Use of Polymerase Chain Reaction in an Epidemiologic Investigation of Pontiac Fever

In June 1992, 13 (38%) of 34 resort guests experienced illness that met a symptom-based case definition of Pontiac fever. Each ill guest reported using an indoor hot tub compared with 6 (29%) of 21 nonill guests (P < .001). Water samples from the indoor hot tub were culture-negative for legionellae using standard techniques, coculture with amebae, and intraperitoneal inoculation of guinea pigs. However, polymerase chain reaction (PCR) testing of the water samples indicated the presence of Legionella pneumophila. Direct fluorescent antibody testing identified the organism as serogroup 6. Seroconversion to L. pneumophila serogroup 6 occurred in 7 (64%) of 11 ill guests and none of 5 nonill guests (P = .03). These results suggest that in certain circumstances, culture of environmental samples should be supplemented with additional tests such as PCR. These results are also consistent with the concept that Pontiac fever can be caused by nonviable legionellae.