New implications for institutional outbreaks of Mycoplasma pneumoniae

Background: Outbreaks of Mycoplasma pneumoniae infection occur occasionally in institutional settings. In summer 1996, we investigated a large such outbreak among students at a Federal Service Academy. Methods: Throat swabs and serum samples were obtained for testing by polymerase chain reaction (PCR), culture and serology. Cohort and nested case-control studies were done to identify risk factors for acquisition of disease. Results: During the 2 month outbreak, 164/233 (70%) freshmen and 154/354 (44%) upperclassmen questioned reported having a respiratory illness consistent with M. pneumoniae infection. Of the 119 ill students who had complete laboratory evaluation, 65 (55%) had laboratory evidence of M. pneumoniae infection. The first phase of the outbreak involved freshmen; the second, occurring 2-3 weeks later, involved predominantly upperclassmen, who had arrived on campus 2 weeks after the freshmen. In multivariate analysis of the first phase, ill students were more likely than well ones to have multiple visits to the academy's health clinic before the onset of respiratory illness (OR=1.4,95% CI=1.1-1.7). A case-control study of freshmen visiting the health clinic showed that transmission was more likeiy when more than 6 people were present in the waiting room (OR=20.6, CI=1.9-530). Of 7 students with PCR-positive specimens during the acute-phase of illness who were men treated with azithromycin or clarithromycin, all 7 had negative repeat PCR results 4-19 days after finishing the antibiotic course. Conclusions: Crowding in the health clinic was a significant risk factor for M. pneumoniae infection in this outbreak. A separate waiting room for patients with respiratory symptoms during an outbreak of M. pneumoniae may limit transmission. Although the numbers in this study were small, it suggested mat the newer macrolide antibiotics, unlike erythromycin and tetracyclines, may eliminate carriage and therefore limit transmission during outbreaks of M. pneumoniae.