The first recognized hantavirus pulmonary syndrome outbreak in the Americas. Investigation led to the identification of Sin Nombre virus and established the deer mouse as its reservoir host.
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 (Peromyscus maniculatus) as its reservoir [1] [2].
The outbreak transformed hantavirus epidemiology. Until 1993, hantaviruses were thought to cause only hemorrhagic fever with renal syndrome (HFRS) in Asia and Europe. The Four Corners cases established the existence of hantavirus pulmonary syndrome (HPS) and led to the recognition of multiple New World hantaviruses across the Americas [1].
The CDC, Indian Health Service, New Mexico Department of Health, and University of New Mexico jointly conducted the field investigation. PCR analysis of patient samples and trapped rodents identified Sin Nombre virus, with strong sequence similarity between human samples and deer mouse samples confirming the zoonotic reservoir [1] [2].
Investigators tied the outbreak to an explosion in deer mouse populations driven by a wet El Niño year that produced abundant piñon nuts and other food sources. Increased rodent populations in and around homes led to elevated human exposure through aerosolized rodent excreta, particularly during spring cleaning of long-closed structures [2].