This year more than 13.5 million people, including more than 260,000 New Zealanders and Australians, will choose to embark on an ocean cruise.
Cruise travel is booming like never before, it is a $60 billion industry, and the ships are getting bigger, the number of passengers travelling greater, the locations visited more exotic, and the range of activities and facilities ever-expanding.
Cruising is seen as a relaxing, exciting and hassle-free way to go, a Love Boat experience, offering the opportunity to visit many different places and cultures, even if only for a few hours. The numbers cruising have almost doubled in the last six years.
Fourteen new ships will be launched this year, and one, Royal Caribbean's new flagship, is an extraordinary 220,000 tonnes, with 16 decks capable of transporting 6400 passengers and 2500 crew. The newer cruise ships are "floating cities" coming in at more than 150,000 tonnes, providing an extraordinary environment of decks, lifts, casinos, shopping arcades, parks, restaurants, lounges, bars, cinemas, bingo halls and swimming pools.
As well they generate vast amounts of waste and millions of litres of polluted water. While some cruises have attracted an elderly clientele in various states of wear, more middle-aged and young adults are also travelling, as well as young children.
But just how safe is cruising? Are we more at risk on board a mega-liner than walking in downtown Auckland or Wellington?
Are passengers on "singles" cruises more at risk of sexual violence and sexually transmitted diseases than they might be at home, and given that many of the crew are drawn from the developing world, are they at greater risk of harbouring infections such as TB and hepatitis B? Evidence produced at a US Congress hearing in 2007 suggests that one is as much as 50 per cent more likely to be sexually assaulted on a cruise ship than on land. Between 1999 and 2007 sexual assaults increased 100-fold on cruise ships. Nearly 70 per cent of these assaults were carried out by crew on passengers and 10 per cent by crew on fellow workers.
There seems little doubt that the majority of these attacks go unreported. Evidence also seems to suggest that casual consensual sex on cruise ships involves at least 10 per cent of all travellers and cruise-acquired sexually transmitted diseases are probably fairly common.
Generally, medical problems aboard cruise ships largely mirror those on land in that the most common diagnosis is respiratory illness followed by sprains and superficial wounds and minor contusions. Recently, however, much attention has been focused on the increasing number of episodes of gastrointestinal illness on board cruise ships and there is evidence that the rate has increased substantially since 2001.
Since 2005 there have been more than 80 incidents of major contagious disease outbreaks on cruise ships involving more than 12,000 people. Without much doubt this understates the true situation as many would suffer relatively minor illness in silence, particularly when access to the ship's medical services are limited and expensive.
Since 2002 a wave of norovirus outbreaks has swept international cruise ships resulting in substantial epidemics and transforming the seagoing vacation of many sun-revellers into trips they would rather forget.
In some cases substantial epidemics have raged, as on two large cruise ships in 2004 and 2005, when between 30 and 41 per cent of all passengers were swept up in major epidemics of gastroenteritis. Nothing much has changed, it would seem, and in January of this year 145 Celebrity Cruise travellers and seven crew were stricken with a severe gastrointestinal infection.
Norovirus has become the most common cruise infection and is closely linked to poor hygiene and sanitation, inadequate disinfection of potable water and deficiencies in food preparation and handling. Significantly there is no specific treatment for norovirus infections.
Cruise ships, by their very nature, are perfect breeding grounds for infectious diseases. They bring together people from a wide variety of contexts and backgrounds and sequester them in a small confined space, often sharing basic facilities with common food and water supplies, providing a sympathetic environment within which respiratory and enteric infections can easily spread.
In addition, about one-third of all passengers are elderly and thus may be more susceptible to infectious disease. Crew members have also on occasions acted as reservoirs of infection, effectively transmitting infectious disease from cruise to cruise.
Overall, while it would appear that the incidence of gastrointestinal infection is probably below the level of "travellers diarrhoea" experienced by land-based tourists to developing countries it is probably well above that of the non-travelling New Zealand and Australian population. One of the major problems facing the industry is that timelines between cruises are often very tight, allowing little time for cleaning, proper end-of-voyage medical reports, and public health interventions.
In addition, there is currently no international body which oversees healthcare or the practice of medicine on the high seas, and while some consensus-based healthcare guidelines do exist, their implementation largely rests with the particular cruise line and particular ships.
But there seems little doubt that prevention and control of gastrointestinal infections might be improved by more rigorous hygiene in food preparation, handling and storage, by passenger education about such infections and more focus on simple things like regular hand washing.
But what about the social and economic impact of cruise ships and their passengers on the places they visit? When a cruise ship arrives it sets in motion a train of economic transactions that add employment and value to the local economy.
Cruise ships certainly generate substantial revenue for ports of call through providoring, passenger spending, port taxes and other fees, with local businesses drawing heavily on the cruise ship trade.
But what social impacts might thousands of cruise passengers produce? Pack behaviour, almost as if all passengers were connected by a common behavioural umbilical cord, is the order of the day. Thousands disembark together, congregate in the terminal area, and then proceed through the city centre en masse, often producing more than a ripple of unease to run through the local population, who may well avoid the downtown area when large cruise ships are in.
But don't despair; there is some evidence of a decline in infectious disease aboard cruise ships over the last year or so. Whether this is a long-term trend remains to be seen.
In the meantime, remember that those that cruise together often get sick together, and critically, if you don't want a shipboard epidemic to sink your cruise, keep washing your hands!
Peter Curson is a professor in population and security at the University Of Sydney.