Abstract Body

The HIV-1 epidemic amongst men having sex with men (MSM) in the Netherlands is mainly driven by subtype B. Non-B subtypes are found mostly amongst heterosexuals immigrants from Sub-Saharan Africa. Therefore considering a phylogenetic tree of non-B polymerase sequences allows identifying the introductions into the MSM population in the Netherlands. This can be used to estimate the proportion of introductions that actually resulted in onward transmission and assess whether this differs between subtypes.

The ATHENA observational cohort includes anonymized patient data of virtually all patients with HIV in care in the Netherlands. Polymerase sequences were available for 39% (8978) of patients in November 2014. Maximum likelihood trees were built by subtype in MEGA with 500 bootstraps, under a General Time Reversible model and five gamma distributed categories. We considered clusters with bootstrap values ≥70% including ≥2 MSM (indicating onward transmission), and those including ≥3 MSM (as indicative of ongoing established transmission clusters). The remaining MSM sequences were regarded as separate introductions, although some sequences formed clusters that were not statistically supported. The mean outbreak size per subtype was calculated as the number of sequences from MSM divided by the number of introductions amongst MSM.

In ATHENA, 2131 of patients diagnosed between 1981-2014 with an HIV-1 non-B infection have a sequence available. Of these, 1467 self-reported being infected through heterosexual and 337 through MSM contact. Of the heterosexuals, 71% (1037) originated from Sub Saharan Africa, and 18% (262) from the Netherlands; of the MSM 8% (26) originated from Sub Saharan Africa and 66% (222) from the Netherlands. We built separate trees for subtypes A, CRF01AE, CRF02AG,C,D,F,G.  The main results are summarized in table 1. The largest tree of 636 subtype CRF02AG sequences also contained most sequences from MSM. The proportion of successful introductions was highest for subtype F, the tree had the highest proportion of sequences from MSM, and was found to have the largest average outbreak size. Interestingly the median viral load at first hospital visit was significantly higher for MSM infected with subtype F compared to the MSM infected with other non-B subtypes.

Non-B subtypes are being introduced into the MSM population in the Netherlands and have gone on to form national sub-epidemics with different mean outbreak sizes.