Thinking of your holidays this bank holiday Monday? Are you one of the many people attracted by a cruise holiday? Maybe you fancy lazing on deck as the azure seas slip effortlessly by, while you look forward to good food, great entertainment and the chance to visit several countries in one holiday?
If so, you are one of an estimated 10 million people who will travel on cruise ships this year. While not wishing to dampen your enthusiasm for a holiday afloat, the World Health Organisation (WHO) recently published a review of more than 100 disease outbreaks associated with ships since 1970.
Not all of these were cruise liners, of course, with a growing cargo shipping industry and the world's navies contributing to the statistics as well.
The main diseases associated with ships are gastroentestinal disease and legionnaires' disease.
When gastroenteritis hits a ship's crew and passengers, the culprit can either be viral or bacterial. Salmonella, E coli, hepatitis A and giardia are just some of the bugs which have been found on board cruise ships. The commonest culprit is the Norwalk-like virus (NLV) which is similar to the winter vomiting bug which gripped this country recently.
NLV is extremely infectious. In one outbreak on a cruise ship in 1998, more than 80 per cent of the 841 passengers were affected by vomiting and diarrhoea.
Almost certainly introduced on board by food or contaminated water, NLV spreads rapidly from person to person. Water is a precious resource on board ship and storage tanks can become contaminated. Sometimes the cause is inadequate disinfection of water; in other outbreaks the drinking water becomes contaminated by sewage from the ship.
WHO also reported more than 50 incidents of legionnaires' disease, involving more than 200 people during the past 30 years. Legionnaires', which can cause a potentially fatal form of pneumonia, got its name when a serious outbreak of pneumonia hit delegates attending a three-day American Legion convention in Philadelphia in July 1976. Within a few days of the convention's end 29 legionnaires were dead and 180 had pneumonia.
Following intensive laboratory investigations, bacteria was isolated from both the victims and a water system in the hotel and given the name Legionella pneumophila. A group of bacteria commonly found in low harmless numbers in water, legionnellae can multiply to high levels in stagnant water. When such water reaches temperatures of between 20 centigrade and 45 centigrade, the bacteria really flourish. Although they are not a risk at low temperature, they can remain dormant and then multiply when temperatures reach a suitable level. Even the chlorination of water supplies does not guarantee elimination of legionnellae.
Almost 30 years after the first outbreak was detected, we now know that the bug is found in hot and cold water systems, cooling towers of air-conditioning units, respiratory therapy equipment, spas, Jacuzzis and thermal springs and even in the humidifiers used in food display cabinets.
The common denominator in all of these sources is the presence of water at high temperature and the potential to form aerosols [tiny droplets of water]. Legionnaires' disease is usually contracted by inhaling these aerosols into the respiratory tract.
Aspiration of contaminated water is a rare cause of infection; person to person transmission has never been proven.
Legionnaires' can be a nasty disease, particularly in the elderly, those who are immuno-compromised and for heavy smokers. Symptoms include fever, headache, abdominal pain, diarrhoea, and a non-productive cough. When severe pneumonia results, it carries a significant risk of death in vulnerable people.
Once a diagnosis is confirmed, then treatment with an antibiotic from the erythromycin group is effective. Ships' drinking water and air conditioning systems have been contaminated with Legionella pneumophilia. In one outbreak on a single cruise ship in 1994, 50 passengers were affected on nine different cruises and one passenger died. The outbreak was eventually traced to a whirlpool spa on the ship.
NOW that there is a greater awareness of the disease, preventative environmental health management is practised by cruise-ship companies. WHO will soon issue a revised guide to ship sanitation, which will emphasise good practice in this and other areas.
For those of you planning a cruise this year, as long as you choose a reputable company to travel with, you should not be taking any undue risk with your health.
Meanwhile, all travellers may be interested in a new WHO website which it claims "sets the gold standard for travel care". It can be accessed at www.who.int/ith/
Medical correspondent honooured
Dr Muiris Houston, Medical Correspondent of The Irish Times, will be conferred with a fellowship of the Royal College of General Practitioners in Birmingham on April 13th, in recognition of his outstanding contribution to general practice.
The award particularly commends his writing in The Irish Times which has "provided both accurate and balanced information on medical matters" and recognises his key role as a medical journalist in the Republic.
E-mail Dr Muiris Houston at mhouston@irish-times.ie or leave a message at 01-6707711 ext 8511. He regrets he cannot reply to individual medical problems