Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Epidemiology, tracking diseases with technology

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Analysis of a proper sample size, as well as study type

are techniques belonging to epidemiology and statistics. They

were developed in order to produce reliable information from

a study regarding the association of genetic and environmen-

tal factors. Studies that are more descriptive consider genetic

trait frequency, geographic distribution differences, and preva-

lence of certain conditions in different populations. On the

other hand, studies that analyze numerical data consider fac-

tors like association, probability of occurrence, inheritance,

and identification of specific groups of individuals.

Thus, molecular epidemiology arises from varied scien-

tific disciplines, including genetics, epidemiology, and statis-

tics. The strategies involved in genetic epidemiology en-

compass population studies and family studies. Sophisticated

mathematical tools are now involved, and computer technology

is playing a predominant role in the development of the disci-

pline. Multidisciplinary collaboration is crucial to understand-

ing the role of genetic and environmental factors in disease

processes.

See alsoBacteria and bacterial infection; Genetic identifica-

tion of microorganisms; History of microbiology; History of

public health; Infection control; Public health, current issues;

Transmission of pathogens

EPIDEMIOLOGY, TRACKING DISEASES

WITH TECHNOLOGYEpidemiology, tracking diseases with technology

Epidemiologyis a term that refers to the techniques and analy-

sis methods that are used to pinpoint the source of an illness.

As well, epidemiologists (those who conduct the epidemio-

logical 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 diseasecaused 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 possi-

ble causes of the infection. This saves time, since the elimina-

tion 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 hepatitisvirus.

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 coliO157: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 anti-

bodies 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 PCRtend 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 resist-

ancebacteria 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 infec-

tion. Knowing what antibioticswill 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 out-

break 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 AIDSin North America provides an exam-

ple 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 atten-

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