EXPANDED GOLD STANDARD IN THE DIAGNOSIS OF CHLAMYDIA-TRACHOMATIS IN ALOW-PREVALENCE POPULATION - DIAGNOSTIC EFFICACY OF TISSUE-CULTURE, DIRECT IMMUNOFLUORESCENCE, ENZYME-IMMUNOASSAY, PCR AND SEROLOGY

Objective-To evaluate the diagnostic efficacy of chlamydia culture, di rect immunofluorescence (DFA), direct enzyme immunoassay (EIA), polyme rase chain reaction (FCR) and serology by defining positive culture or at least two positive non-culture tests as true positive. Setting-Thr ee gynaecological departments located in separate areas of Sweden. Pat ients and Design-All pregnant women requesting abortion during a six m onth period were included. In cases with unconfirmed non-culture tests , reculture with multiple passage and PCR on the culture transport med ium was performed for confirmation. Serum was analysed for chlamydial antibodies type IgG, IgM and IgA using microimmunofluorescence. Result s-18 of 419 (4.3%) patients were positive for chlamydia according to t he defined criteria. Twelve of 419 (2.9%) were positive in standard cu lture (primary inoculation). The sensitivity of standard culture, DFA, EIA and PCR were 66.7%, 77.8%, 64.7% and 71.4% respectively. The spec ificity 100% (by definition), 99.5%, 100%, 100% respectively. The posi tive predictive value 100% (by definition), 87.5%, 100%, 100% respecti vely. Negative predictive value 98.5%, 99.0%, 98.5%, 98.9% respectivel y. Serum IgG titre of greater than or equal to 64 and greater than or equal to 1024 gave positive predictive values of 10% and 21% respectiv ely. Conclusions-When an expanded gold standard is used, the specifici ty and positive predictive value of the non-culture tests used are com parable with that of standard culture even in this low prevalence popu lation. Standard culture underestimated the chlamydia prevalence by 33 %. The prevalence found represents a decrease from 10 to 2.9% of cultu re verified chlamydia during four years in comparable populations. Chl amydial antibodies of certain immunological classes are not necessaril y present in cases with chlamydia.