Gastro bug or food poisoning: Cause, symptoms and prevention

Gastro outbreaks are on the rise in NSW. Dr Sam Hay explains how to decode the tummy upsets.

Dr Sam Hay

4 min read

April 27, 2023 - 6:49AM

Lifestyle

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Gastro outbreaks are on the rise in NSW.

Each year when school returns for a new term, parents see their children coming home with all sorts of illnesses. Gastro and flu are consistently high up on the list. But how can we tell if a sore tummy is food related or a virus kicking in?

So just what is the difference between food poisoning and 'gastro'?

There are many gastroenteritis infections, and many of them can originate from eating food. But classically we tend to group them into 'like' versions, and label them simple 'gastro' or 'food poisoning'.

A quick word on food poisoning: Food can lead to illness in many different ways. It can be contaminated with bacteria, viruses, parasites, or toxins. Then there's chemical contamination, allergies, or simply over-eating.

But the classic 'food poisoning' relates to toxins. Food becomes contaminated with bacteria usually from the person preparing the food. They may not have worn gloves, washed their hands, or might have used the same knives and chopping boards for meat and salads. If the food is then left out at room temperature, the bacteria bubbles away producing lots of toxins, which spread throughout the food before it is eaten.

Once ingested, this toxin can immediately trigger an effect on us poor unsuspecting patients.

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There are many gastroenteritis infections, and many of them can originate from eating food, says Dr Sam. Image: iStock

Understanding what causes gastro

Gastro

Most commonly viruses
Four predominate viruses: Rotavirus, Norovirus, Enteric Adenovirus, Astrovirus
Some bacteria, for example: Campylobacter, Salmonella, E Coli

These bugs cause illness by either producing a toxin in our bodies after they have been ingested, or they literally invade and infect the lining of the bowel.

Food Poisoning

Primarily toxin mediated
Multiple culprits including: S aureus and Bacillus cereus

How gastro is spread

Gastro

Various ways possible, the most common is the 'faecal-oral' route, from person-to-person. People just don't wash their hands after toileting. Bugs are then passed around easily.
If food is undercooked, then bugs won't be killed off.

Food Poisoning

Initial contamination of food from the person who prepared it.
As illness is from a toxin, there is very low risk of person-to-person spread.

Other common childhood illnesses parents need to know about:

All about Croup
All about Hand, Foot and Mouth
All about RSV (Respiratory Syncytial Virus)
Do kids need a COVID test every time they’re sick?

Initial contamination of food from the person who prepared it. Image: iStock

The symptoms of gastro and food poisoning

Gastro

Onset of symptoms takes a day or two to come on, and often builds up over hours.
Watery diarrhoea is the primary symptom.
Tummy cramps, nausea, and vomiting will be seen, but to varying degrees.

Food Poisoning

Onset is sudden and dramatic, usually within 1-6 hours of ingestion.
Nausea and vomiting predominate.
Tummy cramps and diarrhoea tend to only occur occasionally.

The duration of the 'bug'

Gastro

A few days. But maybe up to a whooping two weeks!

Food Poisoning

Generally comes and goes quickly over 24 hours.

Remember to keep the family hydrated when a tummy upset occurs. Image: iStock

How to diagnose gastro or food poisoning

Gastro

Doctors will take a detailed history and conduct a thorough examination.
Tests are not required for the vast majority of cases. But if symptoms persist they may ask you to send some stool samples off for testing.

Food Poisoning

Circumstances are usually classic with this one
Small clusters of people are often affected. For example, whoever ate one particular dish at the restaurant.
Tests are next to useless, so doctors rely on a good history and examination.

Complications that can arise after food poisoning or gastro

The complications are the same regardless of the cause, but are more likely in babies and pregnant women.

Dehydration is by far and away the biggest issue with any gastroenteritis illness. Vomiting and diarrhoea cause a massive loss of water from the body. Plus, nausea and vomiting just makes it damned hard to drink enough.

The more dramatic the Ds and Vs, the faster dehydration will set in, so be on the watch out for the floppy, drowsy, listless kids (plus mums and dads!).

Some infections can cause other complications through the body such as brain infection, kidney failure, or persisting lactose intolerance.

Never underestimate the importance of washing your hands. Image: iStock

How to prevent tummy upsets

Prevention is certainly the key when it comes to these illnesses.

Food needs to be prepared and stored well, never left out in the open at room temperature for any longer than a couple of hours. In fact, as Aussie temperatures soar above 32 degrees, an hour is regarded as maximum – so be careful of those long grazing summer lunches.

Avoid cross-contamination by washing knives and chopping boards regularly, and keeping raw meats and other foods well separated.

Wash hands, wash hands, wash hands!

If the food looks dodgy – don't eat it! Poorly maintained foods in bain marie's are perfect brewing pots for bugs and their toxins. If food looks old or poorly looked after, then it's best to give it a miss.

Quarantine the sick ones.

Gastro spreads so well from dirty mucky hands covered in bug-laden vomit or poo. Some bugs can even be spread through tiny droplets from coughs, sneezes or wayward vomit sprays (yuck!!!). So often the best strategy is to separate the sick ones from the rest of the family. And this includes making sure no one shares plates, cups, and drink bottles.

Remember, if you're concerned about anything presenting in your home - tummy bug or otherwise - speak to your local GP or healthcare professional.

This article was first published in October 2017 and updated in January 2023.