Understanding the concept of food poisoning

By Anna Mhalu, Quality Assurance Officer

Food poisoning is an illness caused by eating foods or drinking water that has harmful bacteria, bacterial toxins, parasites or viruses. These harmful germs are mostly found in raw meat, chicken, fish, and eggs, but they can spread to any type of food. They can also grow on food that is left out on counters or outdoors or is stored too long before you eat it. Sometimes food poisoning happens when people do not wash their hands before they touch food. Food poisoning can also occur when non-infectious poisons (such as poisonous mushrooms), pesticides or heavy metals (such as lead or mercury) find their way into people's stomachs.

Most of the time, food poisoning is mild and goes away after a few days. All you can do is wait for your body to get rid of the germ that is causing the illness. But some types of food poisoning may be more serious, and you may need to see a doctor. People at greatest risk for food poisoning are seniors, pregnant women, young children and babies, and people with chronic medical conditions (e.g., diabetes, AIDS, liver disease).

Food poisoning caused by pathogenic bacteria still occurs at unacceptably high frequencies in industrialized nations and developing countries. The year 2008 recorded an unprecedented incidence of foodborne diseases in the African Region including; anthrax in Zimbabwe; typhoid fever in Uganda and chemical poisoning due to consumption of seed beans and maize in Nigeria and Kenya. Also, cholera was reported in several countries including Mozambique, Nigeria, Congo, Zambia, DRC, Kenya, Tanzania, South Africa and Zimbabwe; while pesticide poisoning from cabbage and other vegetables was reported in in Senegal. Fish mouse was reported in Mauritius; mushroom poisoning in Algeria; Botulism and Hepatitis A in Uganda and Gala Night Dinner Meal in Nigeria (WHO).

Food poisoning occurs when contaminated food or water is ingested. Contamination can occur anywhere along the process of obtaining and eating food – it can occur during growing, harvesting, processing, storing, or preparation stages. In most cases, bacteria, viruses, or parasites are transferred to food from other sources, making these organisms the most common causes of food poisoning. However, in some less common types of food poisoning, the poison or toxin is naturally part of the food (e.g., poisonous mushrooms or fish). Other less common causes include shellfish and insecticides.

Bacteria and bacterial toxins

Many bacteria can cause food poisoning, either directly or by the toxins they produce. Some of the most common include Salmonella, E. coli, Vibrio cholera, Shigella, Staphylococcus, and Clostridium perfringens. Many bacterial causes of food poisoning can be found in undercooked meats, poultry, eggs, dairy, processed meats, fish, custards, cream pies, and contaminated water.


Norovirus and other viruses can cause food poisoning, most commonly through contaminated raw or uncooked produce and shellfish from contaminated water.


Parasites such a giardia lamblia can also cause food poisoning through contaminated produce and water.


Dozens of species can cause muscarine poisoning. These poisons attack the central nervous system, causing partial or complete paralysis in severe cases.

Chemical contaminants

Contamination of foods may occur through environmental pollution of the air, water and soil, such as the case with toxic metals, polychlorinated biphenyls (PCBs) and dioxins. Other chemical hazards, such as naturally occurring toxicants, may arise at various points during food production, harvest, processing and preparation. The improper use of various chemicals such as food additives, pesticides (i.e. organophosphates), veterinary drugs and other agro-chemicals may contribute to food poisoning.

The common symptom of food poisoning is usually diarrhea. You may also feel sick to your stomach, vomit, or have stomach cramps. Some food poisoning can cause a high fever and blood in your stool. How you feel when you have food poisoning mostly depends on how healthy you are and what germ is making you sick.

If you vomit or have diarrhea a lot, you can get dehydrated. Dehydration means that your body has lost too much fluid. Watch for signs of dehydration, which include having a dry mouth, feeling lightheaded, and passing only a little dark urine. Children and the elderly can get dehydrated very quickly and should be watched closely. Pregnant women should always call a doctor if they think they may have food poisoning.

Increased public awareness of the health-related and economic impact of food-borne contamination and illness has resulted in greater efforts to develop more sensitive methods of pathogen detection and identification and detection of chemical contaminants (i.e. PCR and chromatographic techniques). The maximum acceptable levels of these contaminants are specified in national standards (i.e. Tanzania standards) and other international standards/regulations such as Codex Alimentarius and ISO standards. These standards and regulations are enforced and monitored by national regulatory bodies including TBS through food inspection, testing and promotion of public awareness on public health issues.

Role of food handlers and consumers in prevention of food poisoning

Wash hands thoroughly with soap and hot water and dry them before handling food, after handling raw foods including meat, fish, eggs, fruits and vegetables, as well as after touching the bin, going to the toilet, blowing nose, or touching animals, including pets.

If you are ill with diarrhea or vomiting, do not prepare food for others, especially infants, the elderly, and those with weakened immune systems since they are more vulnerable to infection. In addition, do the following:

• Wash worktops before and after preparing food, particularly after they have been touched by raw meat, including poultry, raw eggs, fish and vegetables with hot soapy water.

• Wash dishcloths and towels regularly and let them dry before you use them again. Dirty, damp cloths are the perfect place for bacteria to breed.

• Wash raw vegetables and fruits thoroughly before eating, especially those that will not be cooked.

• Always cover raw meat and store it on the separate shelf of the fridge, where it can’t touch other foods or drip onto them.

• Make sure that food from animal sources (meat, dairy, eggs) is cooked thoroughly or pasteurized.

• Keep your fridge temperature below 5°C. By keeping food cold, you stop food poisoning bugs growing

• Cook foods until they are steaming hot, especially leftover foods or ready-to-eat foods.

• Use safe water and raw material.

• Don’t eat food that’s past its “use-by” date label. These are based on scientific tests that show how quickly harmful bugs can develop in the packaged food.

• Eat food from reliable source and which is approved by the regulatory authorities.

Food handlers can also ensure food safety by implementing systems which will ensure safety monitoring in all production/processing chain (i.e. HACCP and ISO 22000).