Epidemiology is the study of the various factors that influence the occurrence, distribution, prevention, and control of disease, injury, and other health-related events in a defined human population. By the application of various analytical techniques including mathematical analysis of the data, the probable cause of an infectious outbreak can be pinpointed. This connection between epidemiology and infection makes microorganisms an important facet of epidemiology, and gives epidemiologists a vital link in emergency planning for public health response to a biological attack.
Many illnesses of epidemiological concern are caused by microorganisms. Examples include hemorrhagic fevers such as that caused by the Ebola 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., contact, air borne, insect borne, food and water intake, etc.). Likewise, the route of entry of an infectious microbe can also vary from microbe to microbe.
If an outbreak is recognized early enough, samples of the suspected cause as well as samples from the afflicted (i.e., sputum, 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 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 tends to limit its use to more of a confirmatory role, rather than as an initial tool of an investigation. A considerable research effort is ongoing world over to develop quicker, less expensive and more portable PCR equipment that can be used by inspectors and investigators.
Another epidemiological tool is the determination of the antibiotic susceptibility and resistance of bacteria. 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. In addition to geographic based 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 and 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.
Reconstructing the movements of people is especially important when the outbreak is 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.
Epidemiologists were among the first scientists to effectively utilize the Internet and email capabilities to effectively communicate regarding disease outbreaks. The International Society for Infectious Diseases sponsors PROMED, the global email based electronic reporting system for outbreaks of emerging infectious diseases and toxins, is open to all sources.
(Author is pursuing Doctoral Program in Epidemiology and is working as Epidemiology consultant)
