Background Estimating STI prevalence and incidence are important for programming and advocacy. Current global and regional estimates are based on meta-analysis of prevalence data of gonorrhoea, chlamydia and trichomoniasis among low-risk populations, and on national surveillance of syphilis sero-prevalence among antenatal care attendees, with adjustment for laboratory test types, geography and age. The precision and utility of these estimates is limited by insufficient, varying, and uncertain data availability and quality, notably on duration of infection and symptoms, representativeness of survey samples, etc. Current estimation methods are not able to incorporate data from high risk populations and are not able to generate national STI estimates.

The Spectrum suite of estimation and program planning tools has been developed to support estimation of burdens, trends, service needs and program impact for family planning, HIV/AIDS, tuberculosis and other diseases. The HIV/AIDS, Spectrum is used by over 120 countries every two years to estimate their burden of HIV/AIDS, antiretroviral treatment need and other services.

Next generation of estimating STIs A module for estimating burdens and trends of STIs in the Spectrum suite of health modelling tools is being developed, initially for gonorrhoea and syphilis, for which relatively good and abundant country data are available. The Spectrum module will fit STI burdens and trends using standard STI indicators collected routinely by countries and reported annually to the WHO and UNAIDS through the Global AIDS Response Progress Reporting (GARPR) system and STI data on general populations from peer-reviewed literature.

By building onto the HIV/AIDS model within Spectrum, the STI estimation tool will benefit from efficiency, expertise, coherence and consistency with estimations of HIV/AIDS.

Next steps The development and piloting of the Spectrum STI module is a first phase towards supporting country-level STI estimation and program planning. The STI module will be implemented in selected countries in. two-yearly cycle of country consultations tagged into the UNAIDS HIV/AIDS estimation. A companion module for strategic STI intervention modelling, program planning and costing – as an extension to Spectrum’s current One Health Tool representation of MNCH, family planning and HIV primary/behavioural prevention programs will be designed and developed.