Sexually Transmitted Infections

Molecular diagnosis of STIs

• Results should be interpreted together with symptoms, sexual history, clinical findings, sample type and other diagnostic procedures.

• A positive result indicates detection of the corresponding target in the sample, but does not by itself define clinical severity, microorganism viability, infectiousness or antimicrobial susceptibility.

• A negative result does not exclude infection if the pathogen load is low, sample quality is suboptimal, the anatomical site sampled is not appropriate, amplification inhibitors are present or the causative agent is not included in the assay.

• Co-infections may be detected. Each positive result should be interpreted according to the clinical syndrome and the microorganism identified.

• For Neisseria gonorrhoeae, molecular detection does not provide information on antimicrobial susceptibility. Culture and susceptibility testing may be required in cases of suspected treatment failure or for resistance surveillance.

• In the context of genital ulcer disease, detection of HSV-1, HSV-2, VZV, CT-LGV, T. pallidum, H. ducreyi or MPXV should be interpreted according to lesion type, anatomical location, time since onset and epidemiological context.

• Detection of Mycoplasma genitalium is particularly relevant in persistent or recurrent urethritis, cervicitis or selected cases of pelvic inflammatory disease. Resistance testing should be considered when available.

• Genital ulcer syndromes cannot be reliably diagnosed based on clinical appearance alone. Molecular detection in lesion samples supports etiological diagnosis, but should be interpreted together with lesion stage and epidemiological context.

• A positive molecular result for Treponema pallidum supports detection in the lesion sample, but syphilis serology remains necessary for staging, follow-up and clinical management.

• When mpox is suspected, material obtained from skin lesions is the preferred specimen type for molecular confirmation.

• Mycoplasma hominis and Ureaplasma spp. may be part of the urogenital microbiota. Their isolated detection does not confirm disease and should not be used as the sole criterion for treatment decisions.

• Detection of CT-LGV, T. pallidum, N. gonorrhoeae or MPXV may require specific clinical or public health actions according to local guidelines.

• Detection of C. trachomatis serovar L / LGV should be interpreted according to sample type, clinical presentation and epidemiological risk factors, especially in rectal infections or workflows related to ulcerative lesions.

• Invalid or inconclusive results should be repeated, preferably after re-extraction of nucleic acid from the original sample. If poor sample quality or inhibition is suspected, a new sample should be considered.

Sources

• Workowski KA, Bachmann LH, Chan PA, Johnston CM, Muzny CA, Park I, et al. Sexually transmitted infections treatment guidelines, 2021. MMWR Recomm Rep. 2021;70(4):1-187. https://doi.org/10.15585/mmwr.rr7004a1

• Jensen JS, Cusini M, Gomberg M, Moi H. 2021 European guideline on the management of Mycoplasma genitalium infections. J Eur Acad Dermatol Venereol. 2022;36(5):641-650. https://doi.org/10.1111/jdv.17972

• Horner P, Donders G, Cusini M, Gomberg M, Jensen JS, Unemo M. Should we be testing for urogenital Mycoplasma hominis, Ureaplasma parvum and Ureaplasma urealyticum in men and women? A position statement from the European STI Guidelines Editorial Board. J Eur Acad Dermatol Venereol. 2018;32(11):1845-1851. https://doi.org/10.1111/jdv.15146

• World Health Organization. Diagnostic testing and testing strategies for mpox: interim guidance. Geneva: WHO; 2024. Available from: https://www.who.int/publications/i/item/WHO-MPX-Laboratory-2024.1