The US Centers for Disease Control and Prevention is monitoring 41 people in the US for the Andes hantavirus after a cruise ship was hit with a rare outbreak but that the risk to the public remains low.

This includes a group of 18 passengers from the cruise ship who are now in quarantine facilities in Nebraska and Georgia, according to health officials. The agency is also monitoring passengers who returned home before the outbreak was identified and others who were exposed during travel, specifically on flights where a symptomatic case was present.

“Most people under monitoring are considered high-risk exposures, and CDC recommends that everyone under monitoring stay at home and avoid being around people during their 42-day monitoring period,” David Fitter, incident manager for the CDC’s hantavirus response, told reporters during a media briefing on Thursday. “We emphasize not to travel across all these groups.”

The Andes virus is a strain of hantavirus found in South America that can be transmitted from person to person. Typically, hantavirus is passed to humans when they come into contact with rodent droppings or urine. A respiratory virus, the disease can cause difficulty breathing and carries a fatality rate of around 35 percent. As of Thursday, the World Health Organization has confirmed 11 cases of the Andes virus among passengers of the MV Hondius cruise ship, including three deaths.

A Department of Health and Human Services official confirmed to WIRED that all Americans who were on board the Hondius at any point during its journey are now back in the US.

The CDC has legal authority to issue federal quarantine and isolation orders to prevent the spread of certain communicable diseases into or within the US. Fitter said on Thursday that the CDC is not using that authority to manage all 41 of the individuals who were potentially exposed to the hantavirus.

“Our approach is based on risk and evidence,” he said. “We are working closely with passengers and public health partners to ensure monitoring and rapid access to care if symptoms develop. Our goal is to work with them and alongside them, building plans based on their specific situations to protect the health and safety of passengers and American communities.”

Individuals will be monitored for 42 days, which is the amount of time it can take for hantavirus symptoms to appear after exposure. Symptoms begin as flu-like, with fever, muscle aches, and fatigue, then rapidly progress to severe respiratory distress.