First recognized hantavirus pulmonary syndrome outbreak in the Americas. Led to identification of Sin Nombre virus and its reservoir, the deer mouse.
In May 1993, otherwise healthy young adults in the Four Corners region (Arizona, New Mexico, Colorado, Utah) began presenting with rapidly fatal acute respiratory distress syndrome of unknown cause. Within weeks, CDC investigators traced the outbreak to a previously unknown hantavirus, later named Sin Nombre virus, with the deer mouse as its reservoir.
The outbreak transformed hantavirus epidemiology. Until 1993, hantaviruses were thought to cause only renal syndromes (HFRS) in Asia and Europe. The Four Corners cases established the existence of HPS and led to recognition of multiple New World hantaviruses across the Americas.
Investigators tied the outbreak to an explosion in deer mouse populations driven by a wet El Niño year that produced abundant piñon nuts. Increased rodent populations in and around homes led to elevated human exposure through aerosolized excreta during spring cleaning of long-closed cabins and structures.