THREE YEARS' EXPERIENCE OF SERODIAGNOSIS OF LEGIONELLA PNEUMOPHILA INFECTIONS

During a three-year-period, serum samples from 209 patients with acute pneumonia were tested for antibodies to Legionella pneumophila, using an indirect micro-immunofluorescent antibody test performed with heat-killed serogroup specific antigens. Low antibody levels, defined by titres ranging from 32 to 128, were demonstrated in 73 of the patients. Seroconversion indicating current L. pneumophila, Serogroup 1, infection was documented in 3 previously healthy individuals. High IgM antibody titres suggested such an infection in 3 other patients. Thirteen patients showed either static or single antibody titres of 256 or greater. Only 7 of these patients had antibodies detectable with formalin-inactivated L. pneumophila, Serogroup 1, antigen. The high frequency of stationary antibody titres to heat-inactivated L. pneumophila antigen found in the present study suggests that formalin-inactivated organisms may be a superior antigen for the serodiagnosis of current Legionnaires' disease.