QUANTIFICATION OF CHLAMYDIA-TRACHOMATIS IN CERVICAL AND URINE SPECIMENS FROM WOMEN ATTENDING A GENITOURINARY MEDICINE CLINIC - IMPLICATIONSFOR SCREENING STRATEGIES

Population screening and intervention programmes can reduce the preval ence and incidence of infection with Chlamydia trachomatis, especially if sensitive molecular diagnostic tests are used. However, diagnostic tests that perform well on genitourinary medicine (GUM) clinic popula tions may be less useful for screening, particularly if the majority o f infected subjects are asymptomatic and their samples contain fewer o rganisms. We have compared the extent of low organism load in cervical and urine samples from symptomatic and asymptomatic chlamydia-positiv e women, by using a direct fluorescent antibody staining method and co unting the chlamydial elementary bodies (EBs). We have investigated th e ability of an enzyme immunoassay (EIA; MicroTrak) and a DNA amplific ation (Ligase chain reaction; LCR) assay to detect low numbers of orga nisms in cervical samples and the ability of the LCR assay to detect l ow numbers of organisms in urine. A low organism load (<10 EBs) was se en by direct fluorescent antibody (DFA) staining in about 30% of cervi cal samples and in about 75% of urines from chlamydia-positive women; the proportions in symptomatic women were not significantly different from those in asymptomatic women. The ELA identified only 16% of cervi cal samples that contained <10 EBs by DFA staining; the LCR identified 100% of cervical samples and 93% of urine samples that contained <10 EBs by DFB staining. The findings suggest that the ability of chlamydi al diagnostic tests to identify positive women should be similar among patients attending a GUM clinic and those taking part in a population screening programme, and that sensitive molecular assays such as the LCR should identify subjects with a low organism load in both groups.