Helms C M, Johnson W, Renner E D, Hierholzer W J, Wintermeyer L A, Viner J P
Infect Immun. 1980 Nov;30(2):612-4. doi: 10.1128/iai.30.2.612-614.1980.
The background prevalence of microagglutination antibodies to Legionella pneumophila was determined by testing the sera of 517 individuals who lived or worked in a small Iowa town. In this population, the upper limit of normal microagglutination titer for serogroups 1, 3, and 4 was 1:16, and that for serogroup 2 was 1:8. The prevalence of microagglutination titers of greater than or equal to 1:32 against any serogroup of L. pneumophila was only 7.4% and did not vary significantly with age or sex.