Literature reviews  >  Articles for review > Marrazzo et al. Impact of patient characteristics... 

Nucleic acid amplification assays are useful for screening and diagnosis of C. trachomatis in diverse clinical populations of women.

Impact of patient characteristics on performance of nucleic acid amplification tests and DNA probe for detection of Chlamydia trachomatis in women with genital infections.
Marrazzo JM, Johnson RE, Green TA, Stamm WE, Schachter J, Bolan G, Hook EW III, Jones RB, Martin DH, St. Louis ME, Black CM.
Journal of Clinical Microbiology 2005;43:577-584
 
Summary:

Question

How do clinical and demographic characteristics affect the sensitivity and specificity of nucleic acid amplification tests (NAAT) compared to non-NAAT among women attending family planning and STD clinics?

Design

The impact of age, endocervical and urethral inflammation, and menstrual blood on the performance of NAAT versus an unamplified DNA probe assay were evaluated using an expanded and independent diagnostic reference standard in a large, diverse population of women attending family planning and STD clinics at five centers. 

Participants

Women (n = 3551) presenting to STD clinics at five centers (76.5% of participants) and one family planning clinic (20.7% of participants) who were at least 16 years old, not pregnant, and had not taken antibiotics in the previous 30 days were tested. The median age was 24 years, 30.6% were between 20 and 24 years old, and 63.4% were black.

Description of Tests and Diagnostic Standard

Each woman collected a 30 ml urine specimen for testing by ligase chain reaction (LCR, LCx, Abbott Laboratories, Abbott Park, IL) and polymerase chain reaction (PCR, Amplicor, Roche Diagnostic Systems, Branchburg, NJ). A urethral swab was collected for C. trachomatis culture on McCoy cells. After incubation for 48 to 72 h, the cells were stained with C. trachomatis outer membrane protein-specific fluorescein-conjugated antibody reagents. Endocervical swabs were collected for Gram stain and culture for N. gonorrhoeae and in a random order for LCR, PCR, and PACE2 (Gen-Probe), a DNA probe assay. An endocervical cytobrush was collected for C. trachomatis culture. C. trachomatis and N. gonorrhoeae cultures were performed according to each center's usual protocol. Commercial nonculture tests were performed according to the manufacturers' instructions, except that repeat LCR tests due to equivocal results on initial testing were performed on specimens that had been frozen for up to several weeks and M4 transport medium was used for the PCR cervical test. Urine was tested for the presence of blood and leukocyte esterase performed by dipstick scored as negative, trace, or 1+ to 4+.A result >1+ was considered positive. A two-specimen reference standard (patient standard), in which subjects were classified as infected with C. trachomatis if any reference test at any anatomic site was positive, was used to determine the performances of the LCR, PCR, and PACE2 assays.

Main Outcome Measures

The sensitivity and specificity of LCR, PCR, and PACE2 in the presence or absence of key subject characteristics were calculated. Characteristics included age, presence of mucopurulent endocervical discharge, report of concurrent menses, concurrent cervical infection with N. gonorrhoeae, and signs and symptoms of urethral inflammation (dysuria and blood or leukocyte esterase in the urine). The relative increases in detection of positives by cervical and urine NAAT compared to cervical PACE2 were calculated.

Main Results

The overall prevalence of C. trachomatis among the 3551 women was 15.1% as measured by the patient standard. Chlamydia positivity was highest among adolescents (27.2%), women with mucopurulent cervical discharge (30.1%), women with a positive N. gonorrhoeae culture (36.5%), and women who reported contact with a sex partner with a C. trachomatis (43.7%) or N. gonorrhoeae (28.8%) infection. When C. trachomatis positivity was stratified by test type and clinical characteristics, LCR and PCR were significantly (P < 0.05) more positive at the cervix than PACE2 except when the patient had concurrent menses or positive N. gonorrhoeae culture. In these cases, the LCR detected more positives than PCR or PACE2.LCR was more positive at the cervix than PCR except when the patient had mucopurulent cervical discharge. LCR and PCR gave similar results for urine specimens. For all cervical tests, NAAT positivity did not differ in women who reported concurrent menses relative to those who did not.

On average, use of a NAAT to test cervical or urine specimens resulted in an increase of positivity over PACE2 of 33%.High relative increases in positivity over PACE2 were seen when the LCR was used to test cervical specimens from women who did not have mucopurulent discharge (46%), and whose urines were negative for blood (51%) and leukocyte esterase (45%).The relative increase in detection by cervical PCR over PACE2 was higher among women >20 years old than among younger women (31 versus 19%). The highest relative increase over PACE2 using a NAAT to test urine was seen with LCR among women reporting dysuria (73%).

The sensitivity and the specificity the 3 nonculture assays for testing cervical specimens and the sensitivity and the specificity of the 2 NAAT for testing urine specimens for detection of C. trachomatis infection as determined by the patient standard are shown in the table.The performance of each test is determined using a reference standard based on two other tests. Cervical PCR sensitivity was significantly higher among women with mucopurulent endocervical discharge (83.9%) than among those without discharge (71.1%).Cervical LCR sensitivity was significantly higher among women infected with N. gonorrhoeae (91.2%) than among those not infected (81.0%).The sensitivities of both NAAT when performed on urine specimens were significantly higher among women with a positive urine leukocyte esterase test (86.3 and 81.5%) compared to women with a negative test (69.7% and 61.5%). 

Sensitivity and specificity of PACE2, LCR, and PCR performed on cervical specimens and of LCR and PCR performed on urine specimens for detection of C. trachomatis as determined by a patient standard among 3551 women

Authors' Conclusions

The presence of endocervical or urethral inflammation was associated with higher sensitivities of NAAT. Concurrent menses had no effect on the performance of either cervical or urine NAAT or on cervical PACE2. Urine and cervical NAAT afforded the highest relative increase in detection of C. trachomatis in women who were most likely to have lower burdens of infection. These findings support the use of urine and cervical NAAT for screening and diagnosis of C. trachomatis infections in diverse clinical populations of women.

Source of funding: Centers for Disease Control and Prevention cooperative agreement

For correspondence: Jeanne M. Marrazzo, MPH, Harborview Medical Center, Division of Infectious Diseases, 325 Ninth Ave., Mailbox 359931, Seattle, WA 98104.E-mail address: jmm2@u.washington.edu

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