Gastro vs food poisoning: how to tell the difference

When you are suddenly hit with nausea, vomiting, and diarrhoea, the first question is often, "Is this gastro or food poisoning?" The honest answer is that they overlap so much they are frequently impossible to tell apart from symptoms alone, and for a mild case it usually does not change what you do.

Here is the one-sentence version: gastro (gastroenteritis) is the broad term for inflammation of the stomach and intestines, most often viral and spread person to person, while food poisoning is gastroenteritis caused by contaminated food or drink; the symptoms overlap heavily and mild cases are managed the same way, with rest and fluids.

This guide explains how to tell them apart where you can, how long each lasts, how long you stay contagious, and when to see a GP.

What each term actually means

"Gastroenteritis," shortened to gastro, describes inflammation of the digestive tract that causes nausea, vomiting, diarrhoea, and cramps. Most gastro in Australia is viral, caused by viruses such as norovirus and rotavirus, and spreads from person to person or via contaminated surfaces.

Food poisoning is gastroenteritis caused specifically by eating or drinking something contaminated by bacteria (such as salmonella or campylobacter), viruses, parasites, or pre-formed toxins. So food poisoning is really a subset of gastro, defined by its source rather than by different symptoms.

How to tell them apart (and why it is hard)

There is no symptom that reliably separates the two, but a few clues can hint at the cause:

• Timing after a meal. Food poisoning sometimes begins quite suddenly, occasionally within a few hours of a suspect meal, especially toxin-related cases.
• Shared exposure. If several people who ate the same food are unwell, contaminated food is more likely.
• Spread between people. If it moves through a household, workplace, or childcare over days, a contagious virus is more likely.

For a mild illness, the distinction rarely changes management: the priority either way is rest and fluids. The cause matters more when symptoms are severe, prolonged, or there are warning signs, which is when a GP may consider testing.

How long they last and how long you are contagious

Most viral gastro settles within 1 to 3 days, though some cases last up to a week. Food poisoning also commonly resolves within a few days, depending on the cause.

For contagiousness, viral gastro can spread while you have symptoms and commonly for at least 24 to 48 hours after they stop, and longer for some viruses like norovirus. Australian public health advice is generally to stay home until at least 48 hours after vomiting and diarrhoea have stopped, which matters most if you work in food handling, healthcare, or childcare. A GP can issue a medical certificate if you need time off work or study.

When to see a GP or seek urgent care

Most cases get better on their own with rest and fluids. See a GP if you have:

• Signs of dehydration: dizziness, very dark urine, passing little urine
• Blood in your vomit or stool
• Severe or constant abdominal pain
• A high fever, or symptoms lasting more than a few days
• Higher risk: you are very young, elderly, pregnant, or have a weakened immune system

Seek urgent in-person care, or call 000, for severe dehydration, confusion, or if you cannot keep any fluids down at all. A telehealth GP can assess your symptoms, advise on rehydration and whether testing is needed, and tell you if you need to be seen in person. For ongoing symptom information, see our gastro condition guide.

Where NewDoc fits

NewDoc is a pure telehealth general practice. An Australian-trained, FRACGP-qualified GP can assess gastro and suspected food poisoning by video or phone. They can advise on rehydration and recovery, arrange a pathology referral if testing is warranted, and issue a medical certificate if you need time off, all bulk billed at $0 out of pocket for eligible Medicare cardholders. Anything that needs hands-on assessment or urgent care is flagged and redirected.

You can book a telehealth appointment if you need to be assessed.

References

• Healthdirect, Gastroenteritis (gastro)
• Healthdirect, Food poisoning
• Healthdirect, When to call an ambulance

Written by

Dr. Jason Yu FRACGP

Chief Medical Officer, NewDoc

A practising GP with over a decade of clinical experience, specialising in allergies, metabolic health, and chronic disease management.