Diagnosis of chlamydial and gonococcal conjunctivitis: performance evaluation of a nucleic acid amplification test

No regulatory agency-approved nucleic acid amplification tests (NAATs) exist for detecting Chlamydia trachomatis (CT) or Neisseria gonorrhoeae (NG) in conjunctival samples, necessitating validation, including performance analysis. This is challenging due to case rarity and the absence of a gold standard. This retrospective case series evaluated the performance of the Roche cobas CT/NG NAAT on conjunctival samples using microbiological and clinical data. Clinical records of patients with positive CT/NG NAAT conjunctival samples processed in our laboratory between 2013 and 2023 were reviewed, along with matched negative controls. Positive results were confirmed using a stepwise algorithm: (i) positive NG culture (NG only); (ii) confirmatory CT/NG NAAT performed at the Laboratoire de santé publique du Québec (LSPQ); (iii) CT/NG NAAT from other anatomical sites; or (iv) clinical presentation compatible with CT/NG conjunctivitis. Negative controls were confirmed based on clinical information. Sixty-five positive conjunctival samples were included (53 CT-positive, 12 NG-positive). Of the 53 CT-positive samples, 52 were confirmed (21 by LSPQ testing, five by a concomitant genital sample, and 26 by a compatible presentation). Of 53 CT-negative controls, 45 were clinically confirmed as true negatives. Among the 12 NG-positive samples, 11 were confirmed (seven by culture, four by LSPQ testing). Of 12 NG-negative controls, 11 were clinically confirmed. Sensitivity and specificity were 87% and 98% for CT, and both were 92% for NG. Given sufficient data, the Roche cobas CT NAAT assay on conjunctival samples does not require confirmatory testing. However, confirmation of NG-positive results should continue until more data are available.

Chlamydia trachomatis (CT) conjunctivitis has been increasingly observed in adults and neonates. If untreated, it can cause local complications and, in adults, contribute to ongoing transmission. Neisseria gonorrhoeae (NG) conjunctivitis is rarer, but its hyperacute presentation can lead to severe outcomes, such as orbital cellulitis or globe rupture. Conventional diagnostic methods for CT are either unavailable or highly resource-consuming, and NG culture lacks sensitivity, underscoring the need for rapid and reliable diagnostic methods. Nucleic acid amplification tests (NAATs) are considered the gold standard for detecting CT and NG in urogenital, pharyngeal, and rectal sites, due to their high sensitivity and specificity. Despite widespread use on conjunctival specimens, no NAAT is approved by regulatory agencies. Evaluation of the Roche cobas CT/NG assay is crucial to establish its performance on conjunctival specimens and to provide clinicians with accurate, timely diagnostic results.