Cruise ships, with diverse populations in a confined space, are ideal for spreading infectious diseases. Photo / Getty Images

Cruise ships, with diverse populations in a confined space, are ideal for spreading infectious diseases. Photo / Getty Images

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.