Many countries in sub-Saharan Africa (SSA) are focused on reaching the Joint United Nations Programme on HIV/AIDS (UNAIDS)’s 95–95-95 strategy (UNAIDS, 2015) and responding to the United Nations Sustainable Development Goal (SDG) 3 (UN, 2023). A 2016–2017 national population-based household survey conducted in Tanzania showed that only 61.0% of people living with HIV in Tanzania knew their status, (TACAIDS, 2018). To address this gap, the Government of Tanzania (GOT) through the Ministry of Health (MOH), in collaboration with the U.S. President’s Emergency Plan for AIDS Relief (PEPFAR), prioritized more effective and targeted HIV case identification strategies, such as index testing, optimized facility based provider-initiated testing and counseling (PITC), HIV self-testing and focused community HIV testing services (HTS) targeting key and vulnerable populations (KVP) at high risk of HIV infection (NACP, 2017, 2019). KVP is defined as groups at increased risk of HIV transmission/acquisition, i.e. female sex workers (FSW), men who have sex with men (MSM), and people who inject drugs (PWID), or long distance track drivers, fisherfolks/fishing community and miners/mining community (NACP, 2017)

Reflecting on the HIV case identification strategies deployed after the Tanzania HIV Impact Survey 2016–2017 (TACAIDS, 2018), one potential modality to improve HTS and HIV case identification activities was index testing, a case finding modality that demonstrated great programmatic impact in identifying individuals with undiagnosed HIV infections across most sub-populations and age groups (Dalal et al., 2017; Kahabuka et al., 2017; Lyamuya et al., 2020; Mahachi et al., 2019; Sharma et al., 2018). Understanding that the challenges of reaching undiagnosed PLHIV increase as the identification gap decreases (Chamie et al., 2021), Tanzania considered social network strategies (SNS testing) for HTS as an additional modality to reach networks at high risk for HIV and to identify PLHIV who would otherwise not be diagnosed through routine HTS (McCree et al., 2013; PEPFAR, 2023; Stojanovski et al., 2021). In 2021, PEPFAR recommended SNS testing to enhance HIV case finding among networks of high-risk individuals (PEPFAR, 2021b), especially in countries with large gaps to reaching UNAIDS’ first 95. These findings are consistent with the World Health Organization (WHO) and Centers for Disease Control and Prevention’s (CDC) descriptions of SNS as a case finding strategy that improves identification of PLHIV who do not know their HIV status (CDC, 2023; WHO, 2019). Additionally, SNS testing promoted uptake of HIV self-testing as well as Pre-exposure Prophylaxis (PrEP) (Chamie et al., 2021; Kwan et al., 2023; Lee & Schafer, 2023; Sheira et al., 2022), which are integral parts of HTS and HIV prevention respectively. Tanzania’s MOH, in collaboration with PEPFAR and its implementing partners (IPs), started to implement and report SNS testing data from both communities and facilities starting in October 2021 (PEPFAR fiscal year 2022) (PEPFAR, 2021a).

SNS testing has been implemented globally and in SSA (Chamie et al., 2021; Farquhar et al., 2022; Lee & Schafer, 2023) primarily targeting networks of KVP identified above (Girault et al., 2015), (Denisiuk et al., 2023), (Sheira et al., 2022). SNS testing was also used to complement index testing, which is an established effective HIV case finding modality. PEPFAR described this hybrid of modalities as “blended” where HIV positive index clients were used as seeds, who were given HTS referral coupons to take to index contacts who would not be elicited or reached through routine index testing (PEPFAR, 2023). The elicitation of index contacts who, for different reasons, cannot be identified through index testing are elicited as social contacts by SNS testing. This approach provided index cases the freedom of participation and safety assurance for themselves and their partners (Grimsrud et al., 2023; PEPFAR, 2021a), including age-discordant sexual partnerships with increased HIV risk to the younger partner (Ritchwood et al., 2016), due to social-legal issues like incarceration for sex with minor age, it may be challenging for an older index case to identify younger partners as sexual contacts under index testing program, would rather list them anonymously as social contact under SNS testing.

This paper describes performance of SNS testing scale-up, its trend over time and factors associated with uptake of SNS in Tanzania from October 2021 to March 2023. Also, it highlights efforts by GOT led by MOH under PEPFAR’s to ensure scale-up of SNS testing with fidelity and its potential impact on the overall HIV case finding strategies towards reaching HIV epidemic control.

This analysis highlighted the potential role of SNS testing, which showed exponential growth in identifying previously undiagnosed individuals over six quarters. Though not fully implemented across community and facility sites, the contribution of HIV-positives from SNS testing increased more than five times between quarters October – December 2021 and January – March 2023. The positivity rate from SNS testing was >6%, higher than the average positivity rate from the overall HTS program in Tanzania (~4%)(NACP, 2019), implying effectiveness of this model.

Community SNS testing contribution is higher compared to facility most probably because the implementation started in the communities compared to facility. The facility implementation rolled-out in phased approach that started with high-volume facilities (hospitals), down to lower-volume facilities i.e., health centers and dispensaries, which is why uptake of SNS testing in hospitals equals community. More females reached by SNS testing compared to males correlates with the overall Tanzania HTS program performance. The higher positivity rate of >10% among women aged >35 years and men aged >45 years (>15%), is consistent with results seen with the index testing modality.

SNS testing has been shown to be integrated well with other HIV case finding modalities, particularly index testing and HIV self-testing, as well as DREAMS and PrEP (Denisiuk et al., 2023; Farquhar et al., 2022; Girault et al., 2015; Kwan et al., 2023). SNS testing was used to reach unelicited sexual partners from index testing as social contacts and showed effectiveness on diagnosing new HIV infections among Adolescent Girls and Young Women (AGYW) in facility settings (i.e., 1,512 HIV-positive females aged 15–24 years identified through SNS testing with the positivity rate of >3% - more than average yield for AGYW) (NACP, 2017). These findings have potential benefits and opportunities to reduce new HIV infections in this priority age group.

Although children were not the target population for SNS testing, they were part of elicited social networks at risk of HIV. A total of 20 children living with HIV (CLHIV) aged ≤15 years were identified through SNS testing from 241 pediatric social contacts tested. The observed high positivity rate of 8.3% for identified CLHIV is about four times higher than the average rate for this population in Tanzania (~2%) (NACP, 2019). These findings prompted review of the program and data to better understand and apply SNS testing for HIV case finding among pediatric and adolescents.

Lack of systems that can support reporting of SNS testing and SNS testing outputs by sub-population type are observed limitations of this modality. These should be considered in prospective reviews of standardized national data recording and reporting tools as they are essential components for SNS testing program oversight and impact measurement.

This analysis investigated SNS testing implementation in both communities and health facilities targeting KVP. Much of the published literature on SNS globally and in SSA has focused on Key Populations (Boyer et al., 2013; Farquhar et al., 2022; Girault et al., 2015; Kwan et al., 2023; Maina et al., 2018; McCree et al., 2013). The increased HIV identification as the model was scaled-up underscores the potential of this HIV case-finding approach in Tanzania. The findings from this analysis suggested that there are still potential opportunities to further scale-up SNS testing in both communities and facilities, providing a solid signal to inspire full SNS testing roll-out, and closer monitoring of the program impact.

SNS testing demonstrated its effectiveness in reaching high-risk individuals who would otherwise not been reached through existing HTS modalities in Tanzania. The program implementation coverage thus far indicated that there are still opportunities to scale up this modality in both community and facility settings. Nonetheless, closer tracking of facility implementation is needed to ensure fidelity to the SNS model due to the persistent lower positivity rate. For useful and impactful oversight of the program, HTS systems should be enabled to capture beneficiaries’ population type and cascade of SNS testing. As Tanzania heads toward HIV epidemic control, the integration of innovative case-finding modalities as this is crucial to enhance identification of the undiagnosed PLHIV, and back-up the existing effective strategies like index testing.