The highly contagious viral bug threatening cruise holidays - and it's not COVID

You've spent months locking in excursions, flights and outfits for your dream cruise, but there is one unwanted guest that can derail even the most meticulously planned holiday in hours: norovirus.

While COVID-19 captured headlines for years, this stomach-churning gastro bug remains a constant threat at sea.

According to the Australian Centre for Disease Control, the combination of people mixing in closed spaces and longer travel times makes cruise ships a higher-risk environment for norovirus.

But while these infections can be serious - particularly for young children and those over 65 - is this something the average traveller needs to panic about? We asked the experts.

Norovirus is a virus that causes gastroenteritis, the symptoms of which include diarrhea and vomiting, explains Professor Martyn Kirk from the National Centre for Epidemiology and Population Health at the Australian National University.

He says it usually only lasts for 24-48 hours, but some people experience illness for longer.

"Norovirus is one of the most common causes of gastroenteritis in most countries around the world. The virus is spread through contaminated food or water, or from one infected person to another," Kirk tells Explore.

While people travelling on cruise ships need to be aware of the risks, they "do not need to panic", he says.

"Outbreaks of gastroenteritis due to norovirus are common on cruise ships as illness can spread quickly in closed or semi-enclosed environments ... especially where many people are sharing dining areas, bathrooms, handrails, lift buttons and other common spaces."

The main symptoms of norovirus gastroenteritis include vomiting, nausea, diarrhea, tiredness, body aches, fever and headaches, Kirk says.

The main treatment is keeping up fluids and rest.

"People can still transmit infections to other people for a few days after they have recovered," Kirk warns.

Professor Jason Mackenzie, Professor in Virology in the Department of Microbiology and Immunology at the University of Melbourne, says outbreaks are "not infrequent" on cruise ships.

And if an outbreak occurs, 20 to 30 per cent of people on board will likely contract it, he says.

"If an outbreak did occur, it would spread pretty quickly," he says.

The virus is "highly infectious" and the symptoms start to appear within about 12 hours.

"So if you contracted it from food, which is one of the normal ways of getting it, you'd be hit within that day, and it hits pretty hard and fast," Mackenzie says.

A spokesperson for Cruise Lines International Association says its member cruise lines go to "great lengths to support the health and safety of all onboard".

Crew members regularly clean and sanitise the ship's facilities, including frequent cleaning of cabins, restaurants and common areas throughout the day.

"Ships are cleaned from top to bottom using designated cleaning supplies and sanitation procedures," they say.

CLIA maintains the incidence of gastrointestinal illnesses such as norovirus is "relatively rare on cruise ships compared to other land-based settings".

On-ship protocols might include isolation on "a case-by-case" basis, if deemed necessary by a health professional.

"Isolation may involve monitoring, following up, and provision of in-service room service," they say.

CLIA recommends frequent hand washing with soap and water, especially before eating or after using the bathroom, and use of hand sanitiser.

Southern Cross Travel Insurance has identified 117 paid Australian cruise-related gastro claims between 2023 and this year so far, with the average claim approximately $1740.

"However, the cost can rise significantly when hospital care, medical transport or replacement travel is required," says Chief Customer Officer, Jess Strange.

While most gastro cases are short-lived, they can still "put a real dampener on a holiday".

"Dehydration can be a particular concern for older travellers, young children and people with underlying health conditions. In more serious cases, someone may need treatment at the ship's medical centre or, in severe cases, may need to disembark to receive treatment at a hospital," Strange says.

Travellers should ensure their travel insurance includes cruise cover, which is often an optional extra.

Depending on the cover, it may include eligible medical treatment, prescribed medication, hospital care, medical transport and necessary changes to the journey.

Travellers need to retain all medical reports, receipts and written advice for their claim.

"If they are admitted to hospital, their expenses are likely to exceed $2000, they require medical transport or they may need to change their journey, they should contact their insurer's emergency assistance team as soon as possible," Strange advises.

The Department of Agriculture, Fisheries and Forestry says if passengers are feeling unwell upon disembarking the vessel, "they should notify a biosecurity officer at the port of arrival into Australia".