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 with a neutralizing reagent below the cutoff of the Chlamydiazyme enzyme immunoassay represent infected patients, we used direct fluorescent-antibody staining for elementary bodies (EBs) and PCR to confirm results for cervical swabs collected from 55,963 women and urethral swabs or first-void urine (FVU) samples collected from 5,781 men attending physicians' offices in the Toronto, Canada, area. Within a grey zone arbitrarily selected 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 more 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 results for male specimens were 6 of 6 urethral swabs and 17 of 18 FVU samples. Application of the blocking test to specimens negative in the Chlamydiazyme enzyme immunoassay but having optical densities within 40% of the cutoff added 14.2% (217 of 1,531 specimens) more positive results to the survey. A total of 213 of 217 samples (98.2%) were reconfirmed as having EBs or DNA.
Krepel
J
J
Department of Microbiology, Gamma North Peel Laboratory, North York, Ontario, Canada.
Laur
I
I
Sproston
A
A
Luinstra
K
K
Jang
D
D
Mahony
J
J
Chernesky
M
M
D000293:Adolescent; D000328:Adult; D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial / Q000302:isolation & purification*; D002690:Chlamydia Infections / Q000175:diagnosis*; D002692:Chlamydia trachomatis / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D005189:False Positive Reactions; D005260:Female; D052776:Female Urogenital Diseases / Q000175:diagnosis*; D019085:Fluorescent Antibody Technique, Direct / Q000379:methods*; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D052801:Male Urogenital Diseases; D016133:Polymerase Chain Reaction / Q000379:methods*; D013048:Specimen Handling; D014526:Urethritis / Q000382:microbiology; D002575:Uterine Cervicitis / Q000382:microbiology
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial