Factors affecting urine EIA sensitivity in the detection of Chlamydia trachomatis in men

The significance of voiding interval before testing urine samples for Chlamydia trachomatis in men

OBJECTIVE

To investigate the effect of time since last urination on chlamydial positivity rates in men.

METHODS

Prospective study on men attending a genitourinary medicine clinic who were asked for the last time of their urination before obtaining their urine sample for testing for Chlamydia trachomatis with the Cobas Amplicor polymerase chain reaction (PCR) assay.

RESULTS

Of the total of 1649 men studied, 621 (37.6% (95% CI 35.3% to 39.9%)) had a voiding interval of less than 2 hours. There was no statistical evidence of a difference in the positivity rate of chlamydial infection among men with a voiding interval of less than 2 hours (106/621, 17.1%) and that of men with a voiding interval of 2 hours or longer (170/1028, 16.5%); difference in proportions 0.5% (95% CI to 3.2% to 4.3%), p = 0.779.

CONCLUSION

Voiding interval does not have a significant impact on the performance of the Cobas Amplicor PCR assay in men.

Noninvasive screening for genital chlamydial infections in asymptomatic men: Strategies and costs using a urine PCR assay

OBJECTIVE

To evaluate cost saving strategies to screen for genital chlamydial infection in men using polymerase chain reaction (PCR) technology.

METHODS

Men with no urethral symptoms presenting to a sexually transmitted disease (STD) clinic were recruited. Study participants underwent a questionnaire interview. Urethral swabs were taken to perform a smear for polymorphonuclear leucocytes (PMN) and for the detection of Chlamydia trachomatis by culture and PCR. First-catch urine was collected for a leukocyte esterase test (LET) and PCR.

RESULTS

C trachomatis infection was detected in 36 of 463 (7.8%) men. LET and PMN were positive in 10 (28%) and 12 (33%) infected men, respectively. Risk factors for chlamydial infection were younger than age 25 years, LET-positive, PMN-positive and STD contact (P<0.001). The direct cost of genital chlamydial infection in men in Canada has been previously estimated at $381/case. Based on a sensitivity of 90% for urine PCR, the estimated direct cost of testing all participants to detect 32 cases was $453/case. Using risk factors recommended in the Canadian STD Guidelines (age younger than 25 years, new partner, STD contact or unprotected sex), the same number of cases would have been detected by testing only 384 men at $376/case. Using age younger than 25 years or STD contact as the screening criterion, 78% of those infected would have been detected at $259/case, and no new cases would have been detected by adding LET-positive or PMN-positive as risk factors.

CONCLUSION

Targeted screening for chlamydial infection using urine PCR assay and risk factors recommended in the Canadian guidelines could substantially reduce the cost of screening at a STD clinic setting. LET and PMN smear did not appear to be useful indicators of chlamydial infection in this population.

Pooling of urine specimens for PCR testing: a cost saving strategy for Chlamydia trachomatis control programmes

OBJECTIVES

To evaluate pooling of first catch urine (FCU) specimens as a cost effective strategy for chlamydia testing.

METHODS

Mock specimens were pooled with and without dilution to determine optimal pool size and ease of work flow. The performance of the Amplicor Chlamydia trachomatis PCR assay on pooled specimens was compared with individual testing using 370 FCU specimens from asymptomatic men presenting to an STD clinic. Cost savings associated with pooling were estimated.

RESULTS

Using mock specimens, the sensitivity and specificity of the Amplicor PCR assay were not affected by pool sizes of two and five, but at a pool size of 10 decreased sensitivity due to inhibition was observed in one of five mock pools when the pooling method which involved no dilution was used. Archived FCU specimens from a study of 370 asymptomatic men were combined consecutively into 74 pools of five and tested by PCR. Of the 18 pools that contained positive specimens, 17 were PCR positive. Compared with testing FCU specimens individually, pooling resulted in a sensitivity of 95%, specificity of 100%, and a cost savings of 57% based on reduced number of tests required.

CONCLUSION

Depending on the prevalence of infection, pooling of FCU specimens for PCR testing may result in cost savings compared with testing specimens individually. Further evaluations to validate this strategy using fresh FCU specimens are needed.

Semen donors and STD screening

AIM

The British Andrology Society recommends screening semen donors for sexually transmitted infections to minimise the risk of pathogen transmission to the mother and fetus. The aim was to review recent findings of semen donor screening and, if appropriate, recommend changes to the screening protocol.

SUBJECTS

175 consecutive men attending for STD screening between January 1992 and December 1995 who had been preselected by the Department of Obstetrics and Gynaecology as suitable semen donors.

METHODS

Retrospective review of case notes and group comparison of demographic and sexual history data.

RESULTS

11 men (6%) had evidence of infection, excluding CMV seropositivity, at their first STD screen. After semen donation, 109 men (63%) were rescreened and, of these, 12% had positive findings. Positive findings at initial screening were predicted by a history of more than one partner in the preceding 6 months (OR 7.11, 95% CI 1.66-30.4) but it did not predict rescreening findings. Other factors such as age, marital status, employment status or past STDs were not predictive for either screen.

DISCUSSION

Less than 20% of initial volunteers meet the full criteria of high quality post-thaw semen, no transmissible genetic disorders, and no transmissible pathogens. Sexual history may predict but would not alone preclude all positive STD screening findings. It is essential that sequential STD screening of donors continues and that genitourinary physicians should be involved in this process. Validation of newer diagnostic techniques as screening tests in this setting is required.

Current methods of laboratory diagnosis of Chlamydia trachomatis infections

Infections caused by Chlamydia trachomatis are probably the most common sexually transmitted diseases in the United States. Commonly unrecognized and often inadequately treated, chlamydial infections can ascend the reproductive tract and cause pelvic inflammatory disease, which often results in the devastating consequences of infertility, ectopic pregnancy, or chronic pelvic pain. C. trachomatis infections are also known to increase the risk for human immunodeficiency virus infection. The obligate intracellular life cycle of C. trachomatis has traditionally required laboratory diagnostic tests that are technically demanding, labor-intensive, expensive, and difficult to access. In spite of these historical challenges, however, laboratory diagnosis of C. trachomatis has been a rapidly advancing area in which there is presently a wide array of commercial diagnostic technologies, costs, manufacturers. This review describes and compares the diagnostic methods for C. trachomatis infection that are currently approved for use in the United States, including the newest DNA amplification technologies which are yet to be licensed for commercial use. Issues to consider in selecting a test for purposes of screening versus diagnosis based on prevalence, performance, legal, social, and cost issues are also discussed.

Diagnosis of Chlamydia trachomatis infections in asymptomatic men and women by PCR assay

A PCR assay was evaluated for its ability to detect genital chlamydial infection in asymptomatic men and women. Urethral swab specimens were collected from 472 men for culture and PCR assay, and first-void urine (FVU) specimens were collected from 379 of these men for enzyme immunoassay (EIA) and PCR assay. Cervical swab specimens were collected from 242 women for culture, EIA, and PCR assay. Patients were considered infected if they were culture positive or positive by PCR with both plasmid- and major outer membrane protein-based primers. By using this extended "gold standard," the prevalence of infection in this population was 7.6% for men and 7.9% for women. For men, the sensitivities of urethral swab specimen culture and PCR and FVU specimen EIA and PCR were 61, 72, 55, and 91%, respectively. All assays had specificities of > or = 99.8%. The positive and negative predictive values for PCR testing of FVU specimens were 100 and 99.4%, respectively, compared with values of 96.3 and 97.8%, respectively, for PCR of urethral swab specimens. The sensitivities of cervical swab specimen culture and PCR testing were 42 and 90%, respectively, with corresponding specificities of 100 and 99.3%. All cervical swabs were negative by EIA. Molecular techniques such as PCR assays are valuable tools for the detection of symptomatic genital chlamydial infection. In particular, PCR assays of FVU specimens from men offer a highly sensitive, noninvasive screening tool that will likely improve patient compliance for diagnostic testing.