Background: The CHAVI002 study was designed to characterize immune responses, particularly HIV-specific T-cell
responses, amongst 2 cohorts of HIV-exposed seronegative (HESN) individuals. The absence of a clear definition of HESNs
has impaired comparison of research within and between such cohorts. This report describes two distinct HESN cohorts and
attempts to quantify HIV exposure using a ‘HIV risk index’ (RI) model.
Methods: HIV serodiscordant couples (UK; 24, Uganda; 72) and HIV unexposed seronegative (HUSN) controls (UK; 14,
Uganda; 26 couples, 3 individuals) completed sexual behavior questionnaires every 3 months over a 9 month period. The
two cohorts were heterogeneous, with most HESNs in the UK men who have sex with men (MSM), while all HESNs in
Uganda were in heterosexual relationships. Concordance of responses between partners was determined. Each participant’s
sexual behavior score (SBS) was estimated based on the number and type of unprotected sex acts carried out in defined
time periods. Independent HIV acquisition risk factors (partner plasma viral load, STIs, male circumcision, pregnancy) were
integrated with the SBS, generating a RI for each HESN.
Results: 96 HIV serodiscordant couples completed 929 SBQs. SBSs remained relatively stable amongst the UK cohort, whilst
decreasing from Visit 1 to 2 in the Ugandan cohort. Compared to the Ugandan cohort, SBSs and RIs in the UK cohort were
lower at visit 1, and generally higher at later visits. Differences between the cohorts, with lower rates of ART use in Uganda
and higher risk per-act sex in the UK, had major impacts on the SBSs and RIs of each cohort. There was one HIV transmission
event in the UK cohort.
Conclusions: Employment of a risk quantification model facilitated quantification and comparison of HIV acquisition risk
across two disparate HIV serodiscordant couple cohorts.