The largest documented person-to-person Andes virus transmission event in history. 34 cases, 11 deaths, traced through three identifiable generations of transmission originating at a birthday celebration in Epuyén, Chubut Province, Argentina.
The Epuyén outbreak in Chubut Province, Argentina, between November 2018 and February 2019 remains the most thoroughly documented person-to-person hantavirus transmission event ever recorded. The outbreak originated at a birthday celebration on 25 November 2018; the index case fell ill several days later and the cluster subsequently propagated through three identifiable generations of transmission before being contained by aggressive contact tracing and case isolation by Argentine and Chilean health authorities. The definitive case series and transmission analysis was published in the New England Journal of Medicine in December 2020 by Martinez et al. [1].
The outbreak transformed clinical understanding of Andes virus. Although person-to-person transmission had been suspected since the 1996 El Bolsón cluster in the same region of Argentina, Epuyén provided the resolution to trace generations of cases with molecular and epidemiological confidence. The 2020 NEJM analysis remains the reference for hantavirus interpersonal transmission biology and informs current contact-tracing protocols including those deployed during the 2026 MV Hondius cluster [1].
A single individual exposed to long-tailed pygmy rice rat (the Andes virus reservoir, Oligoryzomys longicaudatus) attended a birthday celebration on 25 November 2018, fell ill in the days that followed, and died [1].
Among approximately 25 attendees of the birthday party, multiple cases developed within 2-4 weeks. Several attended the funerary wake of the index case, where additional transmission occurred [1].
Household members of generation-2 cases who did not attend the birthday party, including healthcare workers without adequate PPE and intimate partners, formed the third transmission ring. The NEJM analysis identified specific super-spreader individuals through molecular and contact-tracing analysis [1]. Containment was achieved through aggressive contact tracing and isolation directed by Argentine national health authorities in coordination with Chilean counterparts.
The same region of Argentina experienced an earlier hantavirus cluster in 1996 in El Bolsón, Río Negro. That cluster, comprising 16 epidemiologically linked cases, was the first event globally for which person-to-person transmission of any hantavirus was suspected. The strain involved in 1996 (subsequently designated Epilink/96) is virologically similar to the Epuyén/18-19 strain, suggesting a stable circulating Andes virus lineage in northern Patagonia [2]. The 1996 El Bolsón findings remained controversial in the literature until the 2020 NEJM Epuyén analysis provided definitive molecular confirmation of human-to-human Andes virus transmission.