Epidemiologic and Environmental Investigations of Reported Hantavirus Cases Inform Exposure Risk in California, 1993–2020

From 1993 to 2020, 89 hantavirus cases were reported in California residents. Fifty-six (63%) were male, mean age was 41.5 years old, and 28 (31%) of the cases were fatal. The majority of cases were classified as hantavirus pulmonary syndrome, and infections peaked during summer and spring. A total of 70 environmental investigations were conducted for 77 cases (87%). Visual evidence of rodent activity was detected in 52 (74%) of the investigations, and 36 patients (40%) reported direct contact with rodents or having cleaned rodent-affected areas. In total, 1,353 rodents (73%) captured during the investigations were Peromyscus maniculatus , and 264 (20%) tested positive for Sin Nombre virus (SNV) antibodies. Probable exposure locations were identified for 81 cases (91%), with the majority of exposures occurring in the patient’s county of residence. Indoor exposure was most common, and more exposures occurred in peridomestic environments than at worksites or recreational areas. Epidemiological and environmental investigations and SNV sequencing were crucial in identifying exposure sites. Enhanced awareness and preventive measures, especially in high-risk areas and among at-risk populations, are essential to mitigate future cases.