Objectives To assess (i) the public health benefit of provider-led partner notification (PN) and (ii) the importance of taking into account the number and types of partners when assessing the cost-benefit of provider-led PN.

Method We used data on 346 partners reported by 220 chlamydia index patients (n=127 men) seen by a PN professional at one GUM clinic, April–June 2011. We used a published, evidence-based algorithm to quantify PN impact, including the measure the “Number Needed to Treat to Interrupt Transmission” (NNTIT), defined as the number of partners who need to be treated to interrupt 1 onward (secondary) transmission. A lower NNTIT indicates less PN effort is required to prevent onward transmission.

Results Men reported 216/346 partners and women 130/346. Men more often described partners as casual (56% vs 28%), while women more often reported regular (40% vs 30%) and ex-partners (23% vs 12%). For traceable partners (73% of men's; 88% of women's), 9/157 men's partners and 16/114 women's partners required provider-led PN. Almost all were casual or ex-partners (8/9 men's; 13/16 women's). NNTITs were lowest for ex-partners: 0.6 and 0.45 for men and women, respectively, followed by casual partners: 0.8 and 0.6, then regular partners: 1.80 and 0.9.

Discussion Provider-led PN is required more often with casual and ex-partners than with regular partners. This may have greater cost implications for services, but, as casual and ex-partners are likely to have greater numbers of partners themselves, the potential for preventing onward transmission is greater, yielding greater public health benefit. Services should collect data from their index patients on the number and type(s) of partners, as well as the PN method(s) required (patient vs provider referral). Together with cost data, these data were key for demonstrating the cost-benefit of provider-led PN.