Is Bali belly contagious? What spreads, and for how long

Why the answer is it depends

Bali belly is a nickname covering a whole family of infections, and they behave very differently. Some spread person to person readily. Some barely do at all and need the contaminated food or water to make the trip themselves.

Viruses are the contagious end. Norovirus and rotavirus move between people with very little help. Bacteria such as Salmonella, Campylobacter and E. coli mostly arrive via food and water, though poor hand hygiene will carry them from one person to the next. Parasites like Giardia spread through faeces reaching a mouth, which happens more easily than anyone likes to think about.

Since you will almost never know which one you have, and a stool test takes days you do not have on holiday, the sensible move is to assume the worst case and behave accordingly for a couple of days.

Norovirus, the one that takes out a whole villa

If four people go down within about 48 hours of each other, norovirus is the usual explanation. healthdirect does not hedge about it.

It is highly contagious. This means it spreads easily from person to person.

It spreads through contact with an infected person's faeces and through contaminated airborne droplets, which is the part people miss: vomiting puts virus into the air of a small bathroom, and the next person in does not need to touch anything to be exposed.

Symptoms typically start within 1 to 2 days of exposure and resolve within 1 to 3 days. And the single most useful sentence in this entire article, because it contradicts what every traveller instinctively reaches for:

Alcohol-based hand sanitisers do not kill norovirus, so use soap and water.

The bottle of hand gel in your day pack is not useless, it is just not the right tool here. Soap and running water, for twenty seconds, is.

How long is someone contagious?

Longer than they feel unwell, which is the trap. People go back to the pool bar the moment they feel human again and restart the chain.

The Australian public health rule for gastroenteritis is clear and it is the number to use:

Children and adults should not return to school or work until 48 hours after the last episode of diarrhoea and or vomiting.

For norovirus specifically, healthdirect advises avoiding preparing food for others for at least 2 days after symptoms stop, and healthcare workers are told to stay away for 48 to 72 hours. For giardiasis the exclusion is shorter, until there has been no diarrhoea for at least 24 hours.

On a holiday nobody is going to sit out 48 hours of Bali in a room, and pretending otherwise is useless advice. The workable version: the unwell person does not handle anyone else's food, drinks or ice for two days after they stop, and everyone washes their hands properly. That gets you most of the benefit without writing off half the trip.

The rules that actually work in a shared villa

• Soap and water, not gel. Twenty seconds, before anyone eats or handles food, and after every bathroom trip.
• One bathroom for the unwell person if the villa has more than one. If it does not, they flush with the lid down and wipe the taps and handle afterwards.
• Nobody sick touches shared food. No serving, no scooping ice, no passing around the fruit plate, no sharing a water bottle.
• Own towel, own bottle, own glass. Label them if you have to. This is where it usually goes wrong.
• Wash the sheets and towels hot if someone has vomited, and wash your hands after handling them.
• Tell the villa staff. They would much rather know and clean properly than find out later, and they deal with this constantly.

None of this is Bali specific. It is the same advice healthdirect gives for gastro in an Australian household, which is the point: this is an ordinary infection in an unfamiliar place.

Or did you all just eat the same thing?

Worth considering before anyone is blamed. If your group ate together and people start going down within a similar window, a shared source is at least as likely as person to person spread. Different people have different incubation periods and different amounts of the same bug, so identical exposure can look like a chain of infection.

You will probably never know. The Better Health Channel notes that a cause is never identified in roughly a fifth to half of all cases of traveller's diarrhoea, and holiday cases are almost never investigated at all because everyone is better before the result would come back.

It does not change what you do. Fluids, hygiene, and a doctor if the red flags on the main Bali belly page show up.

With kids, and who to worry about

Children are the most efficient spreaders in any household and the most vulnerable to dehydration, which is an unhappy combination. Nappies, hands and mouths do most of the work, and a toddler cannot be reasoned with about hand washing.

The thresholds are lower for them. healthdirect is explicit that anti-diarrhoeal medicines should not be used to treat diarrhoea in children, so rehydration is the whole plan, and a doctor sooner rather than later. The advice for travelling with children generally is on Bali with kids, including the water rules for bottles and formula.

The same caution applies to older travellers, anyone pregnant, and anyone managing a medical condition or taking medication that affects the gut. In those cases the wait-and-see window is much shorter and a clinic visit is a reasonable first move rather than a last one.