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BACKGROUND: Hantavirus pulmonary syndrome (HPS) is a severe, frequently fatal, respiratory disease caused by inhalation of sin nombre virus (SNV) in aerosolized excreta from infected deer mice. During June–August, two cases of HPS among Yosemite National Park (YOSE) visitors were reported. Because HPS clusters are rare, we investigated the extent and source of disease.
METHODS: Cases were defined as any febrile illness with SNV antibodies or antigens after lodging at YOSE during June 1–August 28. Patients were located through YOSE visitor notifications and clinician health alerts. We reviewed clinical data and YOSE lodging records, and interviewed patients. We compared the number of cases by lodging type by using Fisher’s exact test. We examined lodging facilities for rodent activity and collected mice for SNV serology.
RESULTS: Among 10 patients identified, nine experienced respiratory illness and three died. Median age was 44.5 years (range: 12–56). One had stayed in an area previously associated with HPS cases. Nine stayed in Curry Village (CV), an area not previously associated with HPS. All nine had stayed in signature tent cabins (STC), which differ from regular tent cabins in having an insulated shell. At CV, nine cases among 8,719 STC lodgers were reported, compared with none among 40,288 regular tent cabin lodgers (P <0.001). Rodent infestations were common in STC insulated spaces. Of 185 traps placed at CV during August, 73 (39%) successfully trapped deer mice; 14% were SNV-seropositive.
CONCLUSIONS: SNV-infected deer mice were present in CV. Infestation of insulated spaces likely increased the risk for hantavirus transmission in STCs, leading to this outbreak. All STCs were closed indefinitely, and multifaceted rodent exclusion and control measures were implemented.