A major strength of our study was our ability to follow up patients prospectively who had little opportunity for a sexual encounter before their TOC. The authors of previous studies relied on patient report of condom use and/or abstinence to account for cases of reinfection.5,7,8,21 Other strengths of our study include our ability to provide directly observed therapy. We performed TOCs at an average of 4 weeks to decrease the likelihood of residual chlamydia rRNA as the estimated clearance occurs at day 17 (rRNA was detectable in 21% of women 14 days after treatment for chlamydia).22 One study citing azithromycin efficacy of 77.4% sent TOCs at 2 weeks after treatment.7 The major limitation of our study is the inability to genotype the specimens to ensure treatment failure. Genotyping was not available in our laboratory. Another limitation of the study is lack of inquiry about interim sexual contact to exclude reinfection, but this is highly unlikely given private rooms, close monitoring, and sex separation. In addition, our participants were mostly asymptomatic adolescents; symptomatic patients may have a different failure rate. Finally, we used urine samples to test for chlamydia infections in young men and women. Because vaginal swabs have a higher sensitivity and specificity compared with urine samples in women, we may have underestimated the number of chlamydia infections and subsequent treatment failures in women.10 One important additional finding of the study was the high report of abdominal pain (35%) with administration of azithromycin. Four percent of our participants vomited. Our results suggest that physicians should recommend that patients take medication with food and warn of associated abdominal pain and potential vomiting necessitating additional medication. Our findings support previous studies identifying definite treatment failures with the use of azithromycin in treatment of uncomplicated C. trachomatis; however, azithromycin remained effective in our population. Further research studying the etiology of azithromycin treatment failure and its risk factors in other patient populations is needed to confirm our findings.
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