Mining for pairs: shared clinic visit dates identify steady HIV positive partnerships. HIV Medicine
Marzel et al. examined the hypothesis that some stable HIV-infected partnerships can be found in cohort studies, as the patients frequently attend the clinic visits together. Their method to identify steady transmission pairs and serosorting couples was based on the intuition that pairs of patients who share a larger number of visits than expected by chance are more likely to represent pairs who coordinate their visits to the clinics, which might reflect being either steady transmission pairs or serosorting couples. Transmission pairs were identified based on three validation criteria: (i) monophyletic clustering on the phylogenetic tree and a maximal genetic distance of 2.5% between sequences; (ii) a self-report of having an HIV-positive steady partner by both members of the pair; and (iii) belonging to the same HIV transmission risk group.
The authors analyzed 434’432 visits for 16’139 Swiss HIV Cohort Study patients from 1990 to 2014. For 89 pairs, the number of shared visits exceeded the number expected. Of these, thirty-three pairs (37%) were confirmed using all three criteria. Notably, 12 of the validated transmission pairs (36%) were of a mixed ethnicity with a large median age gap, harbouring HIV-1 of predominantly non-B subtypes, suggesting imported infections.
In conclusion, the study suggests that steady, mixed-ethnicity partnerships with a large age gap (with the man being white and older) contribute to heterosexually driven migration events. This observation opens up a targeted prevention opportunity. In addition, this simple method widens the horizons of research on within-pair quasi-species exchange, transmitted drug resistance and viral recombination at the biological level.