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Clean Sailing: The War on Norovirus


10 May 2011


Infection rates have hit a ten-year low on US cruise ships, thanks to years of fast-paced updates to hygiene practices. CLIA's Budd Darr and RCCL's Dr Art Diskin discuss the war on norovirus, the importance of reporting outbreaks, and the new Vessel Sanitation Programme.


In brochures, cruise liners are portrayed as floating super-hotels, but for medics onboard, they're potential breeding grounds for gastro-intestinal illness. The US cruise industry has waged a long battle against infections on its ships and in early 2011 the Centre for Disease Control and Prevention (CDC) revealed that rates of gastrointestinal outbreaks on cruise ships had hit a ten-year low.

While cruise volumes were rising by an average of 600,000 passengers a year, according to the Cruise Line International Association (CLIA), operators adopted cutting-edge methods that resulted in just 13 outbreaks on ships leaving US ports in 2009.

VSP influence

The US cruise industry can attribute much of its success to the support of the CDC's vessel sanitation programme (VSP). The programme was established in the early 1970s and has since gained international recognition for its service to public health on cruise ships and chartered voyages.

Any ship carrying more than 12 passengers must pass an assessment by the CDC before it embarks, with the ship's water supply, spas and pools, food, employee hygiene and health training, and the overall state of the ship all measured according to criteria set out in the VSP operations manual.

The CDC plans to publish the next editions of the operations manual and construction guidelines in 2011. As a CDC partner, CLIA is obliged to report outbreaks in detail and Budd Darr, CLIA's director of environment and health programmes, claims that this exchange is vital in the fight against infections at sea.

"We and the CDC can learn a lot from surveillance data," he says. "We need to be diligent. We can't go backwards from the efforts we've made so far."

"Cruise operators adopted cutting-edge methods that resulted in just 13 outbreaks on ships leaving US ports in 2009."

At the same time, Darr says that the VSP is a voluntary programme, and for many of his members it represents the minimum standard they strive for.

"Our members score 97 out of 100 for hygiene, the pass rate being 85," he says.

This demonstrable lead shows how advanced the industry is on a world scale. He also points out that noroviruses are statistically uncommon on cruise ships. Of the 21 million cases reported in the US last year, only 1,759 involved cruise passengers. Another 5,000 experienced norovirus, but were below the outbreak criteria. However, a small number of outbreaks continue to blight cruise passengers and Darr argues that it is in the industry's own interests to manage and report them.

"The industry represents a very high level of effort and standards, and compares extremely favourably not only with other industry standards, but also shore-based clinical practices such as local public health."

Nonetheless, he says, the health and safety of passengers is important to the industry and its practices regarding prevention, response and surveillance will continue to develop whatever the rates of infection.

"As long as there's disease, there's room to improve," adds Darr.

Dr Art Diskin, chief medical officer at Royal Caribbean Cruise Lines (RCCL), echoed Darr's praise for the CDC's analysis of and response to trends. He highlighted one example of its observations, a new and disturbing change in the pattern of outbreaks. "A long voyage that reports sickness among 3% of passengers might not be cause for comment, but the virus has changed in the last year. It used to be that on the second, third and fourth days you'd find numbers rising from ten to 50 cases. But we're seeing an increase in fast, explosive outbreaks now that go from 0-150 in 24 hours."

The CDC notes these outbreaks and, if a pattern emerges, conducts onboard investigations. Afterwards, it suggests changes to policies and procedures. For example, if two ships use the same pier and one has an outbreak in progress, the CDC will advise the other how it can protect its passengers. Diskin anticipates an outbreak on every voyage and says that, no matter how RCCL staff approach the problem, they can't avoid outbreaks all year round.

Passengers are screened before joining a cruise, kept under medical surveillance during their holiday and are informed of the free medical treatment available for gastrointestinal illnesses. RCCL uses the six-in-six rule – if six cases are presented in six hours sanitation procedures increase from level 1 to 2, also known as Code Red.

"Until guests are perfectly educated on the tenacity of the norovirus, chemical surfactants are the cruise ship's greatest weapon against the disease."

The cruise line is careful to manage the risk of carrying viruses from one cruise to another. After outbreaks, staff disinfect the ships thoroughly. Embarking and disembarking passengers are kept completely separate, luggage and vehicles going to and from the ship are sanitised, and transfer passengers are screened before embarking on another cruise.

Power of passenger hygiene

Controlling infection risk is vital, but Diskin attributes much of the success of the past decade to better public hygiene.

"Even if people don't tell you they're ill they isolate themselves," he says. "More people follow the hand-washing advice than before and the public's much better educated on preventing the spread of disease."

Nonetheless, guests can also pose the greatest threat to one another's health. The most visible way the norovirus spreads is through public vomiting but, within 24 hours of the last episode, it is no longer airborne. However, the virus is much more tenacious than it seems – it can be shed from the body through the faeces for several weeks after symptoms disappear.

Passengers can be as stubborn as the disease itself if they worry that honesty in screening surveys, days of quarantine or time-consuming hand hygiene will get in the way of their holiday. So, until guests are perfectly educated on the tenacity of the norovirus, chemical surfactants are the cruise ship's greatest weapon against the disease.

Cruise's irresistible challenge

The Holy Grail for cruise ships is to find cleaning agents that can kill a virus quickly without being too toxic or corrosive. Chemicals should also be easy to use and transport, and in concentrated solutions if possible. For the cleaning industry, the cruise challenge has proved irresistible and has produced strong results.

"Sanitation against norovirus has changed in the last ten years," says Diskin. "We used quaternary ammonium salts with a best contact time of ten minutes. Now we've got cleaners with a five-minute kill-time."

Notably, Diskin's employer reported just one outbreak last year. As the CDC prepares to deliver an update of the VSP's construction and operations materials in late spring, the world-leading cruise industry will be rolling up its sleeves for another season of germ warfare.