The 2023 Westerdam Cruise Ship Hantavirus Cases

In March 2023, four passengers on the Westerdam cruise ship tested positive for hantavirus after the ship docked in San Diego. This was unusual because hantavirus is not typically spread person-to-person on ships. Instead, the passengers contracted the virus from infected rodent droppings, urine, or saliva that were present somewhere on the vessel — most likely in a storage area, engine room, or other space where rodents had nested.

Hantavirus does not spread through the air in the way cold or flu viruses do. A person must come into direct contact with contaminated material or breathe in dust from dried rodent waste. On a cruise ship, this usually happens when crew members clean or work in areas where rodents have been active, or when passengers unknowingly touch contaminated surfaces.

The Westerdam cases were investigated by the Centers for Disease Control and Prevention (CDC) and California health officials. They confirmed that rodent activity had occurred on the ship, though the exact location where passengers were exposed was not publicly disclosed in detail.

Key Takeaways

  • Hantavirus on cruise ships comes from infected rodents living in storage areas or engine rooms, not from other passengers or crew members.
  • The virus spreads when a person breathes in dust from dried rodent droppings or urine, or touches contaminated surfaces without protection.
  • Cruise ships are vulnerable to rodent infestation because they carry food, have many enclosed spaces, and dock in ports where rodents live.
  • The 2023 Westerdam outbreak affected four passengers and led to increased rodent control measures across the cruise industry.
  • Symptoms of hantavirus can take two to four weeks to appear, so people who were on the ship may not have known they were exposed until later.

Why Rodents Live on Cruise Ships

Cruise ships are attractive to rodents for the same reason they are attractive to humans: food, water, and shelter. Ships carry thousands of tons of food in storage holds, pantries, and galleys. They have warm engine rooms, cargo bays, and wall cavities where rodents can nest undisturbed. Rodents board ships at port — they climb ropes, hide in cargo containers, or slip through gaps in the hull when the ship is docked.

Once aboard, rodents can survive for months. They reproduce quickly in the warm, dark spaces below deck. A single pair of mice can produce dozens of offspring in a few months. Crew members may not notice the infestation until rodent droppings appear in food storage areas or until someone becomes sick.

Cruise lines use pest control measures — traps, poison, and regular inspections — but no method is 100 percent effective on a ship at sea. Once a ship leaves port, it is difficult to bring in professional exterminators or to fumigate large areas without affecting passengers.

How Hantavirus Infection Actually Happens

Hantavirus lives in the droppings, urine, and saliva of infected rodents. When these materials dry out, they turn to dust. If a person breathes in that dust, the virus can enter their lungs and cause infection. The virus can also enter through cuts or scrapes on the skin if a person touches contaminated material and then touches their face or mouth.

On the Westerdam, passengers likely did not come into direct contact with live rodents. Instead, they probably walked through or worked in an area where rodent droppings had accumulated and dried. Cleaning crew members are at highest risk because they disturb dust and debris when sweeping or wiping down surfaces.

The incubation period — the time between exposure and the first symptoms — is usually two to four weeks. This means a passenger could have been exposed while the ship was at sea, but not felt sick until after returning home. This delay made it harder to trace exactly where on the ship the exposure occurred.

Symptoms and Severity of Hantavirus

Hantavirus causes a disease called hantavirus pulmonary syndrome (HPS). Early symptoms include fever, muscle aches, fatigue, and headache — similar to the flu. After three to seven days, the illness progresses to coughing, shortness of breath, and fluid in the lungs. In severe cases, the lungs fill with fluid and the patient needs a ventilator to breathe.

About one-third of people who develop HPS die from the infection, even with hospital care. There is no cure for hantavirus; treatment focuses on supporting the patient's breathing and organ function while their immune system fights the virus. Early hospitalization and oxygen therapy improve survival rates.

Of the four Westerdam passengers who tested positive, the CDC did not release details about their outcomes. Some people infected with hantavirus have mild cases and recover, while others develop severe respiratory failure.

How Cruise Lines Respond to Rodent Problems

After the Westerdam cases became public, cruise lines increased their rodent control efforts. The industry standard now includes more frequent inspections of storage areas, engine rooms, and other spaces where rodents hide. Cruise lines also seal gaps in the hull, use snap traps and electronic traps in high-risk areas, and work with port authorities to reduce rodent activity before ships dock.

However, cruise lines do not publicly disclose which ships have had rodent infestations or how often they find rodents. This information is not required to be reported to passengers or to regulatory agencies in the United States. The CDC monitors disease outbreaks on ships, but it does not conduct routine inspections of cruise vessels for pest control.

Passengers have no way to know whether a ship has a rodent problem before boarding. The best protection is to avoid touching surfaces in storage areas, engine rooms, or other crew-only spaces, and to report any signs of rodent activity (droppings, gnaw marks, or live rodents) to crew members when ready.

Other Diseases Linked to Cruise Ship Rodents

Hantavirus is not the only illness spread by rodents on ships. Rodents also carry leptospirosis, a bacterial infection spread through their urine. They can contaminate food storage areas with salmonella and other bacteria. Rodent feces can also trigger allergic reactions and asthma in sensitive people.

Cruise ships have also reported outbreaks of norovirus and other gastrointestinal illnesses, though these are usually spread person-to-person rather than from rodents. The combination of close quarters, shared food service, and high passenger turnover makes cruise ships vulnerable to many types of disease outbreaks.

What to Do If You Were on an Affected Ship

If you were a passenger or crew member on a cruise ship and later developed fever, muscle aches, cough, or shortness of breath, tell your doctor that you were on a ship and when you traveled. Hantavirus is rare, so doctors may not think of it when ready. Mentioning your cruise travel helps them consider the diagnosis.

Hantavirus is diagnosed with a blood test that looks for antibodies to the virus. If you think you may have been exposed, seek medical care as soon as symptoms appear. Early hospitalization improves outcomes. You do not need to quarantine or isolate from others — hantavirus does not spread person-to-person.

If you were on the Westerdam or another ship that had a confirmed hantavirus case, the cruise line or health department may contact you directly. You can also contact your local health department to report your travel and ask whether you should be monitored.

Frequently Asked Questions

Can you catch hantavirus from another person on a cruise ship?

No. Hantavirus does not spread from person to person. You can only catch it from contact with infected rodent droppings, urine, or saliva. Even if someone on your ship had hantavirus, you could not catch it from them through normal contact, sharing food, or breathing the same air.

Is it safe to cruise after the Westerdam outbreak?

Hantavirus on cruise ships is extremely rare. The Westerdam case was the first widely reported outbreak on a cruise vessel in the United States. Cruise lines have increased pest control measures since then. Your risk of hantavirus exposure on a cruise is very low, though rodents can live on any ship that carries food and cargo.

How long does hantavirus stay alive on surfaces?

Hantavirus can remain infectious in dried rodent droppings for several days to weeks, depending on temperature and humidity. On a warm, dry cruise ship, the virus may survive longer than in cooler environments. This is why regular cleaning and disinfection of storage areas are important.

What should I do if I see rodent droppings on a cruise ship?

Report it to a crew member or the ship's medical staff when ready. Do not touch the droppings or try to clean them yourself. Wear a mask and gloves if you must be in the area. The ship's crew should clean and disinfect the space with appropriate protective equipment.

Can you get hantavirus from cruise ship food?

It is unlikely. Hantavirus is destroyed by cooking at normal food temperatures. However, if rodents contaminate food storage areas, they could theoretically contaminate food before it is cooked. This is why pest control in food storage areas is critical on ships.