Slovenia is a small Central European country with a relatively modest burden of HIV disease, with fewer than 1 per 1,000 inhabitants infected. The HIV epidemic mostly affects men who have sex with men (MSM), with subtype B as the most represented subtype in over 85% of patients. The aim of this study was to establish the properties of the subtype B HIV epidemic in Slovenia up to the end of 2012.
For the purpose of this study, data and sequences were gathered from 3 previous studies conducted in Slovenia examining the prevalence of transmitted drug resistance among therapy naïve HIV-1 positive patients diagnosed in the years 2000-2012. Only subtype B sequences were selected for this study (determined by the REGA HIV-1 Subtyping tool, v2.0), a total of 223 partial pol gene sequences were included, representing 52% of all patients newly diagnosed in 13 years.
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The maximum likelihood (ML) phylogenetic tree was constructed using PhyML 3.0 and transmission clusters were identified according to the approximate likelihood ratio test branch support values (>0.90). The Monte Carlo Markov chain method available in the BEAST package v1.7.1 was employed, using a relaxed clock model with uncorrelated lognormal distribution and the Bayesian skyline coalescent model. The clusters previously identified in the ML analysis were reviewed and confirmed according to posterior probability values (>0.990).
Combined analysis (ML and Bayesian analysis) revealed 8 major clusters (n≥10 patients), 1 group of 4 patients, 2 trios and 12 transmission pairs. Among 223 included individuals, 146 (65.5%) patients belonged to large transmission clusters comprising 10 or more individuals and 34 (15.2%) patients to small clusters of 2-4 patients, leaving only 43 (19.3%) of the Slovenian patients infected with subtype B without an epidemiological link observed by phylogenetic inference. Statistical analysis examining the characteristics of patients found in large clusters revealed significantly fewer patients in a cluster diagnosed prior to 2005 (p=0.0388) and significantly more patients reported Slovenia as the country in which the infection occurred (p<0.0001) compared to other countries.
In conclusion, several introductions of HIV subtype B occurred in Slovenia. The majority of patients were found with a transmission link, exhibiting a closed HIV community, with the virus being transmitted predominantly between individuals within Slovenia.
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