A pseudo-outbreak of Chlamydia trachomatis in a state residential facility: implications for diagnostic testing.

In December 1998, an outbreak of Chlamydia trachomatis genital infections was reported among 18 residents of a state residential facility housing 392 mentally retarded clients. The initial patient tested positive by ligase chain reaction (LCR); 17 others tested positive by culture. Serologic test results for C. trachomatis antibodies in patients who had tested positive by culture were negative. Further testing showed that C. trachomatis DNA could not be detected in the LCR specimen or in any reportedly positive culture specimens. At the original culture laboratory, C. trachomatis culture was infrequently performed, and positive controls were not adequately prepared. This pseudo-outbreak highlights problems that may occur with C. trachomatis testing. As experience with C. trachomatis culture declines, laboratories performing this test should ensure quality and consider confirmatory testing. For C. trachomatis screening tests, the need for confirmatory testing depends on individual patient considerations (including medical-legal implications) and prevalence of infection in the tested population.