A crew member fell ill with measles, prompting fears of an outbreak on a cruise ship owned by the Church of Scientology -- and it's the latest reminder that infectious diseases can spread among hundreds of people.
The quarantine at the Freewinds might be unique but scores of travelers have gotten sick when sailing at sea in recent years.
"When you have a lot people in a closed environment, whether it's a nursing home or an institution like a school or a cruise ship, it's more like an incubator because people are in closer proximity and viruses can end up in the air and on surfaces that people touch," said Claire Panosian, a professor emeritus in the division of infectious diseases at the David Geffen School of Medicine at UCLA.
Last year, 11 cruise ships carrying hundreds of passengers to the United States reported outbreaks of rotavirus, norovirus and E. coli, according to the US Centers for Disease Control and Prevention.
While the CDC only tracks vessels carrying hundreds of people and those where 3% of passengers or crew report gastrointestinal illnesses, experts said more outbreaks might exist.
How easily can people get infected?
Earlier this year, a Royal Caribbean ship cut its itinerary short and returned to Florida when hundreds of people were sickened by a gastrointestinal illness. Initially 277 passengers and crew were reported to be ill but that number jumped to 475 people a day later.
As people sleep, eat and socialize in a tight space such as a cruise ship, viruses and bacteria can move even faster.
The most common outbreaks involve not only gastrointestinal infections but also vaccine-preventable diseases such as chickenpox and influenza.
"When you have people in a closed environment, one person with a respiratory illness can infect a lot of other people," Panosian said.
Health officials in the Caribbean island of St. Lucia quickly ordered a quarantine this week at the Freewinds with only one case of measles. A female crew member was placed in isolation inside the ship as officials feared more people could be sick.
About 300 people aboard were eating together at shared dining areas, walking the same closed hallways and sleeping in confined spaces. If an infected person coughs or sneezes, the virus can still live in the air for as long as two hours.
If someone who is not immune to the virus breathes the air or touches an infected surface, they can become infected, the CDC said.
Measles cases in the United States have surpassed the highest number on record since the disease was declared eliminated nationwide in 2000.
How can people protect themselves?
Make sure you're vaccinated and wash your hands frequently.
The CDC also recommends that travelers avoid touching their eyes and mouth, disinfect surfaces and toys with standard household products, and refrain from coming into close contact or sharing silverware with anyone who's sick.
When eating off the ship at a port, travelers should be cautious about what they eat and the water they drink. They should also take measures to prevent insect bites, "especially in malaria- or dengue-endemic areas or areas with outbreaks of vectorborne diseases, such as chikungunya and Zika," the CDC says.
And if you have to cough or sneeze, use your sleeve or a tissue -- but not your hands, the CDC says.
Travelers who think they've been exposed to measles or any other infectious disease, the agency said, should report it to the onboard medical staff and call their doctor.
For people in the midst of an outbreak who are unsure about their status or think they might be infected, public health experts recommend limiting contact that could spread the virus.
Those who suspect they are infected should delay travel until they are no longer contagious, CDC says.
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