Rapid risk assessment: Chlamydia trachomatis false-negative test results by Aptima Combo 2 CT/NG assay (Hologic) in the EU/EEA, 2019

Risk assessment

In April 2019, Finland reported false-negative or equivocal results in patients tested for Chlamydia trachomatis (CT) using Aptima Combo 2 Assay (Hologic) (AC2). From February–May 2019, over 190 specimens that tested negative and/or equivocal with AC2 (targeting the 23S rRNA gene) of 2 314 specimens also tested positive with Aptima CT Assay (ACT) (targeting the 16S rRNA gene).

Executive summary

A patient tested in June 2018 has been identified as the earliest case with discordant results. In laboratories using AC2 in Finland, the cases that may have been missed due to false-negative or equivocal results may amount to 6–10% of CT positive cases. 

In mid-May 2019, Hologic confirmed that a mutation in the 23S rRNA gene is the likely root cause of the discordant results and issued an Urgent Field Safety Notice in June 2019 with updated instructions for test result interpretation and reflex testing of samples to laboratories using AC2. The implementation of these measures will allow for the appropriate diagnosis and management of the variant CT. 

Two samples in Sweden have been confirmed as having the 23S rRNA gene mutation. At the time of issuing this risk assessment, additional Member States are investigating discordant AC2/ACT results.