New protocols have seen Norovirus outbreaks drop

One apparent result of the measures cruise lines have taken against COVID-19: Outbreaks of gastrointestinal illness have been much lower than in the years before the pandemic.

So far this year, cruise lines have reported two outbreaks of vomiting and diarrhea to the US Centers for Disease Control and Prevention that affected three percent or more of passengers or crew. That’s part of the outbreak threshold that determines whether the agency releases episodes to the public. Ships must have a foreign itinerary with US ports and must carry at least 100 people.

The two outbreaks, which affected a total of 113 people, occurred on a Carnival Cruise Line ship in late May and on a Seabourn luxury voyage from late April through May. Norovirus was the cause of the Carnival’s illnesses, the CDC said on its site dedicated to updates on gastrointestinal illnesses on cruise ships; Seabourn’s cause was unknown.

Last year, when cruise lines began sailing again after a hiatus of more than a year, only one outbreak was reported. That one, caused by Vibrio and E. coli bacteria, struck 120 people on a Viking Ocean ship. Operators did not report any cases in 2020; the industry voluntarily closed in March of that year.

Three outbreaks over the course of more than a year is much lower than pre-pandemic figures. In an email, the CDC said the decrease in the number of acute gastroenteritis outbreaks “could likely be attributed” to a combination of fewer passengers on ships during that time and “non-pharmaceutical interventions used by cruise ships to mitigate transmission of COVID-19, such as increased cleaning and sanitizing, an increase in the number of hand sanitizer stations, crew-served buffets, and physical distancing.”

Norovirus cases on land are also lower than normal. According to the CDC, the number of outbreaks reported by states during the 2021-2022 seasonal year (August through July) is lower than the range reported during the same period over the previous eight years.

CDC’s Vessel Sanitation Program has worked with industry to control gastrointestinal illnesses since 1975, after “an excessive number” of outbreaks. While stomach illness incidence rates on cruise ships dropped between 2006 and 2019, according to the CDC, pre-pandemic numbers were closer to 10 or 11 outbreaks per year. Between 2017 and 2019, cruise lines reported a total of 32 outbreaks that sickened 3,359 people. Norovirus, which the CDC says “can spread rapidly in closed and semi-closed settings such as cruise ships,” was found to be the cause in 22 of those episodes.

That’s a small fraction of the number of cruise passengers during those years: More than 13.7 million cruise passengers took cruises from US ports in 2019, according to the Cruise Lines International Association.

William Schaffner, a professor of infectious diseases at Vanderbilt University School of Medicine in Nashville, said the reduced number of cruise ships as the industry restarted and the lower concentration of passengers, at least on many lines, would likely be factors in fewer outbreaks. But he said precautions against COVID-19 are also “undoubtedly helpful” in combating the spread of norovirus.

“The more rigorous we are with all these hygienic measures, they spread to other infectious agents,” he said.

Norovirus, he said, is “extraordinarily” contagious. Schaffner praised cruise lines for their sanitizing practices even before the coronavirus emerged.

“Before that happened, the cruise industry, under the guidance of the CDC, put in a lot of infection control activities that they really put in place rigorously,” he said.

Cruise lines have touted enhanced cleaning and sanitation protocols since the pandemic began. Royal Caribbean International, for example, says on its website that while hand sanitizing stations have always been on board, the line has increased the number by 75 percent.

“And we’re putting them anywhere you’re most likely to use them, near elevators and at exits and entrances everywhere, plus anywhere on board that doesn’t have handwashing stations or sinks in the area.” immediate,” the site says. .

The company said it had improved its cleaning protocols, noting that high-traffic areas such as elevators, stairs, escalators and walkways are cleaned every two hours, and handrails are cleaned every 20 to 30 minutes when the neighborhood is busy. .

Norwegian Cruise Line said it had implemented “enhanced comprehensive cleaning and sanitation protocols” and had a dedicated public health officer on all ships to “oversee the daily sanitation and cleaning of all public areas and accommodations.”

At least temporarily, some cruise lines have ditched self-service buffets in favor of staff serving passengers at food stations, though the old style has largely made a comeback, according to cruise news site Cruise Critic.

The CDC says that norovirus is spread by direct contact or by sharing food or utensils with someone who is infected. Outbreaks can also result from food, water, or surfaces that have been contaminated. Common settings include health care facilities, restaurants, schools or daycare centers, and cruise ships, the agency says, though it notes that ships account for just one percent of all norovirus outbreaks.

The virus can last on surfaces for days to weeks, according to the CDC.

“Norovirus control can be especially difficult on cruise ships due to close living quarters, shared dining rooms, and rapid passenger turnover,” the CDC says on its website. “When the ship docks, norovirus can be carried on board in contaminated food or water or by passengers who became infected while ashore.”

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