A recurrent outbreak of nosocomial legionnaires' disease detected by urinary antigen testing: Evidence for long-term colonization of a hospital plumbing system

BACKGROUND: In 1994, a hospital reported an increase in nosocomial legionna ires' disease after implementing use of a rapid urinary antigen test for Le gionella pneumophila serogroup 1 (Lpl). This hospital was the site of a pre vious nosocomial legionnaires' disease outbreak during 1980 to 1982. METHODS: Infection control records were reviewed to compare rates of nosoco mial pneumonia and the proportion of cases attributable to legionnaires' di sease during the 1994 outbreak period with those during the same period in 1993. Water samples were collected for Legionella culture from the hospital 's potable water system and cooling towers, and isolates were subtyped by m onoclonal antibody (MAb) testing and arbitrarily primed polymerase chain re action (AP-PCR). RESULTS: Nosocomial pneumonia rates were similar from April through October 1993 and April through October 1994: 5.9 and 6.6 per 1,000 admissions, res pectively Gate ratio [RR], 1.1; P=.56); however, 3.2% of nosocomial pneumon ias were diagnosed as legionnaires' disease in 1993, compared with 23.9% in 1994 (RR, 9.4; P<.001). In 1994, most legionnaires' disease cases were det ected by the urinary antigen testing alone, MAb testing and AP-PCR demonstr ated identical patterns among Lpl isolates recovered from a patient's respi ratory secretions, the hospital potable water system, and stored potable wa ter isolates from the 1980 to 1982 outbreak. CONCLUSIONS: There may have been persistent transmission of nosocomial legi onnaires' disease at this hospital that went undiscovered for many years be cause there was no active surveillance for legionnaires' disease. Introduct ion df a rapid urinary antigen test improved case ascertainment. Legionella species can be established in colonized plumbing systems and may pose a ri sk for infection over prolonged periods