Most HIV transmission occurs within households or within communities, even among highly mobile fishing communities around Lake Victoria

Editor’s notes: It is well recognized that the fishing communities around Lake Victoria have high HIV prevalence.  Fishermen move around to find the best yield and women who buy and sell fish often meet the boats at different fishing villages and may also trade sex for the best fish to maximize their business. It is therefore, perhaps, surprising that Kiwuwa-Muyingo and colleagues’ study of the phylogenetics of HIV in five distinct fishing communities in Uganda shows that 83% of the transmission events occur in the context of either household or the local community.  Transmission between the communities was less common than expected.  On the other hand, many isolates of HIV could not be linked to another isolate in the study, suggesting that they had been imported into the region, or that their transmission cluster had not been sampled.  A major challenge for molecular epidemiology studies is that limited coverage of the sampling means that unique isolates might have become linked isolates if the sampling had included more of the population.  The authors of this study estimate that they included approximately 44% of all HIV positive individuals in this study cohort, which is similar or better than many phylogenetic studies, but still leaves a lot of room for misclassification biases. A strength of the study was that the authors also included HIV isolates from individuals who had been HIV-negative and followed up over an 18-month period.  Among the 34 transmission clusters, 11 included at least one incident case.  Although the numbers become too small to be confident, they found that in 36% (4) of these 11 clusters, transmission was likely from one incident case to another incident case.  This is an important observation as it highlights the ongoing spread of HIV from recent infection. Transmission of this sort is harder to prevent through the scale up of treatment as it would require people to be tested very regularly, to start treatment before their partner was infected too.  Another interesting observation, again based on limited numbers, is that HIV subtype C was more likely to be involved in transmission clusters than subtype A, which in turn was more commonly in clusters than subtype D.  Subtype C is not so common and presumably imported into these communities, whereas subtypes A and D are the most common subtypes.  We are still in the early days of phylogenetics among African isolates of HIV and many studies have significant limitations, so interpretation needs to be cautious.  Nonetheless, these techniques will increasingly shed light on the complex and sometimes unexpected interactions between individuals, communities, occupations, migration and HIV subtypes.  These insights should help us to focus our HIV prevention and treatment efforts to maximize their impact in the future. 

HIV-1 transmission networks in high risk fishing communities on the shores of Lake Victoria in Uganda: A phylogenetic and epidemiological approach.

Kiwuwa-Muyingo S, Nazziwa J, Ssemwanga D, Ilmonen P, Njai H, Ndembi N, Parry C, Kitandwe PK, Gershim A, Mpendo J, Neilsen L, Seeley J, Seppälä H, Lyagoba F, Kamali A, Kaleebu P. PLoS One. 2017 Oct 12;12(10):e0185818. doi:10.1371/journal.pone.0185818. eCollection 2017.

Background: Fishing communities around Lake Victoria in sub-Saharan Africa have been characterised as a population at high risk of HIV-infection.

Methods: Using data from a cohort of HIV-positive individuals aged 13-49 years, enrolled from 5 fishing communities on Lake Victoria between 2009-2011, we sought to identify factors contributing to the epidemic and to understand the underlying structure of HIV transmission networks. Clinical and socio-demographic data were combined with HIV-1 phylogenetic analyses. HIV-1 gag-p24 and env-gp-41 sub-genomic fragments were amplified and sequenced from 283 HIV-1-infected participants. Phylogenetic clusters with ≥2 highly related sequences were defined as transmission clusters. Logistic regression models were used to determine factors associated with clustering.

Results: Altogether, 24% (n = 67/283) of HIV positive individuals with sequences fell within 34 phylogenetically distinct clusters in at least one gene region (either gag or env). Of these, 83% occurred either within households or within community; 8/34 (24%) occurred within household partnerships, and 20/34 (59%) within community. 7/12 couples (58%) within households clustered together. Individuals in clusters with potential recent transmission (11/34) were more likely to be younger 71% (15/21) versus 46% (21/46) in un-clustered individuals and had recently become resident in the community 67% (14/21) vs 48% (22/46). Four of 11 (36%) potential transmission clusters included incident-incident transmissions. Independently, clustering was less likely in HIV subtype D (adjusted Odds Ratio, aOR = 0.51 [95% CI 0.26-1.00]) than A and more likely in those living with an HIV-infected individual in the household (aOR = 6.30 [95% CI 3.40-11.68]).

Conclusions: A large proportion of HIV sexual transmissions occur within house-holds and within communities even in this key mobile population. The findings suggest localized HIV transmissions and hence a potential benefit for the test and treat approach even at a community level, coupled with intensified HIV counselling to identify early infections.

Abstract  Full-text [free] access


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