Use of the case-control method in outbreak investigations.

The authors carried out a critical assessment of the literature to learn about the extent of use of the case-control method in outbreak investigations, and to identify problems observed in the use of this method to investigate outbreaks. The literature search comprised reports of outbreak investigations from the MEDLINE system, Morbidity and Mortality Weekly Report, and six epidemiologic and medical journals. The proportion of these reports that used the case-control method increased from one article out of 519 in the 1960-1965 period to 144 out of 845 reported outbreaks in the 1980-1985 period. A comparison of the case-control studies of outbreak investigations in the 1970-1975 period with those in the 1980-1985 period revealed relatively more sophisticated methods of analysis in the latter period.