Chapter 1 Infection

We do not know everything and not all of what we

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and be prepared for new developments which clarify, or in some cases, alter them. We do not know everything, and not all of what we believe we know is correct. Epidemiology Epidemiology is the "who, what, when, and where" of infectious diseases. The power of the science of epidemiology was first demonstrated by Semmelweis, who by careful data analysis alone determined how streptococcal puerperal fever is transmitted. He even devised a means to prevent transmission (ie, handwashing) decades before the organism itself was discovered. Since then, each organism has built its own profile of vital statistics. Some agents are transmitted by air, others by food, and others by insects; some spread by the person-to-person route. Figure 1–5 presents some of the variables in this regard. Some agents occur worldwide, and others only in certain geographic locations or ecologic circumstances. Knowing how an organism gains access to its victim and spreads is crucial to understanding the disease. It is also essential in discovering the emergence of "new" diseases, whether they are truly new (AIDS) or just recently discovered (Legionnaires disease). Solving mysterious outbreaks or recognizing new epidemiologic patterns have usually pointed the way to the isolation of new agents.
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Epidemic spread and disease are facilitated by malnutrition, poor socioeconomic conditions, natural disasters, and hygienic inadequacy. In previous centuries, epidemics, sometimes caused by the introduction of new organisms of unusual virulence, often resulted in high morbidity and mortality rates. The possibility of recurrence of old pandemic infections remains, and, as with AIDS, we are currently witnessing a new and extended pandemic infection. Modern times and technology have introduced new wrinkles to epidemiologic spread. Intercontinental air travel has allowed diseases to leap continents even when they have very short incubation periods (cholera). The efficiency of the food industry has sometimes backfired when the distributed products are contaminated with infectious agents. The well- publicized outbreaks of hamburger-associated Escherichia coli O157:H7 infection constitute an example. The nature of massive meat-packing facilities allowed organisms from infected cattle on isolated farms to be mixed with other meat and distributed rapidly and widely. By the time outbreaks were recognized, cases of disease were widespread, and tons of meat had to be recalled. In simpler times, local outbreaks from the same source would have been detected and contained more quickly. Of course, the most ominous and uncertain epidemiologic threat of these times is not amplification of natural transmission but the specter of unnatural, deliberate spread. Anthrax is a disease uncommonly transmitted by direct contact of animals or animal products with humans. Under natural conditions, it produces a nasty but usually not life-threatening ulcer. The inhalation of human-produced aerosols of anthrax spores could produce a lethal pneumonia on a massive scale. Smallpox is the only disease officially eradicated from the world. It took place so long ago that most of the population has never been exposed or immunized and are thus vulnerable to its reintroduction. We do not know whether infectious
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We do not know everything and not all of what we believe we...

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