Prevalence of Legionella pneumophila serogroup 1 antibodies in blood donors.

The prevalence of anti-Legionella pneumophila serogroup 1 antibodies in 777 blood donors of the Turin area was determined by the indirect immunofluorescence assay (IFA) and by the microagglutination test (MA). Low titers (IFA of 1/16 and MA of 1/8) were found in 0.3% of the subjects. A statistically significant difference was not observed by sex and by age for IFA titers, but was noted by sex for MA titers of > or = 1/4 (p < 0.05). The upper limit of normal titer was < 1/8 by IFA and < 1/4 by MA at 15% cutoff level and 1/8 by IFA and 1/4 by MA at 1% cutoff level. In conclusion, the prevalence of antibodies in the Turin area was very low; IFA titers of > or = 1/64 and MA titers of > 1/16 can be considered as presumptive of infection in a single serum specimen of a patient with pneumonia; no change in the epidemiology of the disease was observed in the recent years.