The U.S. Centers for Disease Control and Prevention on Saturday issued expanded surveillance guidance to state and territorial health departments after confirming that 41 people across multiple states are currently being monitored for hantavirus exposure, according to federal public health officials. The updated protocol instructs state laboratory directors to expedite serology testing and to report any suspect cases within 24 hours, a faster turnaround than the previous 48-hour standard.

The CDC's Division of Vector-Borne Diseases, based in Fort Collins, Colorado, is coordinating the response. Officials stressed that hantavirus pulmonary syndrome, though rare, carries a case fatality rate of approximately 38 percent, making rapid identification of additional contacts a public health priority. The agency declined to specify which states account for the highest concentrations of monitored individuals, but epidemiologists familiar with the situation indicated that cases are clustered in the Southwest and Mountain West regions, consistent with the known range of the deer mouse, the primary reservoir for Sin Nombre virus in the United States.

Public health authorities emphasised that human-to-human transmission of North American hantavirus strains remains exceptionally rare and is not considered a driver of the current monitoring effort. Exposure is believed to stem from contact with rodent droppings or nesting materials, and several cases under review involve occupational or recreational settings such as camping sites, agricultural structures, and rural cabins in areas that were inaccessible during winter months and recently reopened in spring.

The National Association of County and City Health Officials welcomed the CDC's updated guidance, noting that state-level capacity for hantavirus testing varies significantly. Officials in New Mexico, Arizona, and Colorado — states with historically the highest incidence rates — confirmed they had received the updated federal protocols and were briefing county health officers. The Indian Health Service, which serves communities in regions where hantavirus exposure risk is elevated, said it was coordinating closely with the CDC to ensure rapid specimen processing for tribal health clinics.

Epidemiologists cautioned against public alarm, noting that the monitoring of 41 contacts does not imply 41 confirmed cases; most individuals under surveillance are expected to test negative. The CDC said it would provide a public update early next week once additional laboratory results are available, and urged residents in affected regions to take standard precautions including sealing rodent entry points in homes and using appropriate protective equipment when cleaning enclosed spaces that may harbour rodent activity.