The diagnostic-escape Finnish new variant of Chlamydia trachomatis first described in 2019 remains present in Finland three years after the introduction of an updated Aptima Combo 2 assay

In 2019, a new variant of Chlamydia trachomatis (Finnish new variant, FI-nvCT) that escaped detection by the widely used nucleic acid amplification test (NAAT) Aptima Combo 2 (AC2; Hologic Inc., San Diego, CA, USA) was detected in Finland [ [1] Rantakokko-Jalava K. Hokynar K. Hieta N. Keskitalo A. Jokela P. Muotiala A. et al. Chlamydia trachomatis samples testing falsely negative in the Aptima Combo 2 test in Finland. Euro Surveill. 2019; 241900298https://doi.org/10.2807/1560-7917.ES.2019.24.22.1900298 Crossref PubMed Scopus (22) Google Scholar , [2] Hokynar K. Rantakokko-Jalava K. Hakanen A. Havana M. Mannonen L. Jokela P. et al. The Finnish new variant of Chlamydia trachomatis with a single nucleotide polymorphism in the 23S rRNA target escapes detection by the Aptima Combo 2 test. Microorganisms. 2019; 7: 227https://doi.org/10.3390/microorganisms7080227 Crossref PubMed Scopus (14) Google Scholar ] and subsequently in other Nordic countries [ [3] Unemo M. Hansen M. Hadad R. Puolakkainen M. Westh H. Rantakokko-Jalava K. et al. Sensitivity, specificity, inclusivity and exclusivity of the updated Aptima Combo 2 assay, which provides detection coverage of the new diagnostic-escape Chlamydia trachomatis variants. BMC Infect Dis. 2020; 20: 419https://doi.org/10.1186/s12879-020-05148-7 Crossref PubMed Scopus (8) Google Scholar ]. The FI-nvCT yielded only slightly elevated relative light units (RLUs) in the AC2 assay, and the test results were interpreted as negative or equivocal [ 1 Rantakokko-Jalava K. Hokynar K. Hieta N. Keskitalo A. Jokela P. Muotiala A. et al. Chlamydia trachomatis samples testing falsely negative in the Aptima Combo 2 test in Finland. Euro Surveill. 2019; 241900298https://doi.org/10.2807/1560-7917.ES.2019.24.22.1900298 Crossref PubMed Scopus (22) Google Scholar , 2 Hokynar K. Rantakokko-Jalava K. Hakanen A. Havana M. Mannonen L. Jokela P. et al. The Finnish new variant of Chlamydia trachomatis with a single nucleotide polymorphism in the 23S rRNA target escapes detection by the Aptima Combo 2 test. Microorganisms. 2019; 7: 227https://doi.org/10.3390/microorganisms7080227 Crossref PubMed Scopus (14) Google Scholar , 3 Unemo M. Hansen M. Hadad R. Puolakkainen M. Westh H. Rantakokko-Jalava K. et al. Sensitivity, specificity, inclusivity and exclusivity of the updated Aptima Combo 2 assay, which provides detection coverage of the new diagnostic-escape Chlamydia trachomatis variants. BMC Infect Dis. 2020; 20: 419https://doi.org/10.1186/s12879-020-05148-7 Crossref PubMed Scopus (8) Google Scholar ]. The FI-nvCT has a single nucleotide polymorphism (SNP) in the 23S rRNA gene (C1515T) [ [2] Hokynar K. Rantakokko-Jalava K. Hakanen A. Havana M. Mannonen L. Jokela P. et al. The Finnish new variant of Chlamydia trachomatis with a single nucleotide polymorphism in the 23S rRNA target escapes detection by the Aptima Combo 2 test. Microorganisms. 2019; 7: 227https://doi.org/10.3390/microorganisms7080227 Crossref PubMed Scopus (14) Google Scholar ], and this SNP was shown to be the root cause of AC2 false negative/equivocal C. trachomatis specimens. Promptly after the discovery of the FI-nvCT, the manufacturer offered reflex testing of specimens with low C. trachomatis RLU values (≥15–99) with the Aptima C. trachomatis assay, which targets the C. trachomatis 16S rRNA sequence. After appropriate validation, an updated U.S. Food and Drug Administration–approved AC2 assay with two C. trachomatis 23S rRNA target sequences designed to detect the newly described AC2 diagnostic-escape nvCTs was made available internationally in 2020 [ [3] Unemo M. Hansen M. Hadad R. Puolakkainen M. Westh H. Rantakokko-Jalava K. et al. Sensitivity, specificity, inclusivity and exclusivity of the updated Aptima Combo 2 assay, which provides detection coverage of the new diagnostic-escape Chlamydia trachomatis variants. BMC Infect Dis. 2020; 20: 419https://doi.org/10.1186/s12879-020-05148-7 Crossref PubMed Scopus (8) Google Scholar ]. The aim of the present study was to investigate the occurrence of the FI-nvCT and other previously described AC2 diagnostic-escape nvCTs in Finland in 2022, i.e., 3 years after the introduction of the updated AC2 assay.