What was the 1993 Four Corners hantavirus outbreak?

In May 1993 a cluster of previously healthy young adults in the Four Corners region (where New Mexico, Arizona, Colorado and Utah meet) presented with severe, rapidly fatal respiratory failure. Indian Health Service physicians on the Navajo Nation flagged the cluster to the New Mexico Department of Health and the CDC.

By June, CDC and Special Pathogens Branch teams had identified a novel hantavirus by PCR and serology. The pathogen was eventually named Sin Nombre virus (SNV) ("nameless virus"). Its reservoir was the deer mouse (Peromyscus maniculatus). Local Navajo elders reportedly recognised the disease pattern and linked it to abundant rodents following a heavy piñon nut harvest — an ecological connection scientists later confirmed: an El Niño-driven precipitation surge had triggered a deer-mouse population boom.

The outbreak's clinical syndrome was new to medicine: a brief flu-like prodrome followed by precipitous pulmonary oedema and shock. It was named Hantavirus Pulmonary Syndrome (HPS). The case-fatality ratio of the original cluster exceeded 60%; with modern intensive care it is closer to 35–40%.

Four Corners 1993 is the founding event of New World hantavirology. It catalysed surveillance across the Americas and led to the discovery of dozens of additional hantaviruses — including Andes virus in Argentina (1995) and Bayou and Black Creek Canal in the US — over the following decade.