Pontiac fever at a sewage treatment plant in the food industry

Background and objectives During a hot and humid summer period workers beca me ill with fever and flu-like symptoms after repairing a decanter for slud ge concentration at a sewage treatment plant. The work took place over a pe riod of 10 days in a small closed room, while another decanter was in opera tion and was consequently emitting aerosol to the environment, to which the workers were exposed. The aim of this study was to determine the cause of this outbreak of febrile illness so that additional cases could be prevente d. Methods All 5 patients were seen and examined in the Department of Occupati onal Medicine. Furthermore 2 of the workers had recurrent illness and were examined during hospitalization. As Pontiac fever (nonpneumonic legionellos is) was suspected, antibodies to legionellae were measured in blood samples . After positive antibody titers to Legionella pneumophila were found, samp les of the sludge were collected for legionellae culture. Results and conclusions The clinical picture agreeed with that described fo r Pontiac fever, and positive antibody titers to L pneumophila serogroup 1 were found in blood from all 5 patients. L pneumophila serogroup 1 was cult ured in high amounts from sludge from the decanter. It was concluded that t he fever was caused by L pneumophila emitted to the environment by the unco vered decanter. Procedures for preventing new cases were established.