Prevalence of positive antibody response in two residential populations with different legionella contamination in their hot-water system

Only Few epidemiological data on legionella diseases are available in Germany and studies on the prevalence of legionella antibody response in the population are scarce. We report on an epidemiological study on immune response in residents of homes with heavy and with minor legionella contamination in their hot-water system. 53 inhabitants of houseblocks with central hot-water system and high legionella contamination (6,049 +/- 17,995 cfu/l: 40 % > 1,000 cfu/l) were studied. 92 persons living in 1-2 family houses with decentral hot water systems (244 +/-1.434 cfu/l; 3%>1,000 cfu/l) served as controls. All persons filled in a questionnaire on bronchial and fever diseases etc; blood specimen were tested for legionella antibodies (different methods: immunofluorescence, and ELISA), and urine specimens were analysed for legionella antigen. During this investigation in the population exposed to Legionella no cases of legionellosis were reported. The prevalence of legionella antibodies was twice as high in the exposed versus the control persons. Significant correlation between cfu/l and legionella antibody titer in the inhabitants were found. One person with high antibody titer and with legionella-free hot-water system in his home had reported about pulmonary problems after having stayed in a hotel. The positive antibodies of the other persons are most likely the result of asymptomatic infections caused by permanent exposure in their home hot-water supply. In conclusion, with regard to the increased prevalence of antibody titers against legionellae in the exposed inhabitants and the significant correlation between antibody titers and cfu/l in hot-water samples, the necessity to control and redevelop hot-water systems in homes is confirmed - even though no cases of legionelloses in the exposed population were reported.