What is legionnaires’ disease? Norwegian Encore passengers diagnosed with rare illness after cruising last year

Two passengers were diagnosed with Legionnaires’ disease after traveling aboard the Norwegian Encore in December 2025, according to a letter from Norwegian Cruise Line (NCL) obtained by Cruise Hive. The cruise line has not disclosed whether the passengers were on the same sailing or which specific sailing or sailings were affected.

In the February 12 letter addressed to Norwegian Encore guests and seen by the outlet, NCL said it is working with the Centers for Disease Control and Prevention (CDC) “to investigate two cases of Legionnaires’ disease in two passengers” who traveled on the ship in December 2025.

“Legionnaires’ disease is a serious type of pneumonia caused by Legionella bacteria,” the letter states. “People can become ill when they breathe in tiny water droplets containing the bacteria.” The letter further explains that the disease is not spread from person to person. Instead, exposure can occur when droplets “occasionally form from fixtures like hot tubs, showers, bathtubs with jets, decorative fountains and misters.”


The disclosure comes amid broader concerns about Legionnaires’ disease on cruise ships. In October 2024, the CDC released a report on an unrelated investigation involving 12 cases of Legionnaires’ disease among travelers on two cruise ships between November 2022 and June 2024. The study found that private balcony hot tubs “were the likely source of exposure in two outbreaks,” noting that these facilities are “subject to less stringent operating requirements than are public hot tubs.”

Here is everything you need to know about the rare Legionnaires’ disease.

What is Legionnaires’ disease?

Legionnaires’ disease is a type of pneumonia caused by breathing in Legionella bacteria. According to the Cleveland Clinic, the infection can affect the lungs, brain, and gastrointestinal tract. Many patients become severely ill and require hospital treatment, and some may experience long-term health problems even after recovery.

Symptoms typically develop two to 14 days after exposure, though they can appear later. As per the CDC, symptoms resemble other forms of pneumonia and include cough, fever, headaches, muscle aches, and shortness of breath. Other symptoms, such as confusion, diarrhea, or nausea, can also occur.

How rare is Legionnaires’ disease?

Legionnaires’ disease is relatively uncommon. As per the Cleveland Clinic, around 10,000 people in the United States are diagnosed with the illness each year.

How do people get infected?

People can contract Legionnaires’ disease by breathing in mist, or aerosolized water, contaminated with Legionella bacteria. Water can also accidentally enter the lungs through aspiration, such as when it goes “down the wrong pipe,” the Cleveland Clinic explains. Potential sources include hot tubs, showerheads, faucets, humidifiers, decorative water features like fountains, heating and cooling systems in large buildings, intubation during surgery, and even soil.

The Cleveland Clinic notes that swallowing contaminated water does not cause infection and that the disease is not contagious. Outbreaks have previously been linked to hotels, hospitals, long-term care facilities, and cruise ships. The CDC has also warned that Legionella can grow in windshield wiper fluid tanks if filled with water, recommending the use of “genuine windshield cleaner fluid” to prevent bacterial growth.

Legionnaires’ disease treatment

Legionnaires’ disease requires treatment with specific antibiotics, and most cases can be treated successfully if identified early. Healthy individuals often recover but typically need hospital care during the illness, according to public health guidance by the CDC.