Evaluating GeneXpert point-of-care testing for STIs

GeneXpert point-of-care (POC) testing can detect chlamydia (CT), gonorrhoea (NG) and trichomonas (TV), according to a recent study published in BMC Infectious Diseases.

Sexually transmitted infections (STIs) remain a major global health concern, with 374 million new STI cases globally in 2020 caused by Ct, NG, and TV. Untreated infections in women may lead to pelvic inflammatory diseases, human immunodeficiency virus (HIV), low birth weight, neonatal death, stillbirth, and prematurity and congenital abnormalities.

STIs don’t often present with symptoms, and symptoms that do appear are often non-specific. Syndromic management is employed as first line treatment by low- and middle-income countries, which can cause a missed diagnosis or overtreatment. POC testing (POCT) can allow molecular testing for STIs, but concerns have arisen over clinical performance.

Investigators conducted a study to evaluate the efficacy of GeneXpert POCT for detecting CT, NG, and TV. Participants included women aged 18 years or older considered at risk of STIs. Women were considered at risk if they had unprotected sexual intercourse in the past 12 months, prior STI, performed sex work, or lived in remote Aboriginal communities.

Demographic, PCOT, clinical examination, and STI history data was obtained through interviews with a clinic nurse. Two vaginal swab samples were also obtained for each participant, one using a Cepheid Xpert specimen collection kit (Cepheid, Sunnydale, California, USA) and the other using a collection transport media.

CT, NG, and TV testing were performed using the GeneXpert system (Cepheid, Sunnydale, California, USA). The automated, cartridge-based system detects CT through a single gene target and NG through 2 gene targets. TV was detected qualitatively using separate gene cartridges, with 1 gene target.

POC test results included positive, negative, invalid, error, and no result. Information was recorded in the World Health Organization clinical trial management system by a designed data entry operator.

There were 1383 women included in the analysis, 58.6% from South Africa, 29.2% from Morocco, 6.2% from Guatemala, and 6% from Australia. Of participants, 48.9% were aged 20 to 24 years, 13% 18 to 19 years, 8% 25 to 29 years, 7% 30 to 34 years, 6% 35 to 39 years, 8% 40 to 44 years, 4% 45 to 49 years, and 6% from 50 to 69 years.

Approximately 70% of patients indicated they would be willing to wait at the clinic directly after undergoing testing to receive the test results. Approximately 39% indicated they would be willing to wait up to 20 minutes, 28% up to 30 minutes, 13% up to an hour, 12% up to 2 hours, and 7% other times or unsure.

Prior NG was reported in 4.2% of patients, CT in 1.7%, HIV in 20.8%, syphilis in 6.8%, TV in 4.4%, and other STI symptoms in 50%. Administration of any antibiotic in the past 3 weeks was reported by 8.9% of participants.

There were 1296 samples obtained for CT and NG and 1380 obtained for TV. Of CT tests, 24 were unsuccessful from the GeneXpert vs 16 from the reference laboratory. For NG, these numbers were 19 and 22, respectively, and 13 and 22, respectively for TV. In comparison, there were 1255 valid CT tests, 1256 valid NG tests, and 1345 valid TV tests.

The specificity of the GeneXpert system was 97% or higher for CT, 98% or higher for NG, and 98% or higher for TV. Sensitivity rates were 83.7%, 90.5%, and 64.7%, respectively.

These results indicated efficacy from the GeneXpert system in detecting CT, NG, and TV. However, negative likelihood ratios had decreased quality than expected, especially for TV.

Reference

Shephard, M., Matthews, S., Kularatne, R. et al. Independent clinic-based evaluation of point-of-care testing for the screening of Chlamydia trachomatis, Neisseria gonorrhoea and Trichomonas vaginalis in women-at-risk in Australia, Guatemala, Morocco, and South Africa. BMC Infect Dis. 2024;24(1). doi:10.1186/s12879-024-09018-4