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Experimental studies provide the strongest evidence for the etiology of disease, but they must also be designed carefully to eliminate subtle effects of bias . Typically, experimental studies with humans are conducted as double-blind studies , meaning neither the subjects nor the researchers know who is a treatment case and who is not. This design removes a well-known cause of bias in research called the placebo effect , in which knowledge of the treatment by either the subject or the researcher can influence the outcomes.
Since laboratory tests had confirmed Salmonella , a common foodborne pathogen, as the etiologic agent, epidemiologists suspected that the outbreak was caused by contamination at a food processing facility serving the region. Interviews with patients focused on food consumption during and after the Thanksgiving holiday, corresponding with the timing of the outbreak. During the interviews, patients were asked to list items consumed at holiday gatherings and describe how widely each item was consumed among family members and relatives. They were also asked about the sources of food items (e.g., brand, location of purchase, date of purchase). By asking such questions, health officials hoped to identify patterns that would lead back to the source of the outbreak.
Analysis of the interview responses eventually linked almost all of the cases to consumption of a holiday dish known as the turducken —a chicken stuffed inside a duck stuffed inside a turkey. Turducken is a dish not generally consumed year-round, which would explain the spike in cases just after the Thanksgiving holiday. Additional analysis revealed that the turduckens consumed by the affected patients were purchased already stuffed and ready to be cooked. Moreover, the pre-stuffed turduckens were all sold at the same regional grocery chain under two different brand names. Upon further investigation, officials traced both brands to a single processing plant that supplied stores throughout the Florida panhandle.
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Match each type of epidemiology study with its description.
| ___experimental | A. examination of past case histories and medical test results conducted on patients in an outbreak |
| ___analytical | B. examination of current case histories, interviews with patients and their contacts, interpretation of medical test results; frequently conducted while outbreak is still in progress |
| ___prospective | C. use of a set of test subjects (human or animal) and control subjects that are treated the same as the test subjects except for the specific treatment being studied |
| ___descriptive | D. observing groups of individuals to look for associations with disease |
| ___retrospective | E. a comparison of a cohort of individuals through the course of the study |
C, D, E, B, A
Match each pioneer of epidemiology with his or her contribution.
| ___Florence Nightingale | A. determined the source of a cholera outbreak in London |
| ___Robert Koch | B. showed that surgical wound infection rates could be dramatically reduced by using carbolic acid to disinfect surgical tools, bandages, and surgical sites |
| ___Joseph Lister | C. compiled data on causes of mortality in soldiers, leading to innovations in military medical care |
| ___John Snow | D. developed a methodology for conclusively determining the etiology of disease |
C, D, B, A
________occurs when an infected individual passes the infection on to other individuals, who pass it on to still others, increasing the penetration of the infection into the susceptible population.
Propagated spread
A batch of food contaminated with botulism exotoxin, consumed at a family reunion by most of the members of a family, would be an example of a ________ outbreak.
point source
What activity did John Snow conduct, other than mapping, that contemporary epidemiologists also use when trying to understand how to control a disease?
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