Epidemiology, Tracking Diseases with Technology (World of Microbiology and Immunology)
Epidemiology is a term that refers to the techniques and analysis methods that are used to pinpoint the source of an illness. As well, epidemiologists (those who conduct the epidemiological investigations) are concerned with the distribution of the infection.
Typically, epidemiology is concerned with an illness outbreak involving the sudden appearance of a disease or other malady among a group of people. Examples of situations where epidemiology would be of use are an outbreak of food poisoning among patrons of a restaurant, or a disease outbreak in a geographically confined area.
Many illnesses of epidemiological concern are caused by microorganisms. Examples include hemorrhagic fevers such as that caused by the Ebola virus, toxic shock syndrome, Lyme disease caused by the Norwalk virus, and Acquired Immunodeficiency Syndrome caused by the Human Immunodeficiency Virus. The determination of the nature of illness outbreaks due to these and other microorganisms involve microbiological and immunological techniques.
Various routes can spread infections (i.e., on contact, air borne, insect borne, food, water). Some microorganisms are spread via a certain route. For example, Coxiella burnetii, the cause of Q fever, is spread from animals to humans via the air. Knowledge of how an infection was spread can suggest possible causes of the infection. This saves time, since the elimination of the many infectious microorganisms requires a lot of laboratory analysis.
Likewise, the route of entry of an infectious microbe can also vary from microbe to microbe. Hepatitis viruses are transmitted via direct contact (e.g., sharing of needles). Thus, a water-borne illness is likely not due to a hepatitis virus.
If an outbreak is recognized early enough, samples of the suspected cause (i.e., food, in the case of a food poisoning incident) as well as samples from the afflicted (i.e., feces) can be gathered for analysis. The analysis will depend on the symptoms. For example, in the case of a food poisoning, symptoms such as the rapid development of cramping, nausea with vomiting, and diarrhea after eating a hamburger would be grounds to consider Escherichia coli O157:H7 as the culprit. Analyses would likely include the examination for other known microbes associated with food poisoning (i.e., Salmonella) in order to save time in identifying the organism.
Analysis can involve the use of conventional laboratory techniques (e.g., use of nonselective and selective growth media to detect bacteria). As well, more recent technological innovations can be employed. An example is the use of antibodies to a known microorganism that are complexed with a fluorescent particle. The binding of the antibody to the microbes can be detected by the examination of a sample using fluorescence microscopy or flow cytometry. Molecular techniques such as the polymerase chain reaction are employed to detect genetic material from a target organism. However, the expense of the techniques such as PCR tend to limit its use to more of a confirmatory role, rather than as an initial tool of an investigation.
Another epidemiological tool is the determination of the antibiotic susceptibility and resistance of bacteria. This is especially true in the hospital setting, where antibiotic resistance bacteria are a problem in nosocomial (hospital acquired) infections. An outbreak of illness in a hospital should result in a pre-determined series of steps designed to rapidly determine the cause of the infection, to isolate the infection to as small an area of the hospital as possible, and to eliminate the infection. Knowing what antibiotics will be effective is a vital part of this strategy.
Such laboratory techniques can be combined with other techniques to provide information related to the spread of an outbreak. For example, microbiological data can be combined with geographic information systems (GIS). GIS information has helped pinpoint the source of outbreaks of Lyme disease. As well, the outbreak patterns can be used in the future to identify areas that will be high-risk areas for another outbreak. Besides geographic information, epidemiologists will use information including the weather on the days preceding an outbreak, mass transit travel schedules and schedules of mass-participation events that occurred around the time of an outbreak to try an establish a pattern of movement or behavior to those who have been affected by the outbreak. Use of credit cards and bank debit cards can also help piece together the movements of those who subsequently became infected.
The spread of AIDS in North America provides an example of the result of an epidemiological study of an illness. Analysis of the pattern of outbreaks and tracing the behavioral patterns of those who became infected led to the conclusion that the likely originator of the epidemic was a flight attendant. Because of his work, he was well traveled. His sexual behavior helped spread the virus to sexual partners all over North America, and they subsequently passed the virus on to other partners. Without the techniques and investigative protocols of epidemiology, the source of the AIDS epidemic would not have been resolved.
Reconstructing the movements of people is especially important when the outbreak is of an infectious disease. The occurrence of the disease over time can yield information as to the source of an outbreak. For example, the appearance of a few cases at first with the number of cases increasing over time to a peak is indicative of a natural outbreak. The number of cases usually begins to subside as the population develops immunity to the infection (e.g., influenza). However, if a large number of cases occur in the same area at the same time, the source of the infection might not be natural. Examples include a food poisoning or a bioterrorist action.
The ultimate aim of the various steps taken in an epidemiological investigation is to prevent infections by the use of prudent public health measures, rather than having to rely on reactive steps such as vaccination to defeat ongoing infections. Indeed, for some infections (i.e., HIV, hepatitis B and C) vaccination may not ultimately prove to be as effective as the identification of the factors that promote the diseases, and addressing those factors.
See also Bacteria and bacterial infection; Epidemics and pandemics; Laboratory techniques in immunology; Laboratory techniques in microbiology