epidemiology.bmpLoosely defined, epidemiology is the study of diseases and conditions as they move through populations of people, one objective being to identify the source of injury so that the cause can be eliminated.  Ross Anderson’s article today in Food Safety News, spawned by the hazelnut E. coli outbreak, is a good primer on the science:

Seven sick people, most of them middle-aged men, scattered across three states. As epidemiology goes, that’s not much to go on.

To track outbreaks of foodborne illness, the “epi” sleuths usually need numerous sick people, preferably concentrated in one or two areas. Larger “clusters” of illnesses greatly improve the chance of figuring out what made everybody sick.

But you go with what you got, says Josh Rounds, a staff epidemiologist at the Minnesota Department of Health in St. Paul. And just three weeks ago, in mid-February, what the MDH had was three cases of E. coli O157:H7 in Minnesota, three more in neighboring Wisconsin, and one in Michigan. Three of the case patients had been hospitalized.

None of the sick knew each other, nor had they eaten at the same restaurant or church potluck. They live hundreds of miles apart. Yet lab tests showed they had contracted the same strain of E. coli, so they were all contaminated by a single source. Minnesota launched its investigation, and Rounds got the job.

Step One: “Team D,” short for Diarrhea, students in public health studies at nearby University of Minnesota, who work part time for the state health department. Most work in the evenings, working the phones, interviewing people who have been ill. Each interview follows the same format – a 12 page questionnaire, inquiring what victims ate before they got sick.

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