Influence of endocervical specimen adequacy on PCR and direct fluorescent-antibody staining for detection of Chlamydia trachomatis infections

The cellular quality of the endocervical swab specimen used for the detection of Chlamydia trachomatis may dramatically impact the sensitivity of the diagnostic assay used. An evaluation of the adequacy of 319 endocervical swab specimens from women attending two inner-city sexually transmitted disease and family planning clinics, as well as five high school-based family planning clinics, was performed, and the resulting data were compared with the diagnostic results obtained by both Amplicor PCR and Microtrak direct fluorescent-antibody (DFA) staining. The swab from each patient was rolled across the open circular area of a DFA slide and then used to inoculate a transport tube for PCR (Roche), after which the swab was discarded. The slides were stained and examined by epifluorescence microscopy for the presence of C. trachomatis elementary bodies and for the presence and number of cell types to determine specimen adequacy. Cellular adequacy for a cervical swab specimen was defined as the presence of one or more columnar epithelial or metaplastic epithelial cells or the presence of more than 100 erythrocytes per high-power microscopic field. Of the 319 specimens read by DFA, 204 (63.9%) were determined to be adequate. There were 34 (10.7%) positive specimens by DFA and/or PCR. Twenty-nine (9.1%) specimens were positive by PCR, 20 (6.3%) specimens were DFA positive, and 15 (4.7%) were concordantly positive by both tests. The prevalence of chlamydia among adequate specimens was 14.2% (29/204), compared to 4.3% (5/115) for inadequate specimens (P < 0.0001). Variations in specimen quality and the sensitivity of the diagnostic assay used have a significant impact on determining the prevalence of C. trachomatis in a population.