The prevalence of serum antibodies to Legionella pneumophila in patients with chronic pulmonary disease.

Sera from 113 outpatient with chronic pulmonary disease and 76 control subjects were tested by the indirect immunofluorescent technique for serum antibodies against Legionella pneumophila. No patient had an antibody titer greater than or equal to 1:256, a titer presumptive for past or present infection by Legionella pneumophila. However, 2 patients had a titer of 1:126, and 9 patients had a titer of 1:64. The control group (n = 76) had titers no higher than 1:32 (p less than 0.01). Eight of the 11 patients with a titer greater than 1:64 were from the subgroup of 41 patients with asthma (p less than 0.05), but this correlation was not attributable to corticosteroid therapy. Only 3 of 35 patients receiving corticosteroids at greater than replacement dosage had titers greater or equal to 1:64. The clinical significance of a single titer below 1:256, observed in 11 patients, is unknown.