Diagnóstico molecular das infecções por Chlamydia trachomatis e ...

ABSTRACT
Background: The introduction of the nucleic acid amplification tests (NAATs) was a
major breakthrough in the screening for the sexually transmitted diseases (STD)
caused by Chlamydia trachomatis and Neisseria gonorrhoeae because they are
highly sensitive and they can be used with noninvasive specimens, such as urine.
The use of urine has made it far easier to test asymptomatic individuals and has also
made it possible to perform epidemiological studies in places other than clinical
settings. Many studies have shown also that vaginal swab can be used for detection
of both infections, however, just the NAAT Aptima Combo 2 has been cleared by
Food and Drug Administration for this specimen use. In Brazil, the most widely used
NAAT for the diagnosis of chlamydia and neisseria is the kit Amplicor CT/NG (Roche)
and, up to date, there isn’t any study which evaluates the use of vaginal swabs.
Objectives: To evaluate the performance of the kit AMPLICOR CT/NG (Roche) in
the diagnosis of C. trachomatis and N. gonorrhoeae using urine, endocervical and
vaginal swabs and to analyze the agreement of results between the different
biological specimens. Methods: The target population was sexually active
adolescents and young women between 15 and 24 years from Inhumas, Goias.
Socio-demographic and sexual behavior were obtained through a face-to-face
interview. The diagnosis was performed by PCR using the AMPLICOR CT/NG
(Roche) assay in urine, vaginal swab (VS) and endocervical swab (ES) specimens.
For the performance evaluation were calculated the sensitivity, specificity, positive
predictive value and negative predictive value. The kappa coefficient was calculated
to assess agreement between the samples. It was considered a true-positive result
when at least two of three biological samples from the same patient were positive for
chlamydia and/or gonococcus. Results: Among the 428 participants the mean age
was 19,4 years. The three biological specimens were collected from 309 adolescents
(72.2%). Among these, the prevalence rates were 8.7% (IC95% 5,8-12,4) for C.
trachomatis and 2.3% (IC95% 0,9-4,6) for N. gonorrhoeae. For chlamydia the
sensitivities observed with the different samples were above 80% and specificities
exceeding 97% with positive predictive values (PPV) between 78.8% and 84.6% and
negative predictive values (VPNs) >98%. For the gonococcus the sensitivities were
42.8% for urine, 71.4% for ES and 100% for VS with specificities >96% for the three
samples. The two types of swab showed low PPVs for gonococcus (≈40%) and urine
showed PPV of 100%. VPNs were >98%. The agreement of results between
specimens was around 94% for the detection of both infections. However, the values
of kappa (κ) coefficient ranged from 0.68 to 0.73 for chlamydia, which means
substantial agreement between samples. For gonococcal infection, the agreement
was slight or fair with κ coefficients ranging from 0.13 to 0.33. Conclusions: The
performances of the specimens and the κ values suggest that the vaginal swab
appears to be equivalent to urine and endocervical swab for detection of chlamydia
and may be suitable for screening studies. The three samples showed different
performance in the detection of gonococcus and did not present good agreement of
results, suggesting that they are not equivalent in the diagnosis of this infection with
the PCR kit used.
Key-words: C. trachomatis, N. gonorrhoeae, prevalence, urine, endocervical swab,
vaginal swab, PCR, performance.
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