Legionnaires' disease: the epidemiology of two outbreaks in Burlington, Vermont, 1980

Eighty-five cases of Legionnaires' disease were diagnosed in two major outbreaks at a large regional medical center in Burlington, Vermont, in the summer of 1980. Cases in both outbreaks were positive for Legionella pneumophila, serogroup 1 by culture, serology, or direct fluorescent antibody tests. All cases had spent time in the city of Burlington in the 10 days before the onset of symptoms. Cases in both outbreaks were both hospital- and community-acquired. A case-control study identified no common in-hospital exposure, including shower use, that was associated with illness. Cases without previous exposure to the hospital were more likely to occur in persons with residences in neighborhoods just downwind of cooling tower A, but not throughout the municipal water system. Epidemiologic and environmental studies supported the association of this cooling tower, located 150 m from the hospital, with both outbreaks. Maintenance employees who worked with tower A had higher Legionella titers than those who worked with a comparison tower located 1.6 km away. Aerosolization of L. pneumophila by tower A and airborne spread to the hospital and community are postulated. The distance of airborne transmission of L. pneumophila in these consecutive outbreaks is greater than previously reported.