1993 Four Corners hantavirus outbreak

The 1993 Four Corners hantavirus outbreak was an outbreak of hantavirus disease in the United States in the Four Corners region of Arizona, Colorado, and New Mexico. Hantaviruses that cause disease in humans are native to rodents and, before the outbreak, were mainly found in Asia and Europe. Previously, however, they were only known to cause hemorrhagic fever with renal syndrome. The outbreak in the Four Corners region led to the discovery of hantaviruses from the Western Hemisphere that could cause disease and revealed the existence of a second disease caused by hantaviruses: hantavirus pulmonary syndrome (HPS). Thirty-three HPS cases were confirmed in the Four Corners states in 1993, with 19 deaths (58%). Nationwide, 48 cases were confirmed, 27 of which (56%) resulted in death.

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, and further investigation discovered a new hantavirus as the agent responsible, Sin Nombre virus (SNV), 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. Most cases in 1993, including the first cases to be identified, were in the Four Corners region. As the year went on, an increasing number of cases were identified outside of the area. Before research 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 deer mice for food and shelter, which led to a 10-fold increase in their numbers. The increased population density of deer mice 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 South America, Andes virus is the main cause of the disease, whereas in North America, SNV remains the most common cause of HPS. Infection is rare but has a case fatality rate of around 40%. Treatment is supportive, and prevention is based on avoiding and minimizing contact with rodents.