LAUSR

BACKGROUND The Aptima Combo 2® (AC2) assay manufactured by Hologic, Inc. detects Neisseria gonorrhoeae (NG) and/or Chlamydia trachomatis (CT) in urogenital and extragenital specimens by targeting either a 16S rRNA (NG) or 23S rRNA (CT) region. In 2019, a mutation (C1515T) in the 23S rRNA region was reported to cause false negative/equivocal results in specimens collected in Finland. Specimens containing this variant (Fl-nvCT) were also discovered internationally. Working with specimens submitted to a large commercial laboratory, we sought to determine if this variant was also present in the United States. METHODS A subset (N = 401) of specimens tested with the AC2 assay collected during a five-week period in late 2019/early 2020 were evaluated using an updated AC2 assay. RESULTS While the FI-nvCT variant was not detected within this specimen panel, two CT variants containing 23S rRNA mutations (A1518G, G1526A) were identified. The updated AC2 assay targeting an additional region of the 23S rRNA detected both of these variants. A retrospective study of >18 million AC2 results tested between 2018-2019 did not display a decrease in CT positivity. CONCLUSIONS Although we did not detect the Fl-nvCT variant among US specimens, we show evidence that the low occurrence of similar diagnostic escape mutants can be detected with an updated AC2 assay using multiple 23S rRNA targets.