When does food poisoning start

On this page

• What is food poisoning?
• What are the symptoms and causes of food poisoning?
• What are the high-risk groups for food poisoning?
• How is food poisoning treated?
• Related information on Australian websites

What is food poisoning?

Food poisoning is caused by bacteria, viruses or toxins in the food we eat. Some of these toxins are found naturally in foods, while some have accumulated in the environment.

If you have food poisoning you’ll probably have gastroenteritis symptoms such as abdominal cramps, diarrhoea or vomiting, or flu-like symptoms. Food poisoning can also cause serious long-term problems like kidney failure. Occasionally people die from food poisoning.

Some wild mushrooms, including the death cap, are extremely poisonous. You should not eat wild-harvested mushrooms unless they have been definitely identified as safe. Seek immediate medical treatment If you think you may have eaten poisonous mushrooms.

Large fish, such as shark, swordfish and marlin, may accumulate relatively high levels of mercury. You should limit your consumption of these fish, especially if you are a child, are pregnant or planning pregnancy.

What are the symptoms and causes of food poisoning?

You may be sick with food poisoning but not know what food caused it or even that you have it. Different bacteria and viruses can have different effects:

• Salmonella: gastro and flu-like symptoms can appear between 8 and 72 hours (usually 12 to 36 hours) after eating the infected food and last for 2 to 5 days.
• Campylobacter: gastro symptoms appear in 2 to 5 days, and last for 2 to 10 days.
• Listeria: gastro or flu-like symptoms usually appear within 3 weeks, but can take up to 70 days.
• Norovirus or rotavirus: severe gastro or flu-like symptoms usually begin 24 to 48 hours after exposure and last 1 or 2 days (norovirus) or up to 6 days (rotavirus).
• E. coli: gastro symptoms usually appear in 3 to 4 days and last about 1 week.

Food needs to be stored, handled and cooked carefully and at temperatures that avoid the spread and growth of bacteria that can make you sick. Read about preparing food safely.

What are the high-risk groups for food poisoning?

If you’re pregnant, elderly or very young, or your immune system is weak through illness or drugs, you’re at greater risk of food poisoning and possibly serious complications.

If you’re pregnant, listeria can cause you to miscarry, even if you don’t know you’ve been infected. If you notice symptoms — usually like a mild flu but also diarrhoea, vomiting and nausea — contact your doctor immediately.

Read more about how to avoid listeria on the Pregnancy, Birth and Baby website.

How is food poisoning treated?

Most people don’t need medical help for food poisoning, as their symptoms are not severe and don’t last long. However, people in high-risk groups (such as babies and elderly people) should see a doctor early on, to make sure they don’t get dehydrated.

For children, see your GP or call healthdirect on 1800 022 222 (known as NURSE-ON-CALL in Victoria) if your child has diarrhoea that lasts for more than a few days or has bloody diarrhoea.

Take your child to the emergency department immediately if:

• your child has symptoms of food poisoning and is less than 1 year old
• your child has severe stomach pain and vomiting and can’t keep fluid down
• your child isn’t drinking and has signs of dehydration, including little or no wee, weight loss, tiredness and extreme thirst
• you’re worried about your child being extremely unwell

For adults, seek medical advice if:

• you still have symptoms after 3 days, or your symptoms are very severe
• you still can’t keep any fluids down, more than 24 hours after getting sick
• there is blood or mucus in your vomit or diarrhoea

For a mild case of food poisoning, you may try sucking ice chips, replacing lost fluids and electrolytes (you can buy an oral rehydration solution from your pharmacy) and easing back into your normal diet and routine when you feel ready. Antibiotics may help with some bacterial types of food poisoning, but are usually not needed.

Food can become contaminated at any stage during its production, processing or cooking.

For example, it can become contaminated by:

• not cooking food thoroughly (particularly meat)
• not correctly storing food that needs to be chilled at below 5C
• keeping cooked food unrefrigerated for a long period
• eating food that has been touched by someone who is ill or has been in contact with someone with diarrhoea and vomiting
• cross-contamination (where harmful bacteria are spread between food, surfaces and equipment)

Cross-contamination can occur, for example, if you prepare raw chicken on a chopping board and don't wash the board before preparing food that won't be cooked (such as salad), as the harmful bacteria can be spread from the chopping board to the salad.

It can also occur if raw meat is stored above ready-to-eat meals and juices from the meat drip on to the food below.

See preventing food poisoning for information about reducing these risks

Types of infection

Food contamination is usually caused by bacteria, but it can also sometimes be caused by viruses or parasites. Some of the main sources of contamination are described below.

Campylobacter

In the UK, campylobacter bacteria are the most common cause of food poisoning. The bacteria are usually found on raw or undercooked meat (particularly poultry), unpasteurised milk and untreated water.

The incubation period (the time between eating contaminated food and the start of symptoms) for food poisoning caused by campylobacter is usually between two and five days. The symptoms usually last less than a week.

Salmonella

Salmonella bacteria are often found in raw or undercooked meat, raw eggs, milk, and other dairy products.

The incubation period is usually between 12 and 72 hours. The symptoms usually last around four to seven days.

Listeria

Listeria bacteria may be found in a range of chilled, "ready-to-eat" foods, including pre-packed sandwiches, cooked sliced meats and pâté, and soft cheeses (such as Brie or Camembert).

All of these foods should be eaten by their "use-by" dates. This is particularly important for pregnant women, because a listeria infection (known as listeriosis) in pregnancy can cause pregnancy and birth complications, and can result in miscarriage.

The incubation period can vary considerably, from a few days to several weeks. The symptoms will usually pass within three days.

Escherichia coli (E. coli)

Escherichia coli, often known as E. coli, are bacteria found in the digestive systems of many animals, including humans. Most strains are harmless but some can cause serious illness.

Most cases of E. coli food poisoning occur after eating undercooked beef (particularly mince, burgers and meatballs) or drinking unpasteurised milk.

The incubation period for food poisoning caused by E. coli is typically one to eight days. The symptoms usually last for a few days or weeks.

Shigella

Shigella bacteria can contaminate any food that has been washed in contaminated water.

Symptoms typically develop within seven days of eating contaminated food and last for up to a week.

An infection caused by Shigella bacteria is known as bacillary dysentery or shigellosis. See the topic on dysentery for more information about it.

Viruses

The virus that most commonly causes diarrhoea and vomiting is the norovirus. It's easily spread from person to person, through contaminated food or water. Raw shellfish, particularly oysters, can also be a source of infection.

The incubation period typically lasts 24-48 hours and the symptoms usually pass in a couple of days.

In young children, the rotavirus is a common cause of infection from contaminated food. The symptoms usually develop within a week and pass in around five to seven days.

Parasites

In the UK, food poisoning caused by parasites is rare. It's much more common in the developing world.

Parasitic infections that can be spread in contaminated food include:

• giardiasis – an infection caused by a parasite called Giardia intestinalis
• cryptosporidiosis – an infection caused by a parasite called Cryptosporidium
• ameobiasis – a type of dysentery caused by a single-cell parasite (ameoba) called Entamoeba histolytica (this is very rare in the UK)

The symptoms of food poisoning caused by a parasite usually develop within 10 days of eating contaminated food, although sometimes it may be weeks before you feel unwell.

If left untreated, the symptoms can last a long time – sometimes several weeks or even a few months.