In cluster A, ZPHI-A1 and ZPHI-A2 formed a serodiscordant couple living in monogamous relationship. ZPHI-A2 has been infected 304 days after ZPHI-A1 stopped continuing early ART. Transmission occurred during the chronic phase of the index partner while his viral load was 33 478 copies/ml.
In cluster B, ZPHI-B2 has been infected most likely by passive anal intercourse during the chronic phase of ZPHI-B1 136 days after discontinuing early ART. The viral load at the estimated timepoint of infection was 930 copies/ml.
ZPHI-C1 and ZPHI-C2 together consulted our outpatient clinic because they suspected HIV infection of ZPHI-C2 due to symptoms of an acute retroviral syndrome. Actually, ZPHI-C1 infected ZPHI-C2 146 days after stopping ART (viral load 2237 copies/ml) during chronic phase. Because they formed a monogamous relationship at that time the two additional SHCS patients within this cluster could be excluded as potential transmitters to patient ZPHI-C2. ZPHI-C1 was infected approximately 2 years earlier, possibly by SHCS-C4.
In cluster E, ZPHI-E1 may have infected ZPHI-E2 8 days after having been infected. The viral load at this potential transmission event was 1 690 000 copies/ml. Both, E1 or E2 may have infected ZPHI-E3 during their recent phase (mean 132 days after infection; max viral load 1039 copies/ml). ZPHI-E4 and ZPHI-E5 likely have been infected by either ZPHI-E2 or ZPHI-E3 after stopping early ART but not by ZPHI-E1 who continued suppressive therapy (Table S2, http://links.lww.com/QAD/A40).
Although the complexity in cluster F with six SHCS patients and seven ZPHI patients prohibited analysis of the transmission dynamics, sources of new infections seem to be untreated chronically infected rather than acutely infected patients. Chronically infected patients SHCS-F8, F9 and F10 did not receive treatment during several years, when ZPHI-F1, ZPHI-F3, ZPHI-F6, ZPHI-F4, ZPHI-F2, ZPHI-F5 and ZPHI-F7 were infected sequentially. All of the latter ones reached undetectable viral load during most of the timepoints when those new infection events happened because they received early ART.
Taken together, these patients demonstrate the importance of using clinical, laboratory and epidemiological data to supplement phylogenetic analysis in the assessment of putative transmission chains . Surprisingly, only in one example transmission may have happened during the acute phase (ZPHI-E1, ZPHI-E2) and in one patient within the recent phase (ZPHI-E3) of the possible source. However, in five other patients, transmission presumably took place while the index patient was already in the chronic stage of infection 109–425 days after interruption of early ART. Notably, under treatment, all patients showed undetectable viral load (except few blips) indicating that adherence to therapy was generally very good. Taking into account the overall time when patients were under virologically suppressive treatment, we estimate that 3.5 [95% confidence interval (CI) 0.9–13.5] infection events per person-year occurred prior to treatment initiation and 1.8 (95% CI 0.5–5.8) events per person-year after cessation of the initial treatment.
In previous studies using phylogenetic reconstruction, patients were categorized as acutely or chronically infected according to their stage at diagnosis but not when transmission actually occurred [5,32]. This probably led to overestimation of transmission frequencies during acute/early infection. Phylogenetic analyses have limitations, as one can never rule out transmissions potentially originating from other index cases not known to the investigator. This effect is attenuated in our setting because the primary HIV infection patients enrolled represent approximately 55% of all newly HIV-infected MSM patients in the canton of Zurich and the likelihood that HIV-infected patients are enrolled in the SHCS is high [21,22]. In contrast to other phylogenetic studies assessing transmission dynamics [5,15,33,34], we used two different samples and analyzed two different genetic regions to increase genetic information and to exclude laboratory and database errors . Moreover, plausibility of the transmission clusters was controlled by longitudinal viral load data.
This study demonstrates that in our intensely studied sexually active MSM, collective preventive safer-sex counselling was insufficient as documented by the high number of new infections originating from patients who stopped early ART according to study protocol. Of note, the same individuals were very adherent to ART. Furthermore, we detected a remarkable proportion of new infections originating from index patients being already in their chronic phase, sometimes with low viral loads. These findings argue strongly for early, continuous ART in sexually active HIV-1-infected MSM. This strategy, most likely, will have a profound impact to reduce the further spread of HIV-1.
This study has been financed in the framework of the SHCS, supported by the Swiss National Science Foundation (SNF #33CSC0-108787). Further support was provided by the SNF grant #3247B0-112594 and #320000-116035 (to H.F.G.), the Union Bank of Switzerland in the name of a donor to H.F.G., unrestricted research grant from Tibotec, Switzerland, the SHCS research foundation and SHCS projects #470 and #528.
We are grateful to all the patients participating in the ZPHI Study and in the SHCS; Barbara Hasse, Urs Karrer, Rolf Oberholzer, Elisabeth Presterl, Reto Laffer, Ulrich von Both, Klara Thierfelder, Dominique Braun, Markus Flepp and Thomas Frey for their dedicated patient care; Friederike Burgener and Dominique Klimpel for excellent laboratory assistance; Christine Vögtli and Ingrid Nievergelt for administrative support. We also would like to thank the UZH IT services for giving us access to the high-performance computer of the University of Zurich. Furthermore, we thank all the staff of the SHCS clinical centers, the data center and all resistance laboratories for their great work and Joseph K. Wong for critical review of the manuscript.
Günthard conceptualized, designed and supervised the study. Data acquisition was done by Rieder, Joos, von Wyl, Kuster, Grube, Leemann, Böni, Yerly, Klimkait, Bürgisser and Günthard. Analysis of the manuscript was done by Rieder, Joos, Günthard, and von Wyl. Critical revision of this article was done by Fischer, Weber, Kuster, Bürgisser, Yerly, Böni and Klimkait.
H.F.G. has been an adviser, consultant or both for the following companies: GlaxoSmithKline, Abbott, Novartis, Boehringer-Ingelheim, Roche, Tibotec and Bristol-Myers Squibb, and has received unrestricted research and educational grants from Roche, Abbott, Bristol-Myers Squibb, GlaxoSmithKline, Tibotec and Merck Sharp & Dohme. S.Y. has participated in advisory boards of Bristol-Myers Squibb and Tibotec, and has received travel grants from GlaxoSmithKline and Merck Sharp & Dohme. V.V.W., P.R., H.K., C.G., C.L., J.B., T.K., P.B., R.W. and M.F. have no conflicts of interest.
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