Background

HIV transmission risk during acute and early HIV infection (EHI) is sharply elevated, but the contribution of EHI to ongoing HIV transmission is controversial. However, in settings where EHI contributes substantially to secondary transmissions, early diagnosis and intervention may be critical for HIV prevention. We estimated the contribution of EHI to HIV incidence in Lilongwe, Malawi and predicted the future impact of hypothetical prevention interventions affecting EHI only, chronic HIV infection (CHI) only, or both stages.

Methods

We developed a deterministic mathematical model describing heterosexual HIV transmission, informed by detailed behavioural and viral load data collected in Lilongwe. We included sexual contact within and outside steady pairs and divided the infectious period into multiple intervals to allow for changes in transmissibility by infection stage. We used a Bayesian melding approach to fit the model to HIV prevalence data collected over time at Lilongwe antenatal clinics. We evaluated interventions that reduced the per-contact transmission probability to 0·00003 in those receiving them and varied the proportion of individuals receiving the intervention in each stage.

Findings

We estimated that 38·4% (95% credible interval: 18·6%-52·3%) of ongoing HIV transmissions in Lilongwe are attributable to sexual contact with EHI index cases. Interventions acting only during EHI substantially reduced HIV prevalence, but did not lead to elimination, even with 100% coverage. Interventions acting only during CHI also reduced HIV prevalence, but coverage levels of 95%-99% were required to move the epidemic toward elimination. In scenarios with <95% CHI coverage, additional interventions reaching 25%-75% of EHI cases reduced HIV prevalence substantially.

Interpretation

Our results suggest that EHI plays an important role in HIV transmission in this sub-Saharan African setting. Without near-perfect coverage, interventions during CHI will likely have incomplete effectiveness unless complemented by strategies targeting the heightened transmission risk of EHI.