, which at the time seemed to be a good candidate for being the agent of the disease. On the other hand, the investigators collected anecdotal evidence that tetracycline, erythromycin, and penicillin were clinically effective. With time, more physicians reported the beneficial effects of antibiotics, making a bacterial etiology more likely. At about that time, in 1979 and 1980, entomologists and microbiologists at the Rocky Mountain Public Health Laboratory in Montana, who were experts in tickborne diseases, examined ticks sent from the affected area and found that the gut of many specimens contained unusual spirochetes. Using a culture medium that supports the growth of tickborne or louseborne spirochetes, the microbiologists succeeded in growing a newly recognized spirochete. Soon thereafter they isolated the spirochete from human cases, and the immune responses of patients were linked to that organism. The spirochete was classified in the Borrelia genus, a group that includes the agent of another tickborne disease also found in the United States, relapsing fever. Once the organism was identified, a diagnostic test of exposure to the infection was developed. Investigators in many parts of the world could carry out serological surveys, or serosurveys, to determine the proportion of persons with antibodies to B. In general, serosurveys enable investigators to recognize a wide range of clinical manifestations, from asymptomatic cases to fullblown disease. That recognition is important because in most infectious diseases, there are many more asymptomatic than clinically overt cases. The use of serosurveys has led to diagnoses of Lyme disease in other parts of the United States, especially on both coasts, as well as in Canada, Europe, Asia, and Australia. It is considered a serious disease, mainly because of its important and chronic neurological manifestations. Reducing the overabundant deer population through authorized deer hunting has been a controversial means of indirectly controlling B. A few years after the original phone calls, a new disease was described, its agent and mode of transmission were identified, and preventive and therapeutic measures had been instituted. Note that it took the joint efforts of epidemiologists, clinicians, entomologists, microbiologists, and alert and determined members of the public. These principles include the routes of transmission, incubation periods, communicability, and individual susceptibility. Transmission from human to human may take place from parent to offspring or between mature individuals. Vertical transmission refers to the passage of an agent from an infected mother to her fetus or infant. A newborn can also pick up chlamydiae, gonococci, cytomegalovirus, or hepatitis B virus during passage through the birth canal. Horizontal transmission can be among individuals in close proximity and involves sexual intercourse, handto-hand contact, and spread via droplet or aerosol. Thus, bacteria or viruses that infect the respiratory tract are often expelled as aerosols during coughing and even talking, and may be inhaled by bystanders. If the organism is resistant to drying, as is the case with the tubercle bacillus, the danger of inhalation can persist for a long time. Intestinal pathogens often cause diarrhea, which increases their distribution in the environment through oral­fecal contact and, under conditions of poor sanitation, results in contaminated drinking water and foodstuffs. Some diseases are acquired by breaching the skin or mucous membranes by trauma, insect bites, blood transfusions, or contaminated hypodermic needles. Many of the agents that are transmitted by insect vectors have different life cycles in the vector and in the host. Note that some of these organisms may be transmitted by more than one of these routes. Prevention Strategies After the agent was confirmed, investigators set about attempting to develop a vaccine against disease. That process was complicated and required knowledge of the immunology of infection and the role of the outer membrane proteins of B. As with many infectious agents, a vaccine would be one way to prevent future cases of Lyme disease. In fact, a vaccine against the disease was developed and was shown to be effective, but manufacturers have stopped development because of concern about the potential risk of arthritis resulting from vaccine administration. Transmission from the animal may be direct, as in the bite from a rabid dog, or through insect vectors, as in the plague or the viral encephalitides. Lyme disease is another zoonosis; its natural reservoir is mice, and the infection is transmitted to humans by a tick that feeds on mice, deer, and a variety of other mammalian hosts. Indirect transmission can result from contact with a contaminated environment, such as with rodent excreta in the hantavirus outbreak in the southwestern United States. In other diseases, the reservoir is the inanimate environment and the organisms live freely in nature. For example, Clostridium tetani, the bacteria that causes tetanus, can be found in soil and is encountered whenever dirt enters a deep wound. In addition, humans or animals can contribute to the frequency with which the agents are found in nature. The cholera bacilli grow naturally in warm estuaries, probably on the surface of shellfish, but contamination from human feces can help the organisms become established in a previously unaffected area. For example, a large infective dose can shorten it, and a small one can lengthen it. To epidemiologists, the incubation period is particularly important because some diseases can be transmitted from asymptomatic patients during that time. Control of transmission may therefore rely on special surveillance methods that include infected but asymptomatic persons. For example, the incubation period in hepatitis A usually ranges from 2 to 6 weeks. However, individuals can transmit the virus for only 1 or 2 weeks before the onset of the disease. The period of communicability may extend long after the disease symptoms abate, as in the case of a chronic carrier. For example, hepatitis B carriers can usually transmit the virus for the length of time they carry it. Many of the preceding chapters have discussed the carrier state at some length (see Chapters 14, 17, 27, 38, 41, and 42). One of the most intensively studied genetic effects is the decreased susceptibility to malaria of persons with the sickle cell trait (see Chapter 52). It is also well established that nonwhites are more prone to the disseminated form of the fungal disease coccidioidomycosis than are whites. To safeguard both the public interest and individual rights to privacy, a considerable body of local and national laws has been developed in most countries of the world. For instance, in the United States, certain communicable diseases are notifiable; that is, physicians are obliged to report cases to the U. Typically this is accomplished through case-report forms that are collected and monitored by a local health department. In addition, each state has its own surveillance mechanism and reporting requirements for the study of communicable diseases within its borders. Each has a state board of health and a reference laboratory equipped to carry out special diagnostic tests that are often outside the scope of hospital laboratories. Of course, most outbreak investigations and the discovery of new infectious agents usually start at the bedside of an individual patient and physician. It is therefore crucial for practicing clinicians to be aware of reporting requirements and state laboratory support resources and to remain ever alert for the next new outbreak. For instance, some individuals seem more prone to respiratory or intestinal infections than are most people. Often, the reason for this variability is unknown or related to the subtle and complex genetic variability that makes us each a unique individual with a unique immune system. However, there are several specific immunodeficiencies of which the clinician should be aware, as they may portend specific patterns of risk for infection. When the immune deficiency becomes more severe and the risks more evident, the specific etiology is often easier to ascertain. Epidemiologists must be aware of the various susceptibilities of members of the general population.

Syndromes

• Wound care for areas of skin with blood clots
• Bloating or swollen belly area
• Headache
• Mood swings with periods of crying
• Eye problems
• Repeated ear infections
• Have diabetes, premenstrual syndrome, an underactive thyroid, or rheumatoid arthritis.
• Café-au-lait spots are light tan, the color of coffee with milk. They often appear at birth, or may develop within the first few years. Children who have many of these spots, or large spots, may be more likely to have a condition called neurofibromatosis.
• Have dental problems corrected

Some pathogenic bacteria remain in chronic association with the host cholesterol test kit price buy on line crestor, often with limited host response that is insufficient for clearing the infection cholesterol in shrimp hdl or ldl buy cheap crestor on line. An important example is Helicobacter pylori cholesterol levels meat buy cheap crestor online, which causes gastric ulcers and probably is responsible for gastric adenocarcinomas (see Chapter 22) cholesterol levels explained order genuine crestor line. Proteolysis of Antibodies Certain bacteria-gonococci cholesterol test questions generic 5 mg crestor mastercard, meningococci, and Haemophilus influenzae-and some dental pathogenic streptococci make extracellular proteases that specifically inactivate antibodies of the secretory IgA class. They cleave IgA molecules at the hinge region to yield complete but relatively ineffective fragments. The proteases are present in active form in tissues and fluids infected by the bacteria that produce them. The absence of proteases in nonpathogenic bacteria suggests, although it does not prove, a role for IgA proteases in pathogenesis. For example, staphylococci produce staphylokinase, which cleaves host plasminogen into plasmin at the bacterial cell surface. This serine protease then degrades both immunoglobulin G and the complement protein C3b (see Table 8-2), which enables the microbe to avoid opsonization and phagocytosis. In some instances, it is known that when an organism cleaves IgA, the antigen-binding fragment (Fab) remains attached. The attached Fab fragment makes the antigens unavailable for binding by intact antibody molecules. This phenomenon has been called fabulation (after "Fab") and may serve to protect organisms from antibodies. Although these modes of transmission may seem passive, many infectious agents contribute actively to their transmission to new hosts. They do this by taking on traits specific for transmission or by producing molecules that cause the host to participate in transmissions. Many microbes differentiate into a transit form, a stage in their life cycle that helps them survive in the environment and in reservoirs or, if vectorborne, in insects. Among the animal parasites, transit forms usually differ greatly in structure and function from those that cause disease in the host, as in the case of worms or the protozoa that cause malaria. Note that living reservoirs and vectors shield infectious agents from deleterious environmental factors and obviate the need for the transit form to be highly resistant. In certain bacteria, such as the chlamydiae, the transit form (in this case called the elementary body) becomes encased in a tough envelope composed of highly cross-linked proteins (see Chapter 27). The chlamydia elemental body is thus reminiscent of the bacterial spore, the environmentally "tough" life form par excellence. In other bacteria, changes are more subtle and are revealed at the level of selective expression of certain genes, such as those involved in entering the stationary phase of growth. An active area of investigation is how infectious agents know where they are-that is, how they express different sets of genes outside and inside the body. The problems of transit are minimized when contact between hosts is direct and the agent is not subjected to prolonged exposure to the environment. In this context, it is logical that many sexually transmitted agents do not appear to have developed tough transit forms. Microbes can actively potentiate their spread from one host to another, thus providing themselves with new feeding grounds. To limit access from circulating defenses, herpes viruses do not usually enter the extracellular fluid but pass from cell to cell over cytoplasmic bridges. Intracellular herpesviruses reside within certain cells but do not proliferate; therefore, such a virus can avoid a host response and remain in a state called latency (see Chapters 41 and 42). A latent virus is not affected by antibodies, cell-mediated immunity, or interferon and can survive for a long time in an immunocompetent host without symptoms emerging. Latency is not restricted to viruses, as the tubercle bacillus Mycobacterium tuberculosis (see Chapter 23) can 126 Part 1: Principles contents in the environment. Some of the mechanisms developed by microbes for actively enhancing their transmission seem fiendishly clever. For example, the agent of plague, Yersinia pestis, is transmitted from an infected human to another by a flea bite. These bacteria greatly increase the efficiency of this transmission by making the flea feel hungry. The plague bacilli reproduce within the digestive tract of infected fleas, eventually causing blockage. To ward off starvation, the "blocked fleas" feed repeatedly and, during each feeding, regurgitate some of the contaminated material, thus increasing the chances of infecting a new host. The measures taken by each can be general or very specific; for every constitutive immune mechanism that hosts have to protect themselves, there is a microbe out there with the capacity to avoid it. Likewise, although the development of specific immunity is generally very effective for protecting against second infection, some microbes have developed impressive ways to steer clear of that response. The exquisite specificity of these responses points to coevolution of hosts and microbes. Given that microbes can go through multiple generations in a very short time and that they are constantly subject to new selection pressures, it is not surprising to find remarkable variation among pathogenic species. Evasive maneuvers by secreted bacterial proteins to avoid innate immune responses. Common strategies for antigenic variation by bacterial, fungal and protozoan pathogens. The story of microbial diseases is one of progressively escalating rounds of response and counterresponse from each side, Chapter 9 Joseph T. Advances in our understanding of the action of microbial toxins, coupled with our progress in understanding the molecular biology of the human cell, provide a framework to understand the molecular basis for microbial pathogenesis and the host response to infection. Damage during the infectious processes may be caused by the direct action of the microbial pathogen or by the host response to infection. These actions are often interrelated, and both are usually active during an infection. This chapter presents an overview of the cellular damage that occurs during infection and provides detailed descriptions of the major classes of microbial toxins. The pathology associated with cell death depends on the type and number of cells involved and the speed of the infectious process. If the infected cells are a component of an essential organ, such as the heart or the brain, the outcome is likely to be serious and could be fatal. For example, myocarditis, an infection of the heart muscle, is a fulminating and deadly disease when caused by the coxsackievirus. This virus is also thought to kill the insulin-producing cells of the islets of the pancreas and may be one cause of infantile diabetes. During a microbial infection, two mechanisms lead to cell death: cell lysis and programmed cell death. Lysis of host cells occurs in three ways: · the microorganism produces a toxin that affects the integrity of the cell membranes. In patients with gas gangrene, membrane-damaging toxins produced by one of the anaerobic clostridia lyse red blood cells. This is seen in Rocky Mountain spotted fever, which derives its name from the skin rash produced when endothelial cells of small vessels are killed by the intracellular growth of rickettsiae with the release of peroxide that damages membranes. This is observed when microorganisms that do not cause cell lysis directly, such as many viruses or mycobacteria, grow intracellularly. This process is a normal part of the mammalian cell cycle that ensures the maintenance of healthy cells. Some microorganisms, such as Shigella (the agent of dysentery), usurp this process when invading the host cell. In contrast, viruses, like the Epstein-Barr virus, block apoptosis and thereby immortalize the host cell. Pathological Alterations of Metabolism Certain infections do not kill cells directly but result in some of the most severe diseases, such as tetanus, botulism, cholera, and whooping cough. The pathology of each of these diseases is the result of a bacteriumproduced toxin that alters a key aspect of metabolism in ways that resemble the action of hormones or other pharmacological effectors. Although rare, such mechanical obstructions do occur in children with an overload of worms in their intestines. A heavy infestation with the large roundworm Ascaris (15 to 35 cm long and about 0. A single worm may also migrate into the common bile duct and obstruct the passage of bile. Often, mechanical obstruction results not from the microorganism but from the inflammatory response of the host. In elephantiasis, an enormous swelling of limbs or the scrotum is caused when small worms, called filariae, become lodged in lymphatics. The worms stimulate a tissue reaction that occludes the vessels, causing swelling and tissue hypertrophy. Almost any duct or tubelike organ, thick or thin, can be obstructed during an infection, sometimes with life-threatening consequences. Inflammation of the epiglottis may impede the passage of air; infection of the meninges can cause hydrocephalus (a dilatation of the cerebral ventricles resulting from obstruction of the flow of cerebrospinal fluid); infection of the prostate can obstruct the flow of urine from the bladder; and an inflammatory reaction to the eggs of the liver fluke may result in severe disturbances of the portal circulation. Although the overexpression of the host response contributes greatly to the immediate signs and symptoms of disease, it also helps the host survive. This is illustrated by tuberculosis, a chronic disease that some patients live with for many years. The term has become defined more broadly now to describe a range of proteins that alter the normal metabolism of host cells with deleterious effects on the host. Knowledge of how toxins work fosters an understanding of the pathophysiology of many infectious diseases and, in some instances, reveals important information about normal cellular processes of the host. The role of many toxins in causing disease has been studied in detail and will be described in chapters on specific bacterial pathogens. Here, the discussion focuses on the basic concept of how bacterial toxins damage the host. Although many toxins have been associated with bacterial diseases, toxins have not been implicated as important components of diseases caused by fungi, protozoa, or worms. The host response is rarely so finely tuned that only the infection is controlled. In gonorrhea, the gonococci set off the host response, an inflammation that accompanies copious pus production (pus comprises the products of dead immune cells) and swelling and accounts for disease symptoms. Likewise, in many chronic infections, like tuberculosis, damage to tissues is caused by chronic inflammation. The host response to infection is often owing to both inflammation and the immune response. Both operate in acute and chronic diseases and can manifest either locally or systemically. The mechanisms involved in inflammation are discussed in detail in Chapter 6, and those involved in immunopathology are discussed in Chapter 7. The role of inflammation and the immune response on cell damage will be further emphasized in chapters on individual diseases, where they may occupy center stage. Examples of host responses to infection leading to harmful outcomes for the host include (1) the accentuated inflammatory response that places patients with a brain abscess at risk of dying, (2) the overwhelming activation of the complement system that kills patients suffering from septicemia, (3) an autoimmune response that causes rheumatic fever, and (4) cell-mediated immunity responsible for manifestations of chronic tuberculosis. In Toxins that Modulate Intracellular Targets Toxins that modulate intracellular targets modify host targets through covalent mechanisms. Exotoxins are organized into three distinct domains that can bind surface receptors and stimulate the translocation of a catalytic domain into the cytosol of the host cell. Occasionally, exotoxins are bound to the surface or synthesized in the cytoplasm of the bacterium and released on lysis of the cell. In contrast, many pathogenic bacteria, such as staphylococci, streptococci, pseudomonads, and bordetellae, make several toxins. In such multifactorial situations, the importance of any one toxin is difficult to assess. Toxins share with antibiotics an ambivalent position in the life of the pathogen that produces them. On the one hand, toxins are dispensable because they are not required for bacterial growth. On the other hand, toxins may be essential for the survival and spread of the bacteria within the host. Upon maturation, the endosome acidifies, stimulating a conformational change in the B domain, which inserts into the endosome membranes to generate a pore that translocates the A domain into the cytosol. Bacterial exotoxins vary in their specificity; some act only on specific cells, while others affect a wide range of cells and tissues. Some bacteria make a single toxin, while other bacteria produce numerous toxins (Table 9-1). Some bacteria, like the pneumococci, make no known toxins and probably cause disease by toxin-independent mechanisms. Some toxins are produced continuously by growing bacteria; others are synthesized when the bacteria enter the stationary phase. The latter is often also true for antibiotics and other "secondary metabolites," which are produced as growth stops or slows down. In some instances, producing toxin only when the growth rate slows makes sense, because the toxin may help the bacterium obtain nutrients that have become scarce. Thus, high levels of diphtheria toxin are produced only when the diphtheria bacilli are iron starved. Because little free iron exists in normal tissues, it is believed that pathogenic bacteria obtain iron from cells killed by the toxin. In this process the bacterial cells in which the spores are formed eventually lyse, leading to the liberation of cytoplasmic proteins-including accumulated toxins.

Certain antigens zinc cholesterol levels 20 mg crestor with mastercard, such as capsular polysaccharides cholesterol free definition crestor 5 mg purchase visa, can be detected by a simple agglutination assay cholesterol blood test vap discount crestor online. Several widely performed tests use antibodycoated latex beads (latex agglutination tests) to detect capsular material from C cholesterol medication livalo order crestor 5 mg without a prescription. For many antigens cholesterol test price in india discount 20 mg crestor mastercard, the presence of the "captured" molecule is detected using a second antibody. The sample is incubated with an antibody-coated solid support, and the unbound material in the sample is washed away. An enzyme-labeled second antibody, which is also directed against the microbial antigen, is then added, forming a "sandwich" of the antigen between two layers of antibody. Similarly, the microbial culprit associated with an infection can often be identified by recognizing its products or parts, provided those parts are as specific for the pathogen as fingerprints are for a criminal. Identifications may be made either by detecting an antigen or a nucleic acid sequence that is specific for a pathogen. As you know from recent, celebrated criminal cases, prosecutors also use laboratory methods when traces of blood or body fluids are the available clues. Macromolecular detection tests have inherent disadvantages and advantages compared with standard culture diagnoses. If a multivalent antigen is present in the patient sample, bridges form between the particles, causing clumping. When there is much more antigen than antibody in the mixture, a false negative, or prozone phenomenon, may occur because no bridges between beads can form. Paradoxically, a serum sample that is negative because of a prozone reaction becomes positive when it is diluted. These basic formats have been adapted to simple kits to test for several pathogens in office practice. On the microscopic level, in situ hybridization may be performed on tissue sections. The precision of this interaction accounts for the high degree of specificity of nucleic acid­based tests. The mixture of labeled probe and sample is incubated, and the amount of probe hybridized to nucleic acids is measured. Consequently, each new strand becomes a new template for subsequent rounds of primer-initiated synthesis. Enzyme-conjugated specific antibody added; binds to E antigen, forming a "sandwich. Reduced isotope binding to the solid support indicates antigen present in the sample. In the "sandwich" assay format of the test, "capture" antibody bound to a solid support binds antigen from the patient sample. The presence of the captured antigen is detected using a second, specific antibody conjugated to an enzyme. Lastly, the activity of the enzyme bound to the solid support is measured using a color-producing substrate; color production signals the presence of the antigen, which is sandwiched between the two antibodies. In the competitive assay format, the patient sample is coincubated with a measured, small amount of purified, enzyme-labeled antigen over the same captured antibody solid support. If the patient sample contains no antigen, all the labeled antigens will complex with the antibody, and all the added enzyme-labeled antigen will be bound in immune complexes. If the patient sample contains antigen, it will compete with the labeled antigen for binding to the available antibody, and there will be minimal enzyme associated with immune complexes. Commercial nucleic acid amplification assays now in common use include tests to detect the presence of M. Note that synthesis from either primer generates a new site to which the opposite primer can hybridize in the next cycle. The products of the reaction are detected by gel electrophoresis or by a gene probe specific for the sequences between the two primers. One popular version of the technique employs a fluorescent-labeled probe that hybridizes to the newly synthesized amplicons. The typical result of this method and others is that the intensity of the fluorescence in the reaction vessel increases as more amplicons are generated. Second, it offers the possibility of quantifying the target nucleic acid sequence in the original sample by measuring the number of cycles required to reach a threshold of fluorescence detection. Theoretically, the chain reaction can be initiated by a single copy of the target sequence. A serious potential for cross-contamination (microcontamination) exists in laboratories that process many similar samples every day. Simpson, in which questions about mishandling of specimens and crosscontamination of evidence may have influenced the verdict. To avoid cross-contamination in clinical diagnostic laboratories, specimen preparation and amplification are performed in separate areas. Microarrays A disadvantage of nucleic acid­based tests and antigen detection assays is that they can tell the physician only whether a particular pathogen is present in a sample. As a diagnostic tool, bacterial culture has an advantage over those methods because it does not require the physician to guess which pathogens may be present and to test for each individually. One culture can detect an enormous variety of pathogenic organisms by a single method. Advances in microchip technology have created the possibility of using nonculture diagnostics in a similar manner. A microchip can be printed to contain hundreds of oligonucleotide probes bound in an array no bigger than a microscopic slide. Conjugated to this detection probe are a fluorescent dye and a fluorescence quencher in close proximity to one another, such that the fluorescence from the dye is quenched and is undetectable. As they separate from one another, the fluorescent dye becomes active and emits a signal. By reference to these standards, the number of target nucleic acid molecules in a patient sample can be determined. The products of such a reaction could then be hybridized with a microarray containing the known intervening sequences from hundreds of bacterial species. It would then be possible to determine which one (or ones) is (are) present in the patient sample. During the amplification process, the amplicons are labeled with a fluorescent dye­conjugated primer. Finally, the amplicons are hybridized to a microarray that has bound oligonucleotides representing the inventing sequences from hundreds of bacterial species. In this case, the amplicons bind to the sequences characteristic of Escherichia coli, identifying E. All methods have the potential for inaccuracy, either in failing to detect a pathogen or immune response when present or in signaling their presence when the pathogen or the immune response is absent. Some tests are more sensitive or more specific than others, and those measures of performance determine how and when they are used. However, even when a test accurately analyzes a given sample, the simple presence of a microorganism in the specimen or of antibodies against a pathogen in patient serum does not always indicate active infection, nor does it necessarily establish the cause of illness. Therefore, interpretation is always necessary with any microbiologic test, regardless of its technical performance characteristics. Developing molecular amplification methods for rapid diagnosis of respiratory tract infections caused by bacterial pathogens. When infectious agents are involved, the aim is to understand their mode of transmission and what predisposes a population to a particular agent. The practical purpose of epidemiology is to control the spread of disease in a population, either by limiting microbial transmission or by altering the susceptibility of a population through public health interventions. Common control measures include removing the source of the agent, active surveillance of suspected cases, control of transmission through quarantine or personal protective measures, and protection of the population through immunization or prophylactic treatment with antibiotics. This chapter considers epidemiological concepts and methods through the examination of an epidemiological "case," the investigation of a new disease. Following the case discussion, the chapter considers general epidemiological issues. However, before considering a case, the reader should review some of the key terms that are commonly used in the field of epidemiology (Table 59-1). It is one of the most useful methods of infectious disease epidemiology, but it is by no means the only one. Others, including case­control studies, cohort studies, and epidemiological interventions, used in investigating both infectious and noninfectious diseases are discussed later in this chapter. An epidemic investigation is typically undertaken when the number of cases of a disease increases over what is considered to be the norm or standard. In the Connecticut study, it was necessary to determine first if the arthritis cases did indeed represent an epidemic. In October 1975, the Department of Health of Connecticut received separate calls from two mothers living on rural roads in the towns of Lyme and Old Lyme. They reported that several children in their households and their neighborhoods had what appeared to be arthritis. They had voiced their concern to local physicians and were not deterred by being told that arthritis is "not infectious. What steps should epidemiologists take, and what principles should they apply to studying the reported cases, after discussions with the parents and local physicians Characteristics such as previous exposures are then compared between cases and controls. A type of observational analytic study in which a well-defined group of people with common exposures are followed through time. Disease, death, or other health-related outcomes are then ascertained and compared. The occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time A histogram that shows the course of a disease outbreak or epidemic by plotting the number of cases by time of onset. The frequency of new cases of illness in a population over a period of time A period of subclinical or inapparent pathologic changes following exposure, ending with the onset of symptoms of infectious disease An epidemic occurring over a very wide area (several countries or continents) and usually affecting a large proportion of the population the amount of a particular disease present in a population at a single point in time A personal behavior, lifestyle, exposure, or inherited characteristic that is associated with an increased occurrence of disease or other health-related event or condition An animate intermediary in the indirect transmission of an agent that carries the agent from a reservoir to a susceptible host An infectious disease that is transmissible under normal conditions from animals to humans Example Some pathogens transmitted by the respiratory route such as measles and varicella have a very high attack rate among vulnerable hosts. Clinical trials that are not blinded and do not use placebo controls may be biased because researchers and patients may expect to get better with a certain treatment. Rabies has one of the highest case-fatality rates of any infection, since only a few individuals have ever survived. Outbreak investigations are a form of case­control study since usually characteristics of disease cases are compared with healthy controls to figure out which exposure contributed to the outbreak. Toxin-mediated food poisoning has a much shorter incubation period than invasive disease because often the toxin is preformed in the food that is consumed. In 2009, the World Health Organization declared an H1N1 influenza pandemic, in which nearly every country identified cases. Bias Case-fatality rate Case-control Cohort Epidemic Epidemic curve Incidence Incubation period Pandemic Prevalence Risk factor Vector the Anopheles mosquito is the vector for malaria transmission. Brucellosis is a zoonosis that can be transmitted through unpasteurized goat or sheep milk. For example, before the advent of the polio vaccine in the 1950s, about 50,000 cases of the disease occurred in the United States annually. After the vaccine was put into widespread use, the number of cases dropped dramatically to about 10 per year. Therefore, one or two cases of polio after widespread vaccination might be considered an epidemic. Number of Cases 1 5 1974 1 5 Case Definition the investigators of the cases of arthritis in Connecticut began by asking whether other individuals had the same disease. They first had to establish a set of clinical criteria known as the case definition. From the mothers, physicians, and school nurses in the area, they obtained a list of other individuals who may have had the same symptoms. After examining those people and taking careful histories, the epidemiologists included, as fitting the case definition, individuals with the following clinical picture: a sudden onset of swelling and pain in a knee or other large joint lasting a week to several months, several attacks that recurred several times at intervals over a few months, and/or fever and fatigue. Clustering of cases of Lyme disease in three towns in Connecticut (Lyme, Old Lyme, and East Haddam) between 1972 and 1975. Time, Place, and Personal Characteristics of Patients Armed with a usable case definition, the investigators found other cases in Old Lyme and two adjacent towns. The best sources of additional cases were the two determined mothers who had made the original phone calls. From current and past episodes, the investigators collected 51 cases that conformed to the case definition. They could now try to identify the risk factors for the clinical syndrome by carefully determining what epidemiologists call the time, place, and personal characteristics of the cases. The time characteristics include the time of onset of the disease and its duration. Age, sex, nutritional status, previous exposure, and immune competence all influence susceptibility to a particular infectious disease. For instance, children and older persons frequently are more likely to contract bacterial pneumonia or intestinal infections. The incidence of the carrier state of hepatitis B is greater in males than in females. It is also more frequent among individuals with Down syndrome or those receiving hemodialysis. Genetic factors are also known to play a role in susceptibility, although the mechanisms by which specific genes contribute are just now being determined. Why do some colonized patients develop overwhelming meningococcal disease, for instance, and others do not The importance of genetic factors is often difficult to differentiate from a myriad of socioeconomic factors that might contribute to the state of health and nutrition. Nonetheless, the role of genetic factors has been well established in certain diseases. However, in reality it pervades all forms of medical practice and furnishes particularly important clues to the diagnosis of infectious diseases. Inquiry into time and place characteristics is not only the foundation of outbreak investigation but should be part of the usual process of taking a clinical history.

Although you need to know only the principal bacteria total cholesterol chart uk buy crestor 10 mg, even they make up a long list cholesterol granuloma definition buy crestor without prescription. However cholesterol test price in india buy 5 mg crestor overnight delivery, knowing the taxonomy of bacteria may help you make important diagnostic and treatment decisions cholesterol chinese food order crestor cheap. For example cholesterol ratio 5 order crestor with mastercard, among other things, it is helpful to know that staphylococci and streptococci both belong to a group called the Gram-positive cocci, that Escherichia coli is classified among the Gram-negative enteric bacteria, and that the tubercle bacillus belongs to the acid-fast bacteria. This chapter uses a simplified, practical scheme to divide the main pathogenic bacteria, rather than the organizational scheme used in the science of bacterial taxonomy. In broad terms, medically interesting bacteria belong to one of two large categories: 1. The "typical" bacteria-the rods and cocci (spheres) that lack unusual morphological features. These "garden variety" bacteria can be subdivided into the Gram-positive and Gram-negative bacteria, and each of those categories can be further divided into rods and cocci. Like all other forms of life, each bacterium is named by its genus, as in Escherichia, and species, as in coli. Conventionally, after its first use in a text, the genus name is shortened to the first letter, as in E. Many bacteria also have common names, usually related to the main disease they cause-for example, the meningococcus (Neisseria meningitidis) and the tubercle bacillus (Mycobacterium tuberculosis). Sometimes the origin of the genus and species names is interesting and useful to know. Many bacterial names honor famous microbiologists; for instance, Escherichia is named after the German pediatrician Theodor Escherich and Salmonella after the American veterinarian Daniel Elmer Salmon. Other names are descriptive; pyogenes (as in Streptococcus pyogenes), for example, indicates that the bacteria promote pus production. A confusing aspect of bacterial taxonomy is that considerable variety usually exists within a species. Thus, a Staphylococcus aureus isolated from one patient may be distinctly virulent, whereas another strain of the same bacterium may not be. The chief differences that the Gram stain illustrates are presence of an outer membrane in the Gram-negative bacteria and of a thick murein layer in the Gram-positive bacteria (see Chapter 3). These organisms can also be divided into rods and cocci, yielding four categories in which to classify them. This illustration is a practical representation of the principal groups of pathogenic bacteria. Many of the chapters on individual infectious agents include sections called paradigms. These sections highlight points of general relevance to the understanding of microbial pathogenesis. Because the Gram stain reflects such fundamental differences among bacteria, Gram-positive bacteria differ more from Gram-negative bacteria than cocci differ from rods. For instance, the Gram-positive streptococci are closely related to the lactobacilli, which are Gram-positive rods; however, the streptococci are quite distinct from Gram-negative cocci, such as the gonococci. Gram-positive bacteria accept the Gram stain and appear dark violet, whereas Gram-negative bacteria do not accept the stain and appear red (see Chapter 3 and Table 3-2). The Gram-positive cocci and the Gramnegative rods are the most common agents of infection, followed by the Gram-negative cocci and the Gram-positive rods. Species within each genus are among the most successful human pathogens and, consequently, are the targets of vigorous research efforts to understand and combat them. Streptococci Streptococci grow in chains of spherical cells-like strings of pearls-and constitute a large and diverse group. Streptococci are subdivided according to the changes they produce when grown on agar-containing blood. Thus, b-hemolytic streptococci (or "beta strep"), which cause most streptococcal infections, lyse red blood cells signified by a clear area around the colonies. The a-hemolytic streptococci produce a different change and cause blood-containing media around the colony to turn green. Many streptococci strains are nonpathogenic and are found in the environment as well as in the normal human intestine. Fermentation is characteristic of anaerobic bacteria, and indeed some streptococci are strict anaerobes. However, most of the pathogenic species of streptococci grow in air and are thus described as oxygen-tolerant anaerobes. Streptococci produce many extracellular proteins, some of which are virulence factors that confer on the organisms the ability to destroy tissues and damage host cells. These strains are further subclassified into groups by the presence of different cell wall polysaccharides. Of all the groups (A through T), the most important strains in human disease are those of group A. These infections can cause serious complications, such as rheumatic fever or glomerulonephritis. They are the most likely organisms to cause pus in wounds and may produce serious infections in deep tissues, such as osteomyelitis (infection of the bone marrow) or endocarditis (infection of the heart valves). Like the streptococci, they secrete a large number of extracellular enzymes and toxins. One enzyme, coagulase, clots plasma and is useful in distinguishing the most pathogenic species of the genus, S. Gram-Negative Cocci Gram-negative cocci include several genera of medical importance, the most significant of which is Neisseria. This genus includes many organisms found in the mouth and pharynx of healthy people and two important pathogens, gonococcus (N. Like all Gram-negative bacteria, their outer membranes contain endotoxin (lipopolysaccharide). The gonococcus causes gonorrhea, and the meningococcus causes meningitis and severe septicemia. Gram-Positive Rods Abundant in the environment, this group includes bacteria that only infrequently cause diseases, at least in the developed regions of the world. One disease, diphtheria, was deadly among children until vaccination nearly eradicated it. The agent of diphtheria is called Corynebacterium diphtheriae and has many relatives called the diphtheroids. The diphtheroids are common inhabitants of the skin and mucous membranes and can cause opportunistic infections. They are the largest of the typical bacteria, with 5 to 10 times the volume of an average E. They are divided into two genera: the aerobic Bacillus, containing only one important pathogenic species, B. Among the most commonly encountered clostridial disease is one associated with antibiotic use: pseudomembranous colitis caused by C. Another important pathogen among the Grampositive rods is Listeria monocytogenes, which occasionally causes serious infections in infants and in adults who are immunocompromised and in pregnant women. Under the microscope, staphylococci look like arrays of buckshot or bunches of grapes (staphylo comes from the Greek word for grapes). They are more robust than streptococci and are able to withstand many chemical and physical agents; these qualities make it difficult to eradicate them from the human environment. Gram-Negative Rods Enteric Bacteria the Gram-negative rods are a large group of bacteria that includes many important pathogens. The enteric 146 Part 2: Infectious Agents bacteria are among the most clinically important of the Gram-negative rods. The enteric bacteria (or family Enterobacteriaceae) comprise many genera, including Salmonella, species of which cause typhoid fever and food poisoning, and Shigella, which causes bacillary dysentery. All enteric bacteria grow readily on laboratory media, make colonies typically less than 1 mm across on agar, and do not form spores or have distinct cell arrangements. Although many pathogens are not lactose fermenters, the characteristic is not universal, and many exceptions exist. Relatives of the enteric bacteria include the yersiniae, which cause plague and certain intestinal infections. Among their more distant relatives are Gram-negative rods that differ in metabolism and somewhat in morphology. These are in various families outside the Enterobacteriaceae, including the genus Vibrio (containing V. Pseudomonads, as the members of the Pseudomonas genus are sometimes called, are often found in aqueous environments, such as rivers, lakes, swimming pools, and tap water; these environments are thus frequent sources of human infection. Other clinically important Gram-negative rods outside the Enterobacteriaceae are Campylobacter jejuni, a common agent of infectious diarrhea, and Helicobacter pylori, which causes gastritis, gastric ulcers, and gastric cancer. These organisms usually do not cause disease alone but are found in association with other bacteria, thereby causing mixed or polymicrobial infections. They will not reproduce if incubated aerobically, and their growth requires special anaerobic techniques. Acid-Fast Bacteria this group is almost synonymous with the genus Mycobacterium, which includes the tubercle bacillus, M. The name "Mycobacterium" contains the root word for fungus (myco) because the organisms sometimes form branches that vaguely suggest the fungi. There acid fastness refers to the ability of these organisms to resist decolorization by acids, a trait that is exploited in specialized staining procedures (see Chapter 3). The Gram stain is not useful for identifying these bacteria because they do not take up the Gram stain dyes. They are surrounded by a waxy envelope that can only be penetrated by dyes if the bacteria are heated or treated with detergents. All mycobacteria grow slowly (perhaps taking days or even weeks to form a colony on agar media) and are resistant to chemical agents but not to heat. The special staining procedure used for acid-fast bacteria is called the Ziehl-Neelsen technique. Its most frequently used modification consists of treating smears with a solution of a red dye (fuchsin) that contains detergents. After washing, the smear is treated with a solution of 3% hydrochloric acid that removes the dye from all bacteria except the acid-fast organisms. The preparation is then exposed to a blue dye that counterstains all other bacteria, white blood cells, and so on. Tubercle or leprosy bacilli, which stain red in this procedure, are clearly visible against the blue background. Several species of mycobacteria found free living in the environment can cause opportunistic infections, especially in immunocompromised patients. Among the most commonly encountered of these bacteria are members of a complex known as Mycobacterium avium-intracellulare. Even more akin to fungi in morphology are relatives of the mycobacteria called the actinomycetes. These "Fastidious" and Small Gram-Negative Rods Besides the organisms already mentioned, the Gramnegative rods include an important and heterogeneous group of genera. They can be lumped, somewhat arbitrarily, into a group that may be awkwardly described as the "fastidious" and small Gram-negative rods because they have complex nutritional requirements and tend to be smaller than, for example, E. Included in this group are the following genera: Haemophilus (which causes pneumonia and meningitis), Bordetella (whooping cough), Brucella (brucellosis), Francisella (tularemia), Bartonella (cat scratch fever), and Legionella (Legionnaires disease, a form of pneumonia). Strictly Anaerobic Gram-Negative Rods An important group of Gram-negative rods is distinguished by its strictly anaerobic way of life. Clinically, the most noteworthy of these organisms belongs to the genus Bacteroides. These bacteria are common in the human body and are the most frequent members of the intestinal microbiota, where they may serve as a critical stimulus for proper tissue development within the intestine and break down some polysaccharides in the human diet. Although the bacteria are usually Chapter 10: Introduction to the Pathogenic Bacteria 147 organisms take up the Gram stain and are Gram-positive, although some are also weakly acid-fast. They form true branches and long filaments with complex structures, a feature that places them among the most highly differentiated of the prokaryotes. There are two pathogenic genera: Nocardia, which are aerobic, and Actinomyces, which are strict anaerobes. Bacteria of these genera cause certain forms of pneumonia and soft tissue infections. A generally nonpathogenic genus, Streptomyces, includes organisms that make important antibiotics (streptomycin, tetracycline, etc. They are almost plastic in structure, grow slowly on laboratory media, and have special nutritional requirements. The most unique of these is the need for sterols, which are not required by any other group of bacteria. Mycoplasmas lack murein and consequently are resistant to penicillin and other cell wall antibiotics. The oldest known human pathogenic mycoplasma is Mycoplasma pneumoniae, which causes a form of pneumonia. Mycoplasmas resemble the laboratory-produced forms of regular bacteria-the so-called L forms- which lack cell walls. Regular bacteria take on the same amorphous appearance as the mycoplasma when their cell walls are removed with lysozyme or when murein synthesis is inhibited with penicillin. Cell lysis usually occurs, but if the L forms are placed in a hypertonic medium, they can be grown in colonies that resemble those of the mycoplasmas. L forms usually revert to the regular bacterial form when they are removed from lysozyme or penicillin. Further, they are thought to have the smallest genomes among free-living organisms. Because of this, they have been the subject of a significant amount of research regarding the evolution of genome structure and function. In 2010 a group of scientists claimed the creation of the first "synthetic" microbe by replacing the natural chromosome of a mycoplasma cell with a laboratory-synthesized chromosome. Spirochetes these bacteria are helical, having the shape of a spring (not a screw).

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