Marco Labarile, Paul Frischknecht, Tom Loosli, Nadia Neuner-Jehle, Marius Zeeb, Michael Huber, Karoline Leuzinger, Matthieu Perreau, Alban Ramette, Sabine Yerly, Matthias Cavassini, Marcel Stöckle, Eugénie Colin-Benoit, Alexandra Calmy, Patrick Schmid, Marco Bongiovanni, David H-U Haerry, Matthias Egger, Huldrych F Günthard, Chloé Pasin, Roger D Kouyos
{"title":"Trends in HIV-1 transmission in Switzerland: a retrospective molecular epidemiology study.","authors":"Marco Labarile, Paul Frischknecht, Tom Loosli, Nadia Neuner-Jehle, Marius Zeeb, Michael Huber, Karoline Leuzinger, Matthieu Perreau, Alban Ramette, Sabine Yerly, Matthias Cavassini, Marcel Stöckle, Eugénie Colin-Benoit, Alexandra Calmy, Patrick Schmid, Marco Bongiovanni, David H-U Haerry, Matthias Egger, Huldrych F Günthard, Chloé Pasin, Roger D Kouyos","doi":"10.1016/S2352-3018(26)00173-6","DOIUrl":null,"url":null,"abstract":"<p><strong>Background: </strong>The rapid identification of emerging transmission clusters could help reach the 2030 goal of halting transmission of HIV in Switzerland. We characterised the size, structure, and growth of recent HIV-1 transmission clusters in the Swiss HIV Cohort Study (SHCS).</p><p><strong>Methods: </strong>In this retrospective molecular epidemiology analysis in Switzerland, we analysed 32 294 HIV-1 pol sequences from 16 428 SHCS participants, enrolled between Aug 14, 1984, and May 19, 2025. Sequences were aligned and clustered using a 0·01 Tamura-Nei 93 distance threshold, and networks were constructed at the participant level to identify clusters and their growth. We defined and described a set of fast-growing clusters of HIV in Switzerland. Associations between clustering, demographic and clinical characteristics, and viral suppression were assessed.</p><p><strong>Findings: </strong>7387 (45·0%) participants were part of 1131 clusters. Cluster size distribution was highly skewed: 62% contained only two individuals, whereas a few large clusters accounted for thousands of participants. The epidemic fragmented from a single dominant cluster of people who inject drugs in the 1990s into numerous smaller clusters, predominantly among gay, bisexual, and other men who have sex with men (MSM). Since 2016, 32·6% of the total cluster growth was concentrated in a set of 23 fast-growing clusters. These fast-growing clusters mostly comprised western European MSM with high rates of condomless sex. Cluster growth was strongly associated with viraemia among connected participants.</p><p><strong>Interpretation: </strong>The Swiss HIV epidemic has evolved into fragmented, short transmission chains, with a small number of fast-growing clusters sustaining ongoing transmission. Molecular surveillance can identify such clusters, enabling tailored interventions that complement treatment as prevention. Achieving zero HIV transmission in Switzerland will require integration of molecular epidemiology into routine prevention.</p><p><strong>Funding: </strong>Swiss National Science Foundation.</p>","PeriodicalId":48725,"journal":{"name":"Lancet Hiv","volume":" ","pages":""},"PeriodicalIF":14.6000,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Lancet Hiv","FirstCategoryId":"3","ListUrlMain":"https://doi.org/10.1016/S2352-3018(26)00173-6","RegionNum":1,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"IMMUNOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Background: The rapid identification of emerging transmission clusters could help reach the 2030 goal of halting transmission of HIV in Switzerland. We characterised the size, structure, and growth of recent HIV-1 transmission clusters in the Swiss HIV Cohort Study (SHCS).
Methods: In this retrospective molecular epidemiology analysis in Switzerland, we analysed 32 294 HIV-1 pol sequences from 16 428 SHCS participants, enrolled between Aug 14, 1984, and May 19, 2025. Sequences were aligned and clustered using a 0·01 Tamura-Nei 93 distance threshold, and networks were constructed at the participant level to identify clusters and their growth. We defined and described a set of fast-growing clusters of HIV in Switzerland. Associations between clustering, demographic and clinical characteristics, and viral suppression were assessed.
Findings: 7387 (45·0%) participants were part of 1131 clusters. Cluster size distribution was highly skewed: 62% contained only two individuals, whereas a few large clusters accounted for thousands of participants. The epidemic fragmented from a single dominant cluster of people who inject drugs in the 1990s into numerous smaller clusters, predominantly among gay, bisexual, and other men who have sex with men (MSM). Since 2016, 32·6% of the total cluster growth was concentrated in a set of 23 fast-growing clusters. These fast-growing clusters mostly comprised western European MSM with high rates of condomless sex. Cluster growth was strongly associated with viraemia among connected participants.
Interpretation: The Swiss HIV epidemic has evolved into fragmented, short transmission chains, with a small number of fast-growing clusters sustaining ongoing transmission. Molecular surveillance can identify such clusters, enabling tailored interventions that complement treatment as prevention. Achieving zero HIV transmission in Switzerland will require integration of molecular epidemiology into routine prevention.
期刊介绍：
The Lancet HIV is an internationally trusted source of clinical, public health, and global health knowledge with an Impact Factor of 16.1. It is dedicated to publishing original research, evidence-based reviews, and insightful features that advocate for change in or illuminates HIV clinical practice. The journal aims to provide a holistic view of the pandemic, covering clinical, epidemiological, and operational disciplines. It publishes content on innovative treatments and the biological research behind them, novel methods of service delivery, and new approaches to confronting HIV/AIDS worldwide. The Lancet HIV publishes various types of content including articles, reviews, comments, correspondences, and viewpoints. It also publishes series that aim to shape and drive positive change in clinical practice and health policy in areas of need in HIV. The journal is indexed by several abstracting and indexing services, including Crossref, Embase, Essential Science Indicators, MEDLINE, PubMed, SCIE and Scopus.
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