Risk Factors for Community- and Household-Acquired Pertussis During a Large-Scale Outbreak in Central Wisconsin

Abstract

To identify risk factors associated with community- and household-acquired pertussis, we studied 61 households (HHs) with members with culture-positive illnesses and compared their characteristics with 58 neighborhood control-HHs and 62 randomly selected control-HHs. Case-HHs weremore likely than either control group to have members 12–18 y of age (P < .01); these individuals accounted for 34% of all primary cases. A history of exposure outside the home was the most important predictor of community-acquired infection (P < .001), with adolescents being at higher risk than other age-groups (odds ratio, 3.2; P < .001). After known exposure to a culture-positive case in the same HH, the risk of illness was unrelated to age; lengthy delays in initiating erythromycin therapy and prophylaxis were the only factors associated with secondary spread (P < .01). The risk of pertussis may be related more to the likelihood of exposure than to age-related increasesin susceptibility,and the risk can be reduced with appropriate use of erythromycin.