1993 Four Corners hantavirus outbreak

An outbreak of hantavirus disease occurred in 1993 in the United States, primarily in the Four Corners region of Arizona, Colorado, and New Mexico. Before 1993, hantaviruses that cause disease in humans, native to rodents, were known to spread mainly in Asia and Europe and to cause hemorrhagic fever with renal syndrome. The outbreak in 1993 led to the discovery of hantaviruses from the Western Hemisphere that could cause disease and revealed the existence of a second disease caused by them: hantavirus pulmonary syndrome (HPS). In the Four Corners states, 17 of the 33 HPS cases in 1993 resulted in death, a 52% case fatality rate. Nationwide that year, 27 of the 48 HPS cases resulted in death, a 56% case fatality rate.

The earliest confirmed cases of HPS in 1993 occurred in March, but the outbreak was not discovered until May when a young Navajo couple died within days of each other due to sudden respiratory failure. Investigators quickly found other people with the same symptoms as the couple. Further investigation discovered a new hantavirus, Sin Nombre virus (SNV), as the cause and identified the western deer mouse as its natural reservoir. Public health officials gave advice on how to prevent infection, and the antiviral drug ribavirin was tested on suspected cases. While the first cases to be identified were in the Four Corners region, more cases were identified outside of the area as the year went on but not in the Four Corners state Utah. Before research in 1993 showed that SNV was not spread between people, there was widespread fear that HPS was contagious. Consequently, Native Americans of the Four Corners region, especially the Navajo, experienced discrimination and racism during the outbreak.

The 1991–1992 El Niño indirectly caused the outbreak by producing a warmer-than-usual 1992–1993 winter and increased rainfall in the spring of 1993 in the Four Corners region. This increased the amount of vegetation available for rodents for food and shelter, which led to a significant increase in their numbers. The increased population density of rodents allowed SNV to spread more easily, and with a much larger population, interactions with people were more likely to occur. Further research has uncovered HPS cases before the outbreak as far back as 1959. Since the outbreak, hantaviruses that cause HPS have been identified throughout the Americas. In North America, SNV is the most common cause of the disease. HPS infections are rare, but they have a case fatality rate ranging from 12% to 45%, varying by virus. Treatment is supportive, and prevention is based on minimizing contact with rodents.