The 18 Americans now being monitored following exposure to the andes hantavirus strain aboard a cruise ship may not show symptoms for up to 42 days after exposure — a lengthy window that complicates containment and has direct implications for hospital leaders around planning capacity, resource allocation and who may encounter cases in the weeks ahead.
Why 42 days?
The Andes virus has “a much longer incubation period than we see for a lot of other viruses,” Brendan Jackson, MD, acting director of the CDC’s Division of High-Consequence Pathogens and Pathology, said in a May 12 press conference at University of Nebraska Medical Center — where 16 passengers are currently being monitored.
The CDC’s Health Alert Network advisory, issued May 8, puts the incubation range at four to 42 days, with most patients becoming symptomatic during the second to fourth week after exposure. Greg Mertz, MD, a physician and professor emeritus of internal medicine at the University of New Mexico in Albuquerque who has studied hantaviruses for decades, told Scientific American there is a possibility the incubation period could extend to seven weeks, though that is uncommon.
That window is driven by how the virus behaves in the body. Unlike influenza or SARS-CoV-2, which replicate quickly in the upper airways and trigger rapid immune responses, Andes virus quietly circulates in the bloodstream before infiltrating endothelial cells lining blood vessels — primarily in the lungs — where it replicates without immediately provoking an immune response. Inflammation and fluid buildup in the lungs follow over time, eventually causing the respiratory distress that defines hantavirus pulmonary syndrome.
“You can tell from influenza that local infection starts in the upper respiratory tract,” Dr. Mertz told Scientific American. That is less clear with Andes virus, which can cause “widespread infection without developing an immune response at first.”
The viral dose matters too. Daniel Pastula, MD, chief of neuroinfectious diseases and global neurology at the University of Colorado Anschutz, told Scientific American that the larger the initial exposure — whether through aerosolized rodent feces, close contact with a symptomatic person or exposure to bodily fluids — the faster the onset of symptoms may occur.
What the 42-day window means for hospitals
The extended incubation period has already strained the nation’s specialized biocontainment infrastructure. UNMC’s biocontainment unit lacked the capacity to house all returning passengers, requiring two individuals to be transferred to Emory University’s Serious Communicable Diseases Unit — one of only a handful of facilities in the country equipped for this level of care. That capacity constraint, with a patient population of just 18, is a signal worth noting for health system leaders thinking about surge scenarios.
HHS officials said asymptomatic passengers will be permitted to complete the 42-day monitoring period at home — a practical necessity given facility limitations, but one that increases the likelihood that community hospitals and health systems outside Nebraska and Georgia could encounter a case. UNMC medical director Angela Hewlett, MD, said she “highly” encourages passengers to stay for the full period, citing on-site testing capability and the ability to respond immediately if anyone deteriorates — advantages she noted are not available at most other facilities.
For those health systems, the CDC’s HAN advisory outlines specific requirements: Patients with suspected or confirmed Andes virus infection should be placed in an airborne infection isolation room, with staff using gowns, gloves, eye protection and an N95 or higher-level respirator.
The long incubation also creates a compounding diagnostic problem: Early detection is also unreliable. Diagnosis within the first 72 hours of symptoms is difficult before the virus can be accurately detected in body secretions, and recommends repeat testing at the 72-hour mark. CLIA assays for New World hantavirus IgM and IgG antibodies are available at CDC, some state public health labs and Quest Diagnostics.
The treatment picture adds another layer of complexity. There is no specific antiviral treatment; care is entirely supportive. Critically ill patients can deteriorate rapidly, and the CDC advisory notes that ECMO can improve survivability to roughly 80% if initiated early. But not all hospitals have ECMO capability, and for those that don’t, transfer protocols for a patient in a biocontainment-level situation require advance planning.
More cases may still emerge
The 42-day window means the hantavirus outbreak is not over from a case-count standpoint, and hospital leaders should plan accordingly. Studies have shown the virus can be present in blood and other bodily fluids up to 14 days before a patient becomes symptomatic — according to a 2007 study in Chile that Dr. Mertz co-authored tracking 76 infected patients and 476 household contacts. Whether Andes virus can be transmitted before symptom onset remains an open question, Dr. Pastula told Scientific American.
That ambiguity is driving the aggressive monitoring response. The Kansas Department of Health and Environment is tracking three individuals with high-risk exposure to a confirmed case who were never aboard the ship. The Minnesota Department of Health is monitoring one person who had brief overseas exposure to a Hondius passenger, and an additional 12 U.S. residents are being monitored by state health departments — none are currently symptomatic.
The global case counts stand at 11. The World Health Organization says there have been no new deaths since May 2. With the incubation clock still running for dozens of contacts worldwide, that number could rise before the picture clears — and with it, the possibility that a case walks through the doors of a hospital with no specialized biocontainment infrastructure and no prior preparation.
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