Cruise ships pose risk for ‘amplified,’ ‘scattered’ COVID-19 community spread, CDC official says

Cruise ships’ close-contact environments increase the risk of spreading infectious diseases as shown by multiple COVID-19 outbreaks on ships this year. The risk of spreading disease doesn’t stop when passengers disembark. 

Last week, the Centers for Disease Control and Prevention announced it suspended sailings through the end of September, and the agency shared some soberingdata about COVID-19 outbreaks on cruise ships.

The CDC revealed the breadth of contact tracing done after about 11,000 passengers and crew members left ships that experienced outbreaks. The CDC reported that the legwork required “countless hours” of work by public health officials – even more than flight contact investigations. The report noted the CDC expended an estimated 38,000 person-hours on the COVID-19 cruise ship response since March 14, though it’s unclear how many of those were devoted to contact tracing.

The results confirmed port officials’ concernsthat cruise ships pose a danger to the shoreside public when it comes to community spread of COVID-19 because of the nature of cruisers’ journeys: coming from across the globe to spend time in a close-contact environment, then dispersing and putting people in cruisers’ paths at risk. 

The CDC report revealed that from March 1 to July 10,  2,973 cases of COVID-19 or “COVID-like” illnesses emerged on cruise ships, and there were 34 deaths. During that period, there were 99 outbreaks on 123 cruise ships, meaning that 80% of U.S. jurisdiction ships were affected. Nine of those cruise ships are still dealing with coronavirus outbreaks on board.

Those numbers don’t include the Diamond Princess,  where a coronavirus outbreak in February infected more than 700 people and killed at least nine (though Johns Hopkins data says the death count was 13). The ship’s captain was the last person to depart the ship March 1 after some passengers were kept on board for a two-week quarantine, allowing the virus to continue to spread on board while others were evacuated to shoreside quarantines.

In mid-February, some of those passengers, including some who were infected after disembarkation, were evacuated on charter flights to the USA, where they were quarantined for an additional two weeks on military bases or placed under American medical care.

Unlike the Americans who had been on Princess Cruises’ Diamond Princess and Grand Princess, not all passengers on ships with COVID-19 outbreaks were subject to mandatory quarantine in a government facility, which meant the onus was on them to self-isolate after returning home.Others learned after disembarkation that fellow passengers had been diagnosed with the virus, meaning they may have unwittingly exposed anyone they encountered while traveling home.

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“Before the ‘no-sail order’ in mid-March, passengers traveled back to their homes on their own – both domestically and internationally,” Caitlin Shockey, spokesperson for the CDC, told USA TODAY, noting that the Diamond Princess and the Grand Princess, which disembarked in Oakland, California, in early March, were the only ships that were given quarantine orders for after disembarkation.

Both of those ships’ passengers had disembarked and entered quarantine by March 14, when the CDC issued its original order. After the order, some other ships with outbreaks on board allowed passengers to travel home directly instead of quarantining onshore.

When Holland America’s MS Zaandam arrived in Fort Lauderdale, Florida, in early April after a weekslong saga during which 250 passengers and crew presented flu-like symptoms and four passengers died, the majority of its asymptomatic passengers were allowed to disembark and travel home after a health screening without official quarantine orders.

Why are cruise ships so problematic when it comes to COVID-19?

Symptoms of COVID-19 can take two days to two weeks to manifest, according to the CDC. Some carriers don’t ever become symptomatic but can spread the virus. It continues to spread even after passengers leave a densely packed ship and head for the airport, where they catch commercial flights to all corners of the globe.

According to a study published in the Journal of Travel Medicine, the transmission rate of coronavirus on the Diamond Princess was four times higher than the transmission rate in Wuhan,China,which was the center of the outbreak at the time. Before quarantining, the 3,711 passengers and crew spent their time on the 952-foot ship eating, playing and sleeping in close proximity to one another as they would on most cruise ships.

“The cruise ship conditions clearly amplified an already highly transmissible disease,” the study says.

Though the study found that precautions such as isolationhelpedto reduce the transmission rate on board, preventing more than 2,000 additional cases on the Diamond Princess, it saysevacuating the ship sooner could have stopped the spread more quickly and resulted in fewer cases.

The infectious disease risk of cruising is a multipronged issue, just as cruises are a multipronged journey, said Dr. Martin Cetron, director for the Division of Global Migration and Quarantine for the CDC.

Cruisers start their journey before embarkation. By the time they board, they’ve potentially been in buses, trains, planes, airports and hotels and come into contact with people in different communities, which creates issues if parties on either side are infected.

They typically spend a week or longer in an environment with even greater chances for spread, especially if it takes a while to become aware that anyone is infected. That can lead to a delay in deployingsafety measures such as disinfection, isolation and contact tracing, potentially allowing more people to become infected.

Passengers may leave the ship during port calls, where they come into contact with communities. In doing so, they endanger the health of local populations and other passengers.

Once the cruise is over, they leave the ship and potentially take the virus back to their communities and any others they visit in transit.

“Now the virus is amplified … and scattered,” Cetron said. “It’s quite clear this is a formula for accelerated introduction, transmission and then accelerated spread.”

Even if the measure of the full impact of transmission was limited to the onboard spread, it would still be a “major problem,” he noted.

It’s extremely hard to measure the effect cruises had on the community spread, Cetron said. 

“What you see in our reported case numbers is just the tip of the iceberg,” he warned.

COVID-19’s highly contagious nature makes the situation more dire 

“This is a virus unlike many of the past viruses we have dealt with,” Cetron said.

By way of comparison, people infected with viruses such as Ebola or SARS become more contagious as they become sicker. People with COVID-19 are contagious before they are even aware they are infected, Cetron said. The CDC estimated that 40% of people who have coronavirus remain asymptomatic, leaving them unaware they could infect others.

In June, industry leader Cruise Lines International Association issued a voluntary cruising suspension through Sept. 15, and told USA TODAY that the organization, which represents the majority of oceangoing cruise ships, and its members aligned themselves with the CDC’s order issued last week – leaving their ships out of commission until October. 

Bari Golin-Blaugrund, senior director of strategic communications for the trade group, told USA TODAY that since more information has emerged about the pandemic, member lines are looking to address the problem.

“CLIA oceangoing cruise line members are sparing no resource to identify enhanced health and safety measures to adapt to the current environment and reduce the risk of COVID-19 while still providing for world-class vacation experiences,” she said. 

Even if the spread were limited on ships as it is in other high-risk settings such as meatpacking plants and nursing homes, cruising would still require action, according to Cetron.

“[It’s a] high-risk environment that needs an aggressive measure to try to control the consequences,” Cetron said. 

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