The food we eat can poison us. There are over 200 known diseases that can be transmitted by food. Bacteria or viruses are the main cause of food poisoning.

Food poisoning is usually the result of poor hygiene – the people preparing the food have not washed their hands well enough or have an infection they pass on. It can also occur when the food has not been prepared properly – it is not cooked enough or not stored at the right temperature.

Some bacteria produce toxins that result in food poisoning when ingested. However, it is often the presence of particular bacteria or viruses that cause our own immune systems to produce harmful toxins. These are meant to destroy the bacteria but sometimes are harmful to us.

Food poisoning usually leads to a short acute illness (such as vomiting or diarrhoea) that resolves with appropriate medical treatment. However, in the most serious cases, food poisoning results in death.

Harmful foodborne bacteria

These are the main bacteria that give you food poisoning:

  • Campylobacter: Most strains produce a toxin that hinders the activation of the immune system, allowing the bacteria to survive in our cells for a period of time. It is the most common cause of bacterial food poisoning. In New Zealand, there are about 10,000 cases a year. It is transmitted mainly by raw chicken meat.
  • Salmonella: Toxic bacteria that cause an immune response resulting in salmonella. Symptoms include nausea, vomiting, headaches and diarrhoea. It is usually transmitted by undercooked food such as eggs and chicken and in dairy products and seafood.
  • Staphylococcus aureus: Bacteria frequently found among the normal microorganisms on skin and in nasal passages. It produces toxins in foods such as dairy products and salads.
  • Bacillus cereus: Bacteria found in starch-type food – rice, pasta or potatoes. Refrigeration slows the growth rate, but rice (and starchy foods) should not be kept any longer than 3 days. The bacteria cause mild illness with rapid onset of vomiting, with or without diarrhoea and abdominal cramping.
  • Escherichia coli: Also known as E. coli, these bacteria normally live inside your intestines. Certain types of E. coli can get from the intestines into the blood. This can happen in cows, resulting in contamination of their meat and faeces. Contaminated cow faeces (used as fertilising manure) may contaminate food (vegetables) and water. It also may be transmitted through undercooked ground beef and unpasteurised milk. It can cause kidney failure and death.
  • Clostridium botulinum: Causes botulism, which attacks the nervous system and can cause death. It can be transmitted by home-canned or badly canned goods, honey and seafood.
  • Listeria: Common in soft cheeses, pâté, precooked chicken, raw and smoked seafood and products made from unpasteurised milk. It can be life threatening for babies and the elderly.

Viruses found in food

  • Norwalk virus (norovirus) – transmitted by water, shellfish and vegetables contaminated by faeces.
  • Rotavirus – transmitted by faecal contamination of food, it is common in young children.
  • Hepatitis A – transmitted by faecal contamination of food.

Campylobacter infection reduced in New Zealand

Campylobacteriosis rates in New Zealand began to rise in the mid 1980s and peaked in 2006 with the highest rate reported internationally. This was the largest foodborne epidemic in New Zealand’s history. This epidemic was created by producing and consuming increasing amounts of contaminated chicken. Symptoms include diarrhoea, stomach cramps, tiredness, fever, nausea and vomiting. People with severe symptoms require hospital treatment and develop life-threatening complications. A small number of people die from campylobacteriosis and its complications.

Rates declined rapidly from 2007 after the New Zealand Food Safety Authority and the poultry industry introduced a range of regulations and voluntary measures aimed at reducing campylobacter on fresh chicken. The interventions included setting mandatory targets for producers to reduce campylobacter contamination of chicken meat, better hygiene practices during chicken processing and changes to the chilling processes.

Tips to avoid food poisoning

  • Wash your hands. Always wash your hands thoroughly before preparing and eating food and after using the bathroom. This helps eliminate toxin-causing bacteria and viruses.
  • Use clean surfaces and utensils. Make sure your equipment is thoroughly clean. Don’t prepare vegetables on a surface used to prepare raw meat and fish. Bacteria from the meat or fish may be transferred to the vegetables.
  • Wash fruit and vegetables.
  • Cook food properly. High temperatures may kill any toxin-producing bacteria. Cover and refrigerate food that is not going to be eaten immediately. Chilling helps to limit bacterial growth.
  • Heat leftovers well. High temperatures kill bacteria that may have started to grow.
  • Check for use-by dates. If it’s passed the expiry date, get rid of it. Toxic bacteria may be multiplying.
    Published 4 September 2012