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multidisciplinary group sponsored by the Chlorine Chemistry Council. Its mission is to promote science based practices and policies to enhance water quality and health by advising industry, health professionals, policy makers and the public.
 

Sea Sick -- Infection Outbreaks Challenge the Cruise Ship Experience

For decades, cruise ships have been a popular vacation destination for those seeking a reprieve from the wintertime blues. Over ten million people traveled on cruise ships in 2000 and that number is expected to double by 2010. But some recent vacationers have found themselves wishing they never said, "Bon Voyage."

In 2002, a wave of gastroenteritis outbreaks occurred aboard several international cruise ships, turning the sojourns of many sea-bound, sun-revelers into shortened trips they would most likely want to forget. As recently as February 2004, more than 300 Carnival Cruise Line ship passengers were stricken with the stomach malady while aboard the Celebration luxury liner while on a Valentine's cruise in Mexico. Unfortunately, such outbreaks are not a surprise to the industry. According to a 2003 World Health Organization (WHO) study, "Emerging Issues in Water and Infectious Disease," since 1970 over 100 disease outbreaks associated with cruise ships have been documented. The WHO considers this figure low, because many such illnesses go unreported.

Virus on the High Seas

Among the several illnesses and maladies that can affect a cruise ship passenger, food and water borne viral gastrointestinal illness is the most common culprit. Symptoms include nausea, vomiting, diarrhea and in some instances, severe stomach cramping. Transmitted person-to-person (meaning it can be transferred both through human contact and through contact with food, water or surfaces that are contaminated with illness-causing germs), an infectious virus has the ability to take on outbreak proportions quickly in the closed environment of a cruise ship. With the complicating factor that these viruses can remain active on objects and surfaces for periods of up to 14 days, the likelihood of human exposure to the virus is greatly increased, facilitating its spread and increasing the probability of infection outbreaks.

The most common type of virus linked to gastrointestinal illness is the Norwalk-like Virus (NLV) or norovirus, which gained notoriety from a 1968 outbreak in Norwalk, Ohio. The term norovirus was recently approved as the official name for this group of viruses. Several other names have been used for noroviruses, including, caliciviruses (from its origin in the virus family Caliciviridae) and "small round structured viruses". Noroviruses are the leading cause of gastrointestinal illness with an estimated 23 million cases a year, according to the U.S. Centers for Disease Control & Prevention (CDC).

Typically, shipboard norovirus spawns from poor sanitation conditions, including contaminated bunkered water, inadequate disinfection of potable water, potable water contaminated by sewage on ship, deficiencies in food handling, and poor food preparation and cooking methods. Significantly, there is no vaccine to prevent contracting norovirus. Antibiotics will only work to fight bacterial infection, not to treat viral outbreaks.

From July 1997 to June 2000 there were 232 outbreaks of norovirus illness reported to the CDC of which, 57% were foodborne, 16% were due to person-to-person spread, and 3% were waterborne. In 23% of outbreaks, the cause of transmission was not determined. According to the CDC common settings for outbreaks include restaurants and catered meals (36%), nursing homes (23%), schools (13%), and vacation settings or cruise ships (10%). The CDC estimates that as many as half of all food-related outbreaks of illness may be caused by norovirus. In many of these cases, food handlers experiencing a viral illness were identified as the likely carriers and transmitters of the disease.

Complicating matters, it has been discovered that norovirus is a nimble and difficult virus to control. Recent research conducted by the UK Health Protection Agency suggested that a new variant of the virus was to blame for the spate of 2002 cruise ship outbreaks. Through data collection, the Agency discovered a specific and identifiable mutation in one of its genes.

Nothing New Under the Sun

While recent events have focused media attention as never before on the public health conditions in the cruise ship industry, the story of shipboard illness is not a new tale. In an effort to prevent contamination aboard luxury cruise ships in the early 1970's, the CDC established the Vessel Sanitation Program (VSP). Under the VSP, over 140 cruise ships are subjected to unannounced, twice-yearly inspections where the ship must score 86 or above on a 100-point scale. The inspections are conducted in U.S. ports only, and are overseen by VSP environmental health officers. Inspectors focus on the ship's water supply, spas and pools, food, employee hygiene, ship cleanliness and a review of the ship environmental training programs. The VSP also monitors reports of diarrheal illness on each ship.

If an outbreak of gastrointestinal illness occurs, the VSP works with other infectious disease programs at the CDC to initiate an investigation. An outbreak is defined as having 3% or more of either passengers or crew reported with illness. Cruise vessels sailing to U.S. ports are required to notify the CDC of every case of gastrointestinal illness reported to the ships' medical staff for each cruise. This summary report must be filed 24 hours prior to arrival at a U.S. port. If the number of ill passengers or crew reaches 2% during the cruise, the vessel is required to file a special alert report informing health authorities of the abnormality. The CDC closely monitors these illness reports on a daily basis.

Back-to-Basics Is the Key to Prevention

Whether shipboard or at home, preventive steps are considered to be the best means of avoiding contracting norovirus infection or similar viral illness. By practicing sound and sensible personal hygiene, individuals can help reduce the chances of contracting the virus and spreading it. The CDC's recommended preventive measures include:

  • Frequently wash your hands (especially after toilet visits)
  • Carefully rinse fruits and vegetables
  • Thoroughly clean and disinfect contaminated surfaces with a chlorine bleach-based cleaner immediately after an episode of illness
  • Immediately remove and wash clothing or linens that may be contaminated with the virus after an episode of illness

Prevention of food-borne norovirus disease is based on safe storage and handling habits for both food and water. While noroviruses are relatively resistant to environmental conditions (they are able to survive freezing, temperatures as high as 60C, and have even been associated with illness after being steamed in shellfish), relatively simple, common sense measures can limit much of their impact. Correct handling of cold foods, frequent hand washing, and not handling food when ill are suggested as habits that may substantially reduce food-borne transmission of norovirus.

Additionally, many local and state health departments are requiring that food handlers and food preparers who have suffered recent bouts of gastroenteritis not work until 2 or 3 days after they recover from their illness. Significantly, since the virus continues to be present in human waste for as long as two to three weeks after the person feels better, strict hand washing after using the bathroom and before handling food items is considered critical to the prevention of a viral spread. Recommendations include the proviso that food handlers who have experiences illness can be given alternate duties to direct contact with consumables, such as running the cash register or hostessing.

A Recent Wave

The year 2002 was a wake up call for a world largely unfamiliar with noroviruses. There were 25 reported outbreaks of the Norwalk-like virus on cruise ships, leaving a total of 2,648 passengers ill on their vacation get-aways. Major cruise lines such as Norwegian, Royal Caribbean, Carnival, Holland America and Disney were hit 19 times by outbreaks of gastrointestinal illness, all of which were attributed to norovirus.

In October and November 2002, Holland America's Amsterdam cruise ship experienced four successive cruises in which norovirus struck members of both the crew and passengers. A total of 524 people (passengers and crew) had become ill -- roughly 25% of the ship population for the total of the four cruises. The first cruise, which ran from Oct. 1st - 22nd, had 196 passengers and a dozen crew contract the Norwalk like virus. The ship was disinfected, scrubbed and cleared to embark on its next voyage. The following cruise (Oct. 22nd - Nov. 1st) had an outbreak as well, with 41 passengers and 8 crewmembers becoming ill from Norwalk-like viral infection. The result was that Holland America was drowning in a sea of bad publicity, as the cruise line was routinely portrayed as an unhealthy breeding ground for the virus.

Prior to boarding on its Nov. 1st -11th cruise, the staff of Holland America distributed a printed notice to passengers, informing them that the previous cruise had been disinfected. Yet despite adhering to CDC's disinfection and sanitation measures, the outbreaks continued with 163 passengers and 18 crewmembers confirmed ill. It was reported that the common greeting among passengers was to rub elbows to avoid direct hand-to-hand contact.

Despite three successive cruises with an outbreak, Holland America's Amsterdam set out Nov. 11th on another cruise. Yet again an outbreak developed, with 36 people offloaded for symptoms associated with Norwalk. Finally on November 21st, the vessel was temporarily taken out of service for aggressive cleaning, isolation of affected crew and other control methods. The Amsterdam was back on the seas December 1st, reporting on a daily basis to the CDC.

An Ongoing Battle

While the cruise ship industry in total reports that it is follows strict regulations designed to prevent viral contamination and public health challenges, norovirus outbreaks have continued to occur. In December 2002, Carnival Cruise Lines suffered back-to-back outbreaks on its 7-day Caribbean cruises bound for New Orleans. That same month Royal Caribbean also reported that two of its cruise ships had Norwalk-like virus outbreaks.

The CDC reported in its 2002 year-end review that the cruise ship outbreaks of that year demonstrated just how easily norovirus is transmitted from person to person in a closed environment. According the CDC, both the event of outbreaks on consecutive cruises populated by new passenger and the resurgence of outbreaks caused by the same virus strains during previous cruises on the same ship (or on different ships of the same company), suggests that environmental contamination and infected crew members can serve as reservoirs of infection for passengers. It also offered possible explanations for the increase in infection rates, positing that the 2002 outbreaks might have reflected either an actual increase in norovirus outbreaks, or could have been attributable to improved surveillance with an electronic reporting format implemented January 1, 2001. New bio-surveillance systems and the increased application of sensitive molecular assays capture data on cases of illness reported to the ship's infirmary or to designated staff on board the ship.

Emphasizing basic food and water sanitation measures, the CDC recommended control efforts that should include thorough and prompt disinfection of ships during cruises, and isolation of ill crew members and passengers (if possible) for 72 hours after clinical recovery. Rapid implementation of control measures at the first sign of a suspected gastrointestinal outbreak is considered to be critical in preventing additional cases of illness aboard ship. Chlorine-based cleaning solutions are recommended for disinfection. When routine disinfection measures are unsuccessful in interrupting the viral spread, the CDC recommends more extensive disinfection procedures, as well implementation of a waiting period - a sustained time without passengers aboard a ship to facilitate final eradication of the virus.

With no single, easy-to-implement solution on-tap, conventional public health regimens are still considered to be the best method of halting infection outbreaks in the cruise ship industry. A back-to-basics approach that includes common sense personal hygiene routines and safe, effective disinfection practices are viewed as the best defense against a public health foe that continues to ride the waves.

   
 

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