Published Date: 2002-12-07 23:50:00
Subject: PRO/EDR> Norwalk-like virus, cruise ship - USA (FL) (12)
Archive Number: 20021207.6000
NORWALK-LIKE VIRUS, CRUISE SHIP - USA (FL) (12)
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Date: Fri 6 Dec 2002
From: ProMED-mail <promed@promedmail.org>
Source: New York Times online, Fri 6 Dec 2002 [edited]
<http://www.nytimes.com/2002/12/06/national/06CRUI.html?pagewanted=all&position=top>
Virus rattles cruise industry and health officials
--------------------------------------------------
Reports from the Caribbean cruise ship Oceana began arriving at the Centers
for Disease Control and Prevention (CDC) late on Tuesday. By Wednesday
night, the picture was disturbingly familiar: 117 on board were violently
ill with vomiting and diarrhea, the same symptoms that had laid passengers
low on 3 other ships in the last 2 months. A common and highly contagious
infection caused by a Norwalk-like virus has been confirmed on 2 ships and
is suspected on another 2. Since October 2002, the virus has sickened at
least 900 passengers and crew members on cruise ships.
The outbreaks are creating a mystery for federal health officials and are
rattling passengers and cruise company executives. Norwalk-like viruses
have hit ships before, but health officials said they did not know why the
recent outbreaks were occurring, and they said the recent burst of cases
appeared to be an increase over previous years. The nature of the viruses
-- they are common, hardy, highly contagious, and hard to track -- raises
the possibility that periodic outbreaks on ships may be inevitable, one
more risk that the traveling public must factor into the calculation of
whether to book tickets or stay home.
The tight quarters of a ship provide ideal conditions for contagious agents
such as Norwalk-like viruses to multiply. Rapid turnaround times -- often
just hours between one cruise and the next -- can make it difficult to
eliminate stubborn organisms. Sick or recovering passengers, loath to spend
their vacations in their cabins, may infect others, as may crew members who
work while ill. Dr Megan Murray, a Harvard epidemiologist who was a
consultant for the Holland America Line on disinfecting its cruise ship
Amsterdam, which had outbreaks on 4 consecutive voyages, said that illness
on ships may reflect the many outbreaks now occurring on land. Scientists
said the recent patterns of shipboard cases indicated that the illness was
coming not from food or water on the ship, but from infected passengers or
crew bringing the virus onto ships. Cruise executives say there has been no
big drop in bookings. But in the last 5 days the stock prices of several
major cruise companies have fallen sharply. The Amsterdam and the Disney
Magic each canceled a cruise recently so the ships could be scrubbed,
steamed, and disinfected with bleach and other chemicals. But there is no
reliable test to detect the virus on surfaces, so the only way to tell
whether a ship has been disinfected is to send it out again and see whether
anyone gets sick.
At least 23 different strains [that is, species; the genus "Norwalk-like
viruses" has been renamed _Norovirus_. - Mod.CP] of Norwalk-like viruses
can infect people. Most adults have been exposed to at least one, Dr Murray
said. The name comes from Norwalk, Ohio, where the first virus of this type
to be identified caused an outbreak of gastrointestinal illness in 1968.
The virus was identified later from stored stool samples. The viruses are
spread by what scientists call the fecal-oral route. This can occur when
infected people fail to wash their hands after using the toilet and then
touch other people, common surfaces, or food. In some outbreaks, though
apparently not the recent ones on ships, people have caught Norwalk-like
viruses from eating raw or undercooked shellfish taken from sewage-laden
waters. They can then pass the infection to others. Cruise passengers have
been advised that they can reduce the risk of infection by washing their
hands frequently and keeping their hands out of their mouths to avoid
ingesting viruses they may have picked up from touching doorknobs and railings.
Handwashing does not protect against incidents of "public vomiting", which
have occurred on ships because the illness can cause sudden nausea, Dave
Forney, head of the vessel sanitation program at the CDC, said. It takes
only a small dose of the virus, 100 particles or even fewer, to make a
person sick, according to studies of people who volunteered to become
infected by drinking a stool filtrate. The incubation period is usually a
day or 2, and the illness lasts a few days, causing nausea, vomiting,
stomach cramps, diarrhea, and sometimes fever and headache. People become
immune after being infected, but the immunity probably does not last more
than a few months, stated Dr Widdowson, an epidemiologist at CDC. Still,
such people appear to eliminate the virus from their bodies, and do not
become carriers. Immunity to one strain does not protect against others.
On land, the vast majority of people with gastrointestinal illness like
that caused by Norwalk viruses recover on their own and do not see a
doctor. "We have several outbreaks a month of Norwalk-like virus
infection," he said, adding that, since January 2002, CDC had confirmed 37
outbreaks in the United States, including those on ships. The number is
typical, he said.
The cruise-ship cases may stand out because they are more likely than the
ones that occur on land to be reported to health officials. CDC requires
that medical officers on ships report cases of gastrointestinal illness,
and it may investigate and conduct diagnostic tests if the infection hits
at least 2 per cent of the passengers.
In July 2002, a Norwalk-like virus outbreak felled 388 passengers on the
Ryndam on 2 consecutive cruises to Alaska. The ship was taken out of
service to be disinfected. Then in October, 193 passengers on the Amsterdam
became sick on a cruise through the Panama Canal that had begun in Seattle.
After 3 more Amsterdam cruises out of Port Everglades brought down another
261 passengers, the shipping company decided to cancel a cruise in order to
swab and steam-clean the Amsterdam (Both the Amsterdam and the Ryndam are
owned by the Holland America Line, which is owned by the Carnival
Corporation). At about the same time, the Disney Cruise Line began
disinfecting its 2500 passenger Disney Magic after 483 passengers on 2
cruises became ill. On 4 Dec 2002, CDC reported that 114 passengers and 3
crew members were ill on the Oceana. The Oceana, a new ship, was on only
its third cruise. Mr Forney said all the ship's passengers were from the
United Kingdom, and that all the sick ones had flown to Florida on the same
charter flight. Some, he added, got sick during their first day on the ship.
When a ship carrying 2000 passengers finishes a cruise, crews may have only
3-4 hours -- 15 minutes per room -- to clean the ship before the next round
of passengers board. Industry executives say that is enough time, because
ships are cleaned continuously while they are sailing, with 30 to 40 people
constantly cleaning. But executives also say that given the outbreaks, the
ships are being cleaned more frequently, and with stronger chemicals.
"Every hour, we clean the handrails, elevator buttons, counters, flat
surfaces, exercise equipment," said Manny Rivas, a manager of public health
matters at Royal Caribbean Cruise Lines. But Dr Murray said that scientists
are not sure which disinfectants kill Norwalk-like viruses, and that more
research is needed to find out. She said that steam-cleaning carpets and
upholstery is thought to do the job, but only if the carpeting can be
heated up to 160 degrees Fahrenheit [71 degrees C], and not all equipment
can do that. So far, the best way to disinfect a ship seems to be to take
it out of service for intensive cleaning. The combination of scrubbing and
keeping people away seems to break the cycle of transmission, Dr. Murray said.
[byline: Denise Grady]
--
ProMED-mail
<promed@promedmail.org>
[There have been discordant statements about duration of immunity in
relation to infection with Norwalk-like viruses, which require
clarification. Information on the precise identity of the strains/species
of Norwalk-like viruses involved in these outbreaks is entirely lacking.
Until that information becomes available, it will be difficult to interpret
properly the epidemiology of these outbreaks. - Mod.CP]
See Also
Norwalk-like virus, cruise ship - USA (FL) (11) 20021205.5973Norwalk-like virus, cruise ship - USA (FL) (10) 20021204.5962
Norwalk-like virus, cruise ship - USA (FL) (09) 20021203.5955
Norwalk-like virus, cruise ship - USA (FL) (08) 20021202.5949
Norwalk-like virus, cruise ship - USA (FL) (07) 20021129.5917
Norwalk-like virus, cruise ship - USA (FL) (06) 20021128.5912
Norwalk-like virus, cruise ship - USA (FL) (05) 20021122.5868
Norwalk-like virus, cruise ship - USA (FL) (04) 20021120.5854
Norwalk-like virus, cruise ship - USA (FL) (03) 20021113.5791
Norwalk-like virus, cruise ship - USA (FL) (02) 20021112.5783
Norwalk-like virus, cruise ship - USA (Florida) 20021026.5642
Norwalk-like virus, cruise ship - USA (Alaska) (04) 20020803.4932
Norwalk-like virus, cruise ship - USA (Alaska) (03) 20020726.4870
Norwalk-like virus, cruise ship - USA (Alaska) (02) 20020610.4462
Norwalk-like virus, cruise ship - USA (Alaska) 20020607.4432
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