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Disease and Resistance: The War Within |
Chapter: 16
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By the Book Investigating an outbreak of disease can be difficult if one only has intuition to rely on. Fortunately, the investigators at the Centers for Disease Control and Prevention (CDC) have a prescribed protocol to help them nail down the source of an infectious disease.
Imagine that an illness has broken out in a group of people. First, a case must be defined according to the predominant symptoms seen in the patients. For a foodborne illness, these might include diarrhea, with at least three stools per day; nausea; cramps; and abdominal pain. Then the disease cluster is studied: What food was served? How was it prepared? Did the sick people eat something that well people did not eat?
Another approach is the case-control study. This method is used for isolated cases. Officials interview the sick individuals (the "cases") and several unaffected associates (the "controls") in an attempt to pinpoint a food they can tie to those who became ill. Finally, the agency conducts a trace-back study to identify the source of the food.
These methods have evolved over the many decades of the CDC’s existence. They provide the motive, method, and opportunity for an outbreak of disease. And they work—most of the time. |
