2026 Hantavirus Outbreak: Testing for Potential Infection

This message is being sent to the health alert network, local public health officers, Tribal health directors, local public health department nurses, local public health department staff, and infection preventionists.

Key points 

• On May 18, 2026, the CDC (Centers for Disease Control and Protection) issued a Health Alert Network (HAN) 2026 Hantavirus Outbreak: Testing for Potential Infection after an outbreak of Andes virus, a hantavirus endemic in areas of South America, was identified among cruise ship passengers.
• The overall risk to the American public is still considered extremely low at this time. CDC and health departments in several states are monitoring the health of U.S. passengers from the ship and U.S. air travel contacts of symptomatic ship passengers who were subsequently confirmed to have Andes virus infection.
• As of May 20, 2026, no confirmed cases of Andes virus associated with the outbreak on the cruise ship have been reported in the United States.
• The Wisconsin Department of Health Services (DHS) is providing clinicians and health departments considerations for hantavirus testing and what testing is available for patients with suspected hantavirus infection, including Sin Nombre virus, which is endemic to Wisconsin, and Andes virus, which is not.
• Hantaviruses are a group of viruses that typically spread to people who come in contact with sylvatic rodents. These viruses can cause severe illness or death in humans. Andes virus is the only type of hantavirus that is known to spread from person to person.
• Several other New World hantaviruses are endemic to the United States, including Wisconsin, and are not transmissible from person to person. New World hantaviruses can cause hantavirus pulmonary syndrome (HPS), a potentially serious disease that can cause damage to the lungs.

Background

On May 2, 2026, the World Health Organization (WHO) was notified of a cluster of severe acute respiratory illness (SARI) among passengers and crew aboard the M/V Hondius cruise ship in the Atlantic Ocean. On May 6, 2026, WHO confirmed that the cluster was caused by Andes virus, a hantavirus endemic in areas of South America that can cause HPS. Andes virus is the only hantavirus known to spread from person to person. This type of transmission is rare for hantaviruses and is generally associated with prolonged close contact. As of May 20, WHO has reported 11 cases (nine of them laboratory-confirmed), including three deaths.

Hantaviruses cause two syndromes:

• HPS: Hantaviruses found in the Western Hemisphere are often referred to as New World hantaviruses and can cause HPS. Several New World hantaviruses that do not spread person to person are endemic in the United States. These include Sin Nombre virus, the virus mostly commonly associated with U.S. HPS cases.
• Hemorrhagic fever with renal syndrome (HFRS): A group of clinically similar illnesses that affect the kidneys. HFRS is caused by another group of hantaviruses, often referred to as Old World hantaviruses, that are found mostly in Europe and Asia. However, Seoul virus, a type of hantavirus that causes HFRS, is found worldwide, including in the United States.
• Non-HPS hantavirus infection can also occur, in which patients experience non-specific viral symptoms without cardio-pulmonary symptoms.

Sin Nombre virus is present in Wisconsin deer mice. Human cases have occurred, with the most recent case in 2025. During 2016–2017, an outbreak of Seoul hantavirus infection occurred in the Midwest, including Wisconsin, among people who had contacts with captive bred rats.

Hantavirus infections can occur year-round but are reported more frequently during the spring and summer months when rodent populations increase and people may have greater exposure to rodent-infested environments such as cabins, sheds, campsites, and homes. The most common hantavirus that causes HPS in the United States is spread by the deer mouse. Andes virus is spread primarily by the long-tailed pygmy rice rat (Oligoryzomys longicaudatus).

Recommendations for clinicians 

• Consider Andes virus infection in patients who
  • (1) have symptoms compatible with hantavirus infection, and
  • (2) were aboard the M/V Hondius cruise ship or had direct contact with someone associated with the M/V Hondius Andes virus outbreak.
• Contact DHS or your local or Tribal health department immediately to report a suspected Andes virus case and for assistance with diagnostic testing for Andes virus.
• Know that assays designed to specifically detect Andes virus may not detect other New World hantaviruses endemic in the United States.
• Consider infection with other New World hantaviruses in patients who
  • (1) have symptoms compatible with HPS or non-HPS hantavirus infection*, and
  • (2) have a history of known or suspected exposure to sylvatic rodents or rodent excreta (for example, urine, droppings, or nesting materials).
• Contact DHS or your local or Tribal health department immediately to report a suspected New World hantavirus case and for assistance with diagnostic testing for patients highly suspected of HPS or non-HPS hantavirus infection. Because of the probability of false positive IgM serologic assays, consultation with DHS is highly recommended prior to submission of specimens to commercial laboratories.
• Progressive thrombocytopenia is one of the most consistent laboratory findings in New World hantavirus infection occurring in nearly all patients. Thrombocytopenia is frequently present during the prodrome phase. An unconcerning complete blood count (CBC) and peripheral blood smear may provide reassurance to patients who have a history of rodent exposure and have mild nonspecific symptoms.
• Consider infection with Old World hantaviruses in patients who
  • (1) have symptoms consistent with HFRS, and
  • (2) have a history of known or suspected exposure to sylvatic rodents or rodent excreta (for example, urine, droppings, or nesting materials).
• Test for non-Andes hantavirus in patients who have symptoms compatible with hantavirus infection and have a history of rodent exposure, but who are not associated with the M/V Hondius Andes virus outbreak.

*Patients with New World hantavirus infection typically present in a nonspecific way with a relatively short febrile prodrome lasting 3–5 days. In addition to fever and myalgias, early symptoms include:

• Headache
• Chills
• Dizziness
• Non-productive cough
• Nausea
• Vomiting
• Other gastrointestinal symptoms

Malaise, diarrhea, and lightheadedness are reported by approximately half of patients, with less frequent reports of arthralgias, back pain, and abdominal pain. Typical clinical laboratory findings include hemoconcentration, left shift in the white blood cell count, neutrophilic leukocytosis, thrombocytopenia, and circulating immunoblasts. Progression to cardio-pulmonary symptoms occurs in most patients consistent with HPS.

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