Background In July 2012, two Alberta Sexually Transmitted Infection (STI) Clinics changed their testing platform for rectal chlamydia (CT) from cell culture to nucleic acid amplification testing (NAAT). A significant increase in the proportion of rectal-only CT cases occurred after the introduction of NAAT (1.9%; n = 25 pre-NAAT vs. 20.1%; n = 245 post-NAAT, P < 0.001). We sought to examine the characteristics of rectal-only CT cases.
Methods All CT cases seen at two Alberta STI clinics between July 20 and December 31, 2012 were extracted from the provincial STI database. Variables included were demographics, clinical history, reasons for visit and site of infection. Cases positive from the rectum alone were compared with cases positive from urethra, cervix, vault and urine alone or in multiple sites including the rectum. CT testing was conducted with Genprobe Aptima by the Provincial Laboratory for Public Health. Univariate analysis was completed using Chi-square or Fisher’s exact test and Mann-Whitney for continuous variables. Bivariate logistic regression, adjusted for gender, was completed using significant (P > 0.05)at the univariate level.
Results Twenty percent of all CT cases (n = 245) were diagnosed in the rectum only; females were more likely to be diagnosed with rectal-only CT (24.6%) than males (16.6%; P = 0.001). No cases of rectal-only CT were found among heterosexual men; therefore regression models were completed for women and men who have sex with men (MSM). Factors associated with rectal-only CT for women included older age (AOR = 1.05, 95% CI: 1.02, 1.08), being tested at Clinic A (AOR = 3.0, 95% CI: 1.8, 5.1), and being named as a contact to an STI (AOR = 0.3, 95% CI: 0.1, 0.9). For MSM, being asymptomatic (AOR = 2.2, 95% CI: 1.2, 4.1) remained significant.
Conclusions After the switch to NAAT testing for rectal CT, additional cases of CT were found among women and MSM. Differences between clinics are likely attributable to different screening practises for women.
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