PCR AND DIRECT FLUORESCENT-ANTIBODY STAINING CONFIRM CHLAMYDIA-TRACHOMATIS ANTIGENS IN SWABS AND URINE BELOW THE DETECTION THRESHOLD OF CHLAMYDIAZYME ENZYME-IMMUNOASSAY

In order to test the hypothesis that specimens blocking,vith a neutral izing reagent below the cutoff of the Chlamydiazyme enzyme immunoassay represent infected patients, we used direct fluorescent-antibody stai ning for elementary bodies (EBs) and PCR to confirm results for cervic al swabs collected from 55,963 women and urethral swabs or first-void urine (FVU) samples collected from 5,781 men attending physicians' off ices in the Toronto, Canada, area. Within a grey zone arbitrarily sele cted to represent values up to 40% below the positive threshold of the test run, 134 cervical swabs, 44 urethral swabs, and 39 FVU specimens exhibited a blocking response (>50% reduction in signal). Three or mo re EBs were observed in each of 98 cervical swabs (73.1%), 38 urethral swabs (86.4%), and 21 FVU specimens (53.8%). Of the 36 cervical swabs with fewer than three EBs, 33 were PCR positive; the positive PCR res ults for male specimens were 6 of 6 urethral swabs and 17 of 18 FVU sa mples. Application of the blocking test to specimens negative in the C hlamydiazyme enzyme immunoassay but having optical densities within 40 % of the cutoff added 14.2% (217 of 1,531 specimens) more positive res ults to the survey, A total of 213 of 217 samples (98.2%) were reconfi rmed as having EBs or DNA.