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 theoutbreak.
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 thedisease. 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.
Background
The Four Corners refers to the region surrounding the four-state border between southwestern Colorado, northwestern New Mexico, northeastern Arizona, and southeastern Utah. Most of the area is divided into reservations for Native American nations and tribes, namely the Navajo Nation, Hopi Reservation, Ute Mountain Ute Tribe, Southern Ute Indian Reservation, Zuni Indian Reservation, and Jicarilla Apache Nation. Thissparsely populated area is part of the Colorado Plateau, a desert region with mountains, canyons, and sedimentary rock formations.
Hantaviruses are a group of viruses that constitute the taxonomic family Hantaviridae. Hantaviruses that cause disease in humans are native to rodents and assigned to the genus Orthohantavirus. Each species of hantavirus is usually transmitted by one rodent species. Before the 1993 Four Corners outbreak, Old World hantaviruses were known to cause hemorrhagic fever with renal syndrome (HFRS) and nephropathia epidemica, a milder form of HFRS, in Asia and Europe. Before this outbreak, New World hantaviruses were not known to infect or cause illness in humans.
Course of outbreak
After HPS was discovered in May 1993, the outbreak was confirmed to have started earlier, in March. A dozen more cases were reported, mostly among the Navajo, in the weeks after the discovery. The outbreak continued to worsen through June and peaked in July before a sharp decline in August. HPS was first reported outside the Four Corners in Texas, in June. By mid-August, 23 hantavirus infections had been confirmed in the Four Corners region. In the Southwest, 20 of the 30 confirmed cases resulted in death, a 67% case fatality rate. As the year went on, an increasing number of cases were identified outside the Four Corners region. By October, 60 cases of hantaviral disease had been reported nationwide, about half in the Four Corners region. Thirty-nine of these cases were confirmed by laboratory testing, 25 of which led to death.
From August to December, new reports of HPS were relatively low, except for a spike in October. By the end of the year, 48 cases had been confirmed nationwide, 27 of which resulted in death. This 56% case fatality rate was similar across age, sex, and race, and it declined as physicians learned to quickly recognize HPS, identify less severe cases, and effectively treat HPS. Most of the infected were male, and, in the Four Corners region, all of the infected either lived in or visited rural areas before falling ill. Of the 33 cases to occur in 1993 in Arizona, Colorado, and New Mexico, 26 occurred during the height of the outbreak from April to July, and 17 died, a 52% case fatality rate. The only Four Corners state where no HPS was identified in 1993 was Utah.
Outbreak investigation Discovery On May 11, 1993, a 19-year-old Navajo man, a competitive long-distance runner, visited the hospital in Crownpoint, New Mexico, for fever, muscle pain, chills, headache, and malaise. He was given an antibiotic, a drug for influenza A, and a painkiller and discharged from the hospital. He returned two days later due to persistent symptoms, vomiting, and diarrhea and was discharged with no change in treatment. On the morning of May 14, he was traveling with his family from Crownpoint to Gallup, New Mexico, when he became severely short of breath. They stopped their car in Thoreau, New Mexico, about 30 miles (42km) east of Gallup, and contacted emergency services. By the time help arrived, he had collapsed due to respiratory failure. An ambulance crew performed CPR as he was taken to the Gallup Indian Medical Center, where he was found to have fluid buildup in his lungs (pulmonary edema). Despite efforts to resuscitate him, he died. The death of the young man due to sudden respiratory failure confused medical staff.
Because the man's death was highly unusual, it was required by law to be reported to the New Mexico Office of the Medical Investigator (OMI) inAlbuquerque, where autopsies are conducted. The deputy medical investigator in Gallup, Richard Malone, was called in to investigate hisdeath. Malone had investigated a similar death of a 30-year-old Navajo woman a few weeks earlier, in April, at the same medical facility inGallup. The woman's death, attributed to pulmonary edema, was examined post mortem by University of New Mexico (UNM) pathologist Patricia McFeeley, who worked with the New Mexico OMI. The woman's lungs were filled with blood plasma and more than twice as heavy as usual. Test results were negative for known infections that could have caused her death. Malone contacted McFeeley on the day of the man's death to discuss the similarities between the two cases, and she agreed to perform an autopsy on the deceased man once permission was obtained from his family.
Malone spoke to the parents of the deceased man and hoped to receive information about what could have caused his death. They told Malone that their son collapsed while they were on their way to the funeral of his fiancée. She had died five days earlier, on May 9, at the hospital in Crownpoint with the same symptoms as her fiancé. Since Crownpoint is on the Navajo reservation, the medical facility there was not required to report her death to the New Mexico OMI and did not do so. Furthermore, due to her history of asthma, her death was not considered alarming at first. After updating McFeeley on the situation, Malone convinced the families of the deceased to have the couple's bodies examined in autopsy. Later that day, McFeeley reported a possible outbreak of an unknown and deadly respiratory illness to the state health department in Santa Fe and prepared for autopsy. The autopsies of the couple showed only severe pulmonary edema with no explanation for the cause ofillness.
Expanded scope
Malone then contacted Bruce Tempest, the medical director of Gallup Indian Medical Center. Tempest recalled having been involved in at least two discussions with physicians who had cared for young, previously healthy tribal members who suddenly died from an unknown respiratory illness. Malone and Tempest agreed that the situation required further action, so they searched for more cases. Tempest was aware of the three recent cases in New Mexico as well as one from the previous November in Arizona. Health officials in Arizona informed him of another recent case, so on May 17, Malone and Tempest notified the New Mexico Department of Health of their concerns. State officials notified the Centers for Disease Control and Prevention (CDC) on May 18 and began an investigation with the Indian Health Service (IHS) and the Navajo Nation's health department. They examined the homes of the deceased and interviewed their families and the physicians who had cared for them. On May 24, New Mexico state officials sent a letter to clinicians in the Four Corners states that described the illness and situation and asked for any similar cases to be reported to them immediately, which identified several potential cases.
After learning of the situation, the press reported on May 27 that an unknown disease was killing young tribal members in the Four Corners, which caused great anxiety in the public. Navajo and Hopi people were ostracized from the rest of society, and politicians faced pressure to respond to the situation. On the same day, New Mexico state officials contacted the CDC and asked for assistance. On May 28, a team of investigators was created and Jay Butler, an epidemiologist at the CDC's Epidemic Intelligence Service, was made the leader of the team. Less than a day later, the group arrived at Albuquerque and was transported to the University of New Mexico. There, they were joined by members of the UNM medical faculty, IHS physicians, infectious disease and toxicology experts, physicians who had treated the deceased, and various state and national health officials. Robert Breiman, a respiratory disease expert, was selected to lead the field investigation, while C. J. Peters, the head of the CDC's Special Pathogens Branch, was put in charge of the laboratory work being done at the CDC in Atlanta, Georgia.
In a meeting that took place from May 29 to May 31, the task force agreed to evaluate any person in the area from January 1, 1993, onward who had radiological imaging that showed evidence of unexplained excess substances in both lungs (bilateral infiltrates) with low levels of oxygen in the blood (hypoxemia) as well as any death accompanied with unexplained pulmonary edema. Thegroup received clinical information about more than 30 suspected cases and considered various causes of illness. Plague, tularemia, and anthrax, among other diseases, were eliminated from consideration due to lack of evidence. The team believed the outbreak to be caused by either a new, aggressive form of influenza, an environmental toxin, or a previously unrecognized pathogen.
Hantavirus suspected