Identifying youth at high risk for sexually transmitted infections in community-based settings using a risk prediction tool: a validation study

Abstract

Background Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are the most common bacterial sexually transmitted infections (STIs) worldwide. In the absence of affordable point-of-care STI tests, WHO recommends STI testing based on risk factors. This study aimed to develop a prediction tool with a sensitivity of > 90% and efficiency (defined as the percentage of individuals that are eligible for diagnostic testing) of < 60%. Methods This study offered CT/NG testing as part of a cluster-randomised trial of community-based delivery of sexual and reproductive health services to youth aged 16–24 years in Zimbabwe. All individuals accepting STI testing completed an STI risk factor questionnaire. The outcome was positivity for either CT or NG. Backwards-stepwise logistic regression was performed with p ≥ 0.05 as criteria for exclusion. Coefficients of variables included in the final multivariable model were multiplied by 10 to generate weights for a STI risk prediction tool. A maximum likelihood Receiver Operating Characteristics (ROC) model was fitted, with the continuous variable score divided into 15 categories of equal size. Sensitivity, efficiency and number needed to screen were calculated for different cut-points. Results From 3 December 2019 to 5 February 2020, 1007 individuals opted for STI testing, of whom 1003 (99.6%) completed the questionnaire. CT/NG prevalence was 17.5% (95% CI 15.1, 19.8) (n = 175). CT/NG positivity was independently associated with being female, number of lifetime sexual partners, relationship status, HIV status, self-assessed STI risk and past or current pregnancy. The STI risk prediction score including those variables ranged from 2 to 46 with an area under the ROC curve of 0.72 (95% CI 0.68, 0.76). Two cut-points were chosen: (i) 23 for optimised sensitivity (75.9%) and specificity (59.3%) and (ii) 19 to maximise sensitivity (82.4%) while keeping efficiency at < 60% (59.4%). Conclusions The high prevalence of STIs among youth, even in those with no or one reported risk factor, may preclude the use of risk prediction tools for selective STI testing. At a cut-point of 19 one in six young people with STIs would be missed.

Facilitators and barriers to point-of-care testing for sexually transmitted infections in low- and middle-income countries: a scoping review

“…However, a risk prediction tool may be inappropriate if prevalence is high even amongst individuals without risk factors. For example, non-selective testing was felt to be more appropriate for young people in Zimbabwe by Kranzer et al, as risk prediction tools developed were insufficiently sensitive for CT/NG [ 116 ].…”

Investigating point-of-care diagnostics for sexually transmitted infections and antimicrobial resistance in antenatal care in Zimbabwe (IPSAZ): protocol for a mixed-methods study

“…A prevalence of curable STIs between 32.0% and 37.0% has been reported in South Africa and Zambia 12–16. Our recent studies among female youth in Harare have demonstrated combined CT/NG prevalence between 18.2% and 19.5% 18 19. The prevalence of hepatitis B in pregnant women in South Africa has ranged between 3.1% and 5.3% 20–22.…”

“…A 2010 study found a TV prevalence of 11.8% and syphilis prevalence of 1.2% among pregnant women in Harare 17. Recent studies among female youth in Harare have demonstrated a combined CT/NG prevalence between 18.2% and 19.5% 18 19. A prevalence of hepatitis B ranging between 3.1% and 5.3% has been reported in pregnant women in South Africa 20–22…”

Derivation and Internal Validation of a Risk Score for Predicting Chlamydia trachomatis Infection in Kenyan Women Planning Conception

“…In another risk score developed in 15- to 29-year-old women in the Netherlands, predictors included age, area of residence, ethnicity, education status, urogenital symptoms, condom use, and number of sexual partners 30 . Other risk scores have combined multiple STIs as a single outcome 13–18 . 31s Prediction criteria included in these studies encompassed characteristics including age, sex, education, relationship status, number of sexual partners, HIV status, past pregnancy, perceived STI risk, new sexual partner, condom use, STI history, genital symptoms, and clinical signs of cervicitis.…”

“…In Africa, risk scores for CT have been developed for young adults, men who have sex with men, pregnant women, high-risk groups, women with HIV, and symptomatic women. [13][14][15][16][17][18][19] The present study aimed to assess the prevalence and correlates of chlamydial infections among Kenyan women planning to become pregnant and to develop and internally validate a risk score that could be used to identify women for secondary screening using NAATs.…”