El Bolsón, Río Negro, Argentina

Cluster of 20 hantavirus pulmonary syndrome cases in El Bolsón and the surrounding Patagonian communities of Bariloche and Esquel between 22 September and 5 December 1996. Eighteen cases occurred among residents or visitors to the affected towns; two additional cases occurred in contacts of El Bolsón patients who had no exposure to the area itself — providing the first documented evidence of person-to-person hantavirus transmission. The implicated agent was Andes virus, with an approximately 50% case-fatality rate.