The U.S. Centers for Disease Control and Prevention is expected to publish a formal health advisory on Wednesday elevating its risk assessment for Andes virus, the hantavirus strain linked to a cluster of deaths among passengers and crew aboard the MV Hondius expedition cruise ship, according to public health officials familiar with the agency's review process. The advisory will specifically address the strain's documented capacity for human-to-human transmission — a characteristic that distinguishes Andes virus from nearly all other hantavirus species, which typically spread only through contact with infected rodents.

The MV Hondius, an expedition vessel operated by Oceanwide Expeditions that travels to Patagonia and Antarctic regions, became the focal point of international concern after multiple cases of severe respiratory illness consistent with hantavirus pulmonary syndrome were identified among those aboard. Argentine and Chilean health authorities, whose jurisdictions include the Patagonian regions where Andes virus is endemic, have been coordinating with the CDC and the Pan American Health Organization to trace contacts and assess the full scope of the cluster.

The CDC advisory is anticipated to recommend that healthcare providers in the United States who encounter patients with recent travel to southern South America and unexplained acute respiratory distress consider Andes virus in their differential diagnosis. It will also urge clinicians to implement standard and contact precautions immediately upon suspicion, given the human-to-human transmission risk. The agency is expected to stop short of declaring a formal public health emergency, framing the risk to the general U.S. population as low but stressing vigilance among returning travellers.

Public health experts note that Andes virus human-to-human transmission has been documented in close household contacts, particularly intimate partners, in previous Argentine and Chilean outbreaks. The cruise ship setting — where passengers share confined spaces over extended periods — presents an epidemiological profile that warrants heightened scrutiny. The Pan American Health Organization confirmed Monday it was actively supporting both Argentina and Chile in the investigation and has asked member states to report any suspected imported cases promptly.

The advisory comes as the CDC is already managing a separate norovirus investigation aboard the Caribbean Princess cruise ship, placing the agency's cruise ship health oversight unit under unusual simultaneous pressure. Public health officials said the two investigations are unrelated but that the concurrent cases underscore the agency's role in monitoring disease transmission in maritime environments. The World Health Organization is separately expected to issue a Disease Outbreak News update on the Andes virus cluster later this week.