Amplification Tests Evaluated for Pelvic Inflammatory Disease

Sexually transmitted Chlamydia trachomatis (chlamydia) is the most prevalent sexually transmitted infection (STI) with an estimated 68,455,000 incident cases globally in women in 2012. Chlamydia is the subject of intensive control efforts in many high-income settings.

Nucleic Acid Amplification Tests (NAATs) are the recommended test type for diagnosing C. trachomatis; however, less sensitive diagnostic methods, including direct immunofluorescence (IF) and enzyme-linked immunoassay (ELISA), remain in use in lower resourced settings.

Danish and British scientists led by those at the Imperial College London (London, UK) extracted from the Denmark’s national Chlamydia Study dataset all chlamydia test records from women aged 15 to 34 years that were performed between January 1, 1998 and December 31, 2001, the interval when non-NAATs were replaced by NAATs as the most common test type. Tests were categorized as non-NAAT (IF/ELISA) or NAAT and limited to each woman’s first test in the study period. They linked test data to hospital presentations for pelvic inflammatory disease (PID) within 12 months.

The study included 272,105 women with a chlamydia test, just under half (44.78%) were tested using NAATs. Overall, 17,353 (6.38%) tested positive for chlamydia and 1,732 (0.64%) were diagnosed with PID within 12 months. The risk of PID following a positive chlamydia test did not differ by test type (NAAT 0.81%, non-NAAT 0.78%). The risk of PID following a negative test was significantly lower in women tested with NAATs compared to non-NAATs (0.55% compared to 0.69%). The team estimated that 18% of chlamydia infections in women tested with a non-NAAT were undiagnosed and that the risk of progression from undiagnosed chlamydia infection to PID within 12 months was 9.52%. The use of non-NAATs could lead to an excess of 120 cases of PID per 100,000 women tested compared to using NAATs.

The authors concluded that their retrospective observational study estimates the positive impact on women’s reproductive health from using accurate chlamydia diagnostic tests and provides further evidence for restricting the use of inferior tests. Women with a negative chlamydia test have a 17% higher adjusted risk of PID by 12 months if they are tested using a non-NAAT compared to a NAAT. The study was published on January 2, 2018, in the journal Public Library of Science Medicine.

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Imperial College London