What Is Food Poisoning?

  • Suruthy Mary JosephBachelor in Biomedical Science (IBMS)- BSc in University of Portsmouth
  • Richa Lal             MBBS, PG Anaesthesia (University of Mumbai)


Food is a basic need for every living species to sustain life. Food can undergo contamination by various factors making it unsafe to consume and developing a foodborne illness. Contamination can occur when packaging, processing, distributing or storing the food products. Food safety and nutrition work best together.

Unhealthy food increases the chances of promoting and creating a vicious cycle of infectious disease, undernutrition and deficiencies. According to Public Health England, 17 million cases of intestinal infectious disease are reported annually in the UK. Consumption of food contaminated with foodborne pathogens (bacteria, virus, parasites, fungi and their toxins and chemicals) can be from livestock, poultry, or plant sources and this can lead to food poisoning / foodborne illness.1 Food poisoning cases may also occur due to food handlers not maintaining the etiquette of food safety. 2

The faecal-oral route is the primary transmission mode of foodborne pathogens. Some examples are the non-typhoidal Salmonella and Campylobacter causing food poisoning symptoms. Both bacteria reside in animals and the transmission of diseases from animals to humans is called zoonotic transmission of disease. 

Common types of food poisoning

Bacterial food poisoning

Bacteria like Salmonella, Clostridium, Staphylococcus, Campylobacter, Vibrio, Listeria, and E. coli can lead to symptoms from simple gastroenteritis to severe systemic involvement of other organs such as the liver, kidney and neurologic manifestations due to bacterial toxins activity. 

Food poisoning bacteria causes foodborne illness via these three mechanisms:

  • Ingestion of pre-existing toxins formed in the food causes intoxication e.g.in case of  Staphylococcus aureus 
  • Ingestion of bacterium and production of its toxins within the gut e.g. in the case of Clostridium perfringens
  • Infection of the gut lining cell or epithelial cells is seen in Salmonella infections 

Let’s discuss the common food-poisoning bacteria:

About a million people are afflicted by these common pathogens yearly. The symptoms include headache, fever, nausea, vomiting, stomach pain and diarrhoea. The main source of Salmonella infection (Salmonellosis) is from animal products such as poultry, eggs, and others. 

The source of Campylobacter is improper food handling and consumption of raw milk, undercooked poultry, other meat items. and contaminated water.

Enterohemorrhagic (E.coli) enters the body by ingesting contaminated fresh fruits and vegetables, animal products, raw meat and unpasteurised milk

  • Listeria

Listeria infection (Listeriosis) is associated with the risk of spontaneous abortions and stillbirths. The source of it includes unpasteurised dairy products and other ready-to-eat foods. Listeria bacterium can even grow at low temperatures of refrigeration

They exist in contaminated water and food. The reported food poisoning of cholera is from seafood varieties, rice, vegetables, and millet gruel. The symptoms include vomiting, abdominal pain, and profuse watery diarrhoea.3 Thus, it results in the loss of ample amounts of water and electrolytes from the body leading to severe dehydration and even death in some cases

Viral food poisoning

Viruses are a typical source causing gastrointestinal disease. Norovirus is a common virus causing foodborne illnesses. Sources include contaminated raw food and fish consumption.

Parasitic food poisoning

Parasites are present in the water and soil. Food consumed without proper washing or cooking is a good source of such infections. The parasite enters the food cycle affecting humans with foodborne illness. Some examples include tapeworms such as Echinococcus, Taenia, and others like Ascaris, Cryptosporidium, Entamoeba histolytica or Giardia.


The symptoms can range from mild gastroenteritis to severe paralysis. All patients inflicted by foodborne illness of various causes initially demonstrate similar symptoms such as:

  • Fever
  • Nausea
  • Vomiting 
  • Stomach cramps
  • Diarrhoea

Normally, the food-borne illness subsides within a week. The patients recover without any extensive treatments. Severe cases of food poisoning show these symptoms:

  • Bloody diarrhoea
  • High-grade fever
  • Vomiting
  • Severe dehydration symptoms


The causes of foodborne poisoning can arise from anywhere and from different sources.7

  • Due to urbanisation and busy life, people prefer to eat outside in restaurants, cafeterias, bakeries and streets where food safety, hygiene and handling become questionable
  • Unorganised waste disposal and inadequate recycling of spoiled food leads to piling up of day-to-day food waste and can cause increased pests and insects breeding around the food. This creates a vehicle for foodborne illnesses
  • Poor infrastructure–Lack of inspection, inadequate storage or thawing of food before preparation for too long, and reheating cooked food but not reaching the appropriate temperature and time can lead to the growth of pathogens.4 Mixing infected food through utensils and equipment while cooking can result in cross-contamination


  • Parasites are detected using microscopical observation of faecal samples
  • E.coli, Salmonella and Campylobacter are identified by microbial culturing and isolating the organism by biochemical identification. Serotyping identifies different species. ELISA (enzyme-linked immunosorbent assay) and other assays are used to verify toxins
  • Viruses are difficult to culture. Different molecular techniques like PCR (polymerase chain reaction) are used to detect the genes in viruses.5 Newer innovative methods like molecular and biosensor techniques are rapid, simple, sensitive and specific towards different species


  • The treatment is about the replacement of lost fluids and electrolytes. Oral rehydration  solutions are also a replacement prescription to prevent dehydration
  • Antidiarrheal medication can relieve diarrhoea and stomach cramps
  • Antibiotics treat foodborne illnesses caused by bacteria. Meanwhile, the excess usage of antibiotics can result in drug resistance to pathogens. Therefore, the action of antibiotics becomes unsuccessful against certain infectious diseases


Food Standards agencies must inform any food related incidents to environmental health officers or Public health departments.6 Food standards agencies have taken responsibility by maintaining food safety and prioritising public health. 

They include:

  • To provide details of composition and nutrition supplied in the food products
  • Enforcing some necessary laws and regulations to ensure that the food supplies from various industries are safe to consume
  • To eliminate any toxins or food alteration (adulterants) within the food, institute legal proceedings against economic fraud through continuously monitoring and supervising the food supply chain

World Health Organization (WHO) has implemented five key steps for safer food.

  • Keep clean from preparation to delivery of food.
  • Make use of different platforms for preparing raw food and cooked food.
  • Maintaining safe temperature.
  • Cooking carefully with attention.
  • Usage of clean water.

Microbiological hazards are preventable by maintaining the cold chains in the industry. The retail shops stop cross-contamination by implementing safe food manufacturing practices, food safety training and education practices for food handlers. 

Some traditional preventive methods employed to prevent bacteria growth and food decay are mentioned below.

  • Chilling
  • Freezing
  • Nutrient restriction
  • Reduction of water activity
  • Acidification
  • Pasteurisation
  • Sterilisation
  • Fermentation 
  • Chemical/biological antimicrobials
  • Microbial irradiation can reduce food poisoning bacteria
  • Ozone treatment

Complications and risks of food poisoning

The long-term effects of bacterial infectious disease can lead to post-infection sequelae and even death without proper management. 

The high-risk group includes immunocompromised patients, children and older age groups. Nevertheless, the individuals out of the risk group may also be affected. 

Some of the complications witnessed are:


Food is a basic necessity for humans but sometimes it can get contaminated with micro-organisms like bacteria, viruses, toxins and chemicals and become unsafe to consume. The common symptoms include nausea, vomiting, diarrhoea, fever and stomach pain. 

Most of the time food poisoning can subside within a week without extensive treatment. 

However, it can lead to complications like dehydration and even death. Therefore, managing and preventing foodborne illness is extremely important and the main preventive measure is practising hygiene.


  1. Bintsis T. Foodborne pathogens. AIMS Microbiol [Internet]. 2017 Jun 29 [cited 2023 Dec 14];3(3):529–63. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6604998/
  2. Antunes P, Novais C, Peixe L. Food-to-humans bacterial transmission. Baquero F, Bouza E, Gutiérrez-Fuentes JA, Coque TM, editors. Microbiol Spectr [Internet]. 2020 Jan 16 [cited 2023 Mar 11];8(1):8.1.1. Available from: https://journals.asm.org/doi/10.1128/microbiolspec.MTBP-0019-2016
  3. Fung F, Wang HS, Menon S. Food safety in the 21st century. Biomed J [Internet]. 2018 Apr [cited 2023 Mar 11];41(2):88–95. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6138766/
  4. Gargiulo AH, Duarte SG, Campos GZ, Landgraf M, Franco BDGM, Pinto UM. Food safety issues related to eating in and eating out. Microorganisms [Internet]. 2022 Oct 26 [cited 2023 Mar 11];10(11):2118. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9695559/
  5. Zhang M, Wu J, Shi Z, Cao A, Fang W, Yan D, et al. Molecular methods for identification and quantification of foodborne pathogens. Molecules [Internet]. 2022 Nov 26 [cited 2023 Mar 11];27(23):8262. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9737419/
  6. Gizaw Z. Public health risks related to food safety issues in the food market: a systematic literature review. Environmental Health and Preventive Medicine [Internet]. 2019 Nov 30 [cited 2023 Dec 14];24(1):68. Available from: https://doi.org/10.1186/s12199-019-0825-5
  7. Tropea A. Microbial contamination and public health: an overview. Int J Environ Res Public Health [Internet]. 2022 Jun 17 [cited 2023 Mar 11];19(12):7441. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9224327/
  8. Tam K, Torres VJ. Staphylococcus aureus secreted toxins & extracellular enzymes. Microbiol Spectr [Internet]. 2019 Mar [cited 2023 Dec 15];7(2):10.1128/microbiolspec.GPP3-0039–2018. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6422052/
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Asra Runissa

Master of Science - MS, medical biochemistry Kasturba Medical College, Mangalore

I am Asrarunissa from India. I hold a bachelor's degree in Biomedical science from Nitte university and M.Sc. in Medical Biochemistry from Manipal university. I was been working as a biochemistry lecturer for Physiotherapy students. I love to build my knowledge and also impart it to those who require it, which is what exactly I m doing right now being a medical writer at Klarity. Dedicating ample amount of time, to researching and developing an article that ultimately benefits society at large.

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