Objective To develop and validate a risk scoring tool for chlamydia infection to identify those who are at increased risk of chlamydia infection.
Methods We used demographic, sexual behaviour information and chlamydia positivity results from more than 45 000 individuals who attended Sydney Sexual Health Centre between 1998 and 2009. Participants were randomly allocated to either the development or internal validation dataset. Using logistic regression, we created a prediction model and weighted scoring system using the development dataset and calculated the OR of chlamydia positivity for participants in successively higher quintiles of score. The internal validation dataset was used to evaluate the performance characteristics of the model for five quintiles of risk scores including population attributable risk (PAR), sensitivity and specificity.
Results In the prediction model, inconsistent condom use, increased number of sexual partners in last 3 months, genital or anal symptoms and presenting to the clinic for sexually transmitted infections (STIs) screening or contact of an STI case were consistently associated with increased risk of chlamydia positivity in all groups. High scores (upper quintile) were significantly associated with increased risk of chlamydia infection. A cut-point score of 20 or higher distinguished a “increased risk” group with a sensitivity of 95%, 67% and 79% among heterosexual men, women and MSM, respectively.
Conclusion The scoring tool may be included as part of a health promotion and/or clinic website to prompt those who are at increased risk of chlamydia infection which may potentially lead to increased uptake and frequency of testing.
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