Can network-based testing services have an impact beyond testing for HIV?

HIV, hepatitis B and hepatitis C cause an estimated 4.3 million new infections and 1.74 million deaths per year; sexually transmitted infections (STIs) affect 1 million people daily.^1–4 Global targets call for 95% of people with HIV to be diagnosed, on treatment, and virally suppressed; a 90% reduction in new viral hepatitis infections; and a 90% reduction of syphilis and gonorrhoea, in addition to the elimination of mother-to-child transmission of HIV, hepatitis B and syphilis. Integrating service delivery is crucial for achieving these goals.

Network-based testing (NBT) services, including social network testing, partner services, and family and household testing modalities, encompass services that may include contacting, notifying, testing, and/or treating partners, social contacts, household members and family members of those with STIs or blood-borne infections. These essential testing strategies can expand access beyond diagnosed individuals to include social and geographic risk networks. Although effective for HIV,^5–7 many questions remain about delivering integrated services while respecting client choice and confidentiality.⁸ Direct evidence for partner services for other STIs or hepatitis B and C is limited, as well as evidence on using partner services to deliver prevention interventions, or integrating services across HIV/STIs and hepatitis B and C.

Although NBT modalities have been used to identify, notify, test and/or treat partners of individuals with STIs for decades,⁹ the World Health Organization recommended HIV partner services in 2016 and social network testing in 2019.¹⁰ These services have shown success in various settings, with HIV yield among partners reached through partner services generally ranging from 12% to 86%,¹¹ depending on context and programming, whereas the yield for most testing programs has fallen below 5% globally.¹² Approaches using immediate provider-assistance appear to improve linkage to care and can encourage re-engagement compared with other passive partner referral approaches.^13,14 Although ethical and safety concerns may exist, particularly when these services are driven by yield targets or conducted without consent,¹⁵ studies have yet to find significant increases in harm, interpersonal violence or other adverse events.¹⁶

Recent innovations have expanded the ways in which NBT can be delivered, using phone calls,¹⁷ virtual notification platforms,¹⁸ community and peer-led implementation^14,19 enhanced social support²⁰ and self-testing.²¹ Although effective for case finding and engaging partners in care, optimal service delivery practices for different populations and settings need further documentation.

Social network testing services (SNS) encourage individuals to motivate those in their social and geographic networks who may benefit from HIV testing to test for HIV through offering information about testing services or distributing self-tests. SNS can increase uptake of HIV testing – through HIV self-testing or standard testing – among sexual partners and social contacts of test promoters.²² Social network approaches may also increase the number of first-time testers. Although SNS are increasingly used for HIV, adoption for viral hepatitis or other STIs remains limited.

Research gaps exist in NBT implementation and outcomes for HIV, hepatitis B and C, and other STIs (Fig. 1). The effectiveness of partner services for identifying, notifying, testing, treating and/or linking to care partners who have been exposed to STIs other than HIV is scarce, despite decades of experience with this practice as standard of care. Although provider-assisted partner services positively impact linkage to care for partners,²³ further research is needed to evaluate provider-assisted models for delivering partner services for other STIs.⁸ Expedited partner therapy can treat sexual partners and reduce reinfections for some bacterial STIs, and is especially important for pregnant women.²⁴ However, feasibility, costs and risks of contributing to drug resistance have to be weighed. Considering the existence of different pathogens, and the variable accessibility of testing and treatment, significant challenges exist to consolidating evidence or developing global guidance for STI NBT beyond HIV.

Fig. 1.

Network-based testing services implementation questions: the who, what, when, where, how and how much.

Direct evidence on the effectiveness of partner services for hepatitis B and C is also scant. Although some early studies among people who inject drugs showed low effectiveness of partner services for those with chronic hepatitis B and C,^25,26 more recent evidence using different approaches, including peer-educator delivered strategies, have had more success,²⁷ and there is increasing advocacy to use NBT services as a tool in global viral hepatitis control.²⁸

Leveraging partner services for cross-cutting goals in HIV, other STIs and viral hepatitis is promising. Recent research suggests that providing services for partners of people who inject drugs living with HIV can achieve high rates of case-finding for hepatitis C,^14,27 and that partner services for partners of people with some STIs can result in high yield for HIV testing.²⁹ Testing for both HIV and syphilis using dual rapid diagnostic tests is increasingly being used in antenatal clinics.³⁰ Given the need to diagnose partners to prevent incident infections and reinfections during pregnancy, the use of dual testing among partners of pregnant people may also be effective.^31,32 Dual testing is also suggested by the WHO for use in key populations and their partners.³³ Furthermore, hepatitis B testing may be appropriate for partners and household contacts of certain priority populations, including pregnant women, people who inject drugs, and gay men and other men who have sex with men.³⁴ Multiplex testing with rapid testing for two or more pathogens in one test is becoming increasingly possible, with specific test platforms being defined for different populations.^35,36 More research is needed to define optimal packages of partner testing and care for different populations in different settings and for different pathogens and test kits.

Self-testing is a promising self-care modality for delivering partner services.³⁷ Although global adoption of HIV self-testing since the WHO recommended it in 2016¹⁰ has been rapid, opportunities to scale-up are still needed. To date, secondary HIV self-testing distribution has largely been used to reach men through distribution by women in antenatal care clinics.³⁸ It has also been integrated within SNS strategies.³⁹ However, despite potentially high yield, HIV self-testing distribution has not yet been fully integrated into the standard package of partner services options.

In 2021, the WHO recommended self-testing for hepatitis C, raising the possibility of secondary distribution of self-testing for hepatitis C kits to sexual and injection partners or social contacts of people with HCV.⁴⁰ However, studies demonstrating effectiveness of this practice are lacking. Self-testing for syphilis is in the pipeline as well,⁴¹ presenting the opportunity for partner self-testing. Increasingly, dual and multiplex testing for different conditions, including gonorrhoea and chlamydia, are in development, and could be used for secondary distribution to partners. Self-collection of samples is another strategy to reach sexual partners and to implement secondary distribution within social networks.⁴²

Finally, evidence to support the use of partner services in linking to or delivering combination prevention is lacking. Given the high prevalence of HIV, STIs, and/or viral hepatitis found in different key and priority populations,³³ many partners contacted could likely benefit from the offer of or information about pre-exposure or post-exposure prophylaxis for HIV, hepatitis B vaccination, condom promotion and/or other prevention methods.²⁰ Doxycycline as post-exposure prophylaxis for some bacterial STIs is being considered for gay men and other men who have sex with men and transgender women in some settings,⁴² but its feasibility, impact and cost-effectiveness in other settings is uncertain. Once indications for doxycycline as post-exposure prophylaxis are better defined, this could also be considered in a package of services for some partners.

Partner services may not be effective or appropriate for all populations or in all settings. In Zimbabwe, passive partner referral for adolescent girls and young women was not successful, with only 5.7% uptake of partner treatment.⁴³ It was noted in this context that index disclosure to partners may have the potential for social harms, particularly with casual partners and in age-disparate sexual relationships; however, provider-assisted partner services or SNS approaches were not offered.^43,44 Similarly, there may be challenges for people from some key populations, particularly when identifying or notifying partners engaging in criminalised and/or stigmatised activities. It is therefore important to further evaluate barriers to NBT services for different populations, and identify potential strategies to provide partners and social contacts with access to testing options. SNS may be more appropriate for young people and people from some key populations, but evidence comparing SNS and provider-assisted options is lacking.

Finding sexual and injecting partners or other contacts of people with HIV, other STIs, or hepatitis B and C can be resource-intensive, but the provision of NBT offers many integration opportunities across disease areas.⁴⁵ Healthcare worker training and support for delivering NBT services are essential.⁴⁶ Further research on service delivery to engage, notify, test, treat, and link to care partners and contacts of individuals diagnosed with these infections is needed. Multiplex testing and self-testing within NBT services should be further assessed for feasibility and effectiveness, including linkage to treatment and prevention. New strategies are necessary to address the syndemics of HIV, viral hepatitis and STIs, which are prevalent and inadequately addressed in many populations. Integrating care and delivery, including for NBT services, could improve health system efficiency, but requires further research to guide implementation. Evidence can then inform the definition of integrated packages of interventions for partners and other contacts.