Network-based strategies to combat HCV: Examining social and spatial drivers of transmission among PWID in New Delhi.

People who inject drugs (PWID) account for some of the fastest-growing HCV epidemics globally. While individual risk factors for infection are understood, less is known about network and spatial factors critical for elimination strategies. Two thousand five hundred twelve PWID in New Delhi, India, were recruited (2017-19) through network referrals. Biometrics identified duplicates and cross-network linkages. Participants completed semi-annual surveys and blood tests for HCV antibodies and RNA. Poisson regression and network analyses identified predictors of incident HCV and compared network-based intervention approaches. Baseline HCV antibody prevalence was 65.1%, of whom 79.6% were HCV RNA-positive. We observed 92 HCV seroconversions over 382.25 person-years (incidence: 24.1 per 100 person-years). Of the 92 seroconverters, 67% (62) were directly connected to an RNA-positive participant, and all were within one degree of separation from an RNA-positive participant. Individual-level factors associated with seroconversion included age, sexual activity, and injection behaviours. After adjusting for individual-level factors, seroconversion was significantly associated with number of RNA-positive partners (adjusted incidence rate ratio [AIRR] = 1.30) and injecting at a particular venue (AIRR = 2.53). This association extended to indirect ties, with 17% reduced odds of seroconversion for each degree of separation from the venue (AIRR = 0.83). Network analyses comparing intervention strategies found that targeting venues identified more cases compared to a treat-a-friend approach. We observed a fast-growing HCV epidemic driven by viremia within individuals' immediate networks and indirect social and spatial ties, demonstrating the importance of achieving broad, sustained virologic response and rethinking network-based interventions to include venues.