Topic 2 Most common foodborne pathogens

Foodborne outbreaks may be caused by several agents, typically detected in the people affected, in the implicated food vehicle, or in the food chain. Causative agents include bacteria and their toxins, viruses, parasites, fungi, and other agents.

Most foodborne outbreaks are caused by bacteria such as Campylobacter, Salmonella, Yersinia, Shigatoxin-producing Escherichia coli, or Listeria monocytogenes.

Foodborne illnesses and outbreaks may also result from consumption of food contaminated with toxins released by bacteria such as Bacillus cereus, Clostridium botulinum, Clostridium perfringens, Staphylococcus aureus in certain types of food, in specific conditions.

Norovirus is the most frequently detected agent in outbreaks caused by viruses. Other viruses such as hepatitis A and other uncommon viruses are less frequently reported but nevertheless have the potential to cause extensive outbreaks in the community, depending on the type of food and the mechanisms leading to food contamination (e.g. frozen products).

Parasites contributing to the overall burden of foodborne diseases in Europe include all the protozoan and helminth parasites transmitted to humans through food, such as Trichinella, Toxoplasma, Cryptosporidium and Giardia (EFSA, 2021).

Salmonella is commonly found in the intestines of healthy birds and mammals (European Food Safety Authority, n.d.). Risk of infection in humans is associated with the consumption of contaminated food, mainly poultry (e.g. chicken, turkey), eggs, meat (e.g. beef, pork), fruits and vegetables contaminated by manure, and even processed foods, such as nut butters (Centers for Disease Control and Prevention, 2022).

The consumption of food contaminated with Salmonella leads to a disease called salmonellosis. The most usual symptoms include acute fever, abdominal pain, diarrhoea, nausea and sometimes vomiting (World Health Organisation, 2018). The onset of salmonellosis symptoms occurs 6 – 72 hours (usually 12 – 36 hours) after the consumption of contaminated food, but the symptoms are relatively mild (World Health Organisation, 2018). Most people recover within 4 to 7 days without antibiotic treatment (Centers for Disease Control and Prevention, 2022).

The most important measure of salmonellosis prevention is the thorough cooking of meat, poultry and egg products (Minnesota Dept. of Health, n.d.). Raw or undercooked eggs should be avoided, while pasteurized eggs should be used in foods that do not require cooking, such as hollandaise sauce, salad dressing, uncooked pies, or homemade ice cream (Minnesota Dept. of Health, n.d.). Salmonella is killed in temperatures higher than 73°C (Science of cooking, n.d.).

Campylobacter is 1 of 4 key global causes of diarrhoeal diseases. It is considered to be the most common bacterial cause of human gastroenteritis in the world. Campylobacter infections are generally mild, but can be fatal among very young children, elderly, and immunosuppressed individuals. Campylobacter species can be killed by heat after thorough cooking. To prevent Campylobacter infections, make sure to follow basic food hygiene practices when preparing food (World Health Organization, 2020).

The onset of disease symptoms usually occurs 2 to 5 days after infection with the bacteria, but can range from 1 to 10 days. The most common clinical symptoms of Campylobacter infections include diarrhoea (frequently bloody), abdominal pain, fever, headache, nausea, and/or vomiting. The symptoms typically last 3 to 6 days (World Health Organization, 2020).

There are a number of strategies that can be used to prevent disease from Campylobacter. Prevention is based on control measures at all stages of the food chain, from agricultural production on a farm, to processing, manufacturing and preparation of foods both commercially and domestically. Good hygienic slaughtering practices reduce the contamination of carcasses by faeces, but will not guarantee the absence of Campylobacter from meat and meat products.  Bactericidal treatment, such as heating (for example, cooking or pasteurization) or irradiation, is the only effective method of eliminating Campylobacter from contaminated foods (World Health Organization, 2020).

Escherichia coli (E. coli) is a bacterium that is commonly found in the lower intestine of humans. Most E.coli strains are harmless, but some can cause serious food poisoning (World Health Organization, 2018).

Shiga toxin-producing E. coli (STEC) is a bacterium that can cause severe foodborne disease. Primary sources of STEC outbreaks are raw or undercooked ground meat products, raw milk, and faecal contamination of vegetables (World Health Organization, 2018).

In most cases, the illness is self-limiting, but it may lead to a life-threatening disease including haemolytic uraemic syndrome (HUS), especially in young children and the elderly (World Health Organization, 2018).

STEC is heat-sensitive. When preparing food, a food handler must be sure to follow basic food hygiene practices such as “cook thoroughly” (World Health Organization, 2018).

Symptoms of the infection by STEC include abdominal cramps and diarrhoea that may in some cases progress to bloody diarrhoea (haemorrhagic colitis). Fever and vomiting may also occur. The incubation period can range from 3 to 8 days. The prevention of infection requires control measures at all stages of the food chain, from agricultural production on the farm to processing, manufacturing and preparation of foods in both commercial establishments and household kitchens.

Clostridium botulinum is a bacterium that produces dangerous toxins under low-oxygen conditions. Botulinum toxins are one of the most lethal substances known. They block nerve functions and can lead to respiratory and muscular paralysis. Foodborne botulism, caused by consumption of improperly processed food, is a rare but potentially fatal disease if not diagnosed rapidly and treated with antitoxin. Canned, preserved or fermented foodstuffs are a common source of foodborne botulism and their preparation requires extra caution (World Health Organisation, 2018).

Early symptoms include marked fatigue, weakness and vertigo, usually followed by blurred vision, dry mouth and difficulty in swallowing and speaking. Vomiting, diarrhoea, constipation and abdominal swelling may also occur (World Health Organisation, 2018).

Prevention of foodborne botulism is based on good practice in food preparation particularly during heating/sterilization and hygiene. Foodborne botulism may be prevented by the inactivation of the bacterium and its spores in heat-sterilized  canned products or by inhibiting bacterial growth and toxin production in other products. The vegetative forms of bacteria can be destroyed by boiling but the spores can remain viable after boiling even for several hours. However, the spores can be killed by very high temperature treatments such as commercial canning (World Health Organisation, 2018).

Staphylococcus aureus is commonly found on the skin, throats and nostrils of healthy people and animals. Therefore, it usually doesn’t cause illness unless it is transmitted to food products where it can multiply and produce harmful toxins. Staphylococcal symptoms include nausea, stomach cramps, vomiting or diarrhoea. Staphylococcal bacteria can be destroyed by cooking but their toxins are heat resistant and cannot be destroyed (Gordon, 2019).

The bacteria can be found in unpasteurized dairy products and salty foods such as ham and other sliced meats. Foods that are made or come in contact with hands and require no additional cooking are at highest risk, including: salads, such as ham, egg, tuna, chicken, potato and macaroni, bakery products, such as cream-filled pastries, cream pies and chocolate éclairs, sandwiches (Gordon, 2019).

Foods must be kept out of the temperature danger zone and kitchen areas must be kept clean. Hands should be washed with soap and water, while food handlers should not prepare or serve food if they have a nose or eye infection or wounds or skin infections on their hands or wrists (Gordon, 2019).

Foodborne listeriosis is one of the most serious and severe foodborne diseases. It is caused by the bacteria Listeria monocytogenes (World Health Organisation, 2018).

Unlike many other common foodborne diseases causing bacteria, L. monocytogenes can survive and multiply at low temperatures usually found in refrigerators. Eating contaminated food with high numbers of L. monocytogenes is the main route of infection (World Health Organisation, 2018).

In past outbreaks, foods involved included ready-to-eat meat products, such as frankfurters, meat spread (paté), smoked salmon and fermented raw meat sausages, as well as dairy products (including soft cheeses, unpasteurized milk and ice cream) and prepared salads (including coleslaw and bean sprouts) as well as fresh vegetables and fruits (World Health Organisation, 2018).

In general, guidance on the prevention of listeriosis is similar to guidance used to help prevent other foodborne illnesses. It is important to respect the shelf-life and storage temperature written on labels of ready-to-eat foods to ensure that bacteria potentially present in these foods does not multiply to dangerously high numbers. Cooking before eating is another very effective way to kill the bacteria (World Health Organisation, 2018).

Norovirus is the cause of significant burden of foodborne illness globally as well as in the European region. Norovirus is highly contagious and often cause outbreaks (World Health Organisation, 2015).

Norovirus infection typically causes acute gastroenteritis with the most common symptoms being nausea, vomiting, diarrhoea and stomach pain. Symptoms usually develop 12 to 48 hours after infection. The disease normally lasts between 1 and 3 days (World Health Organisation, 2015).

Virus is transmitted through the faecal-oral route, and one gets infected by consumption of contaminated food or water, by contact with an infected person, or by touching contaminated surfaces. Many different kinds of foods have been implicated in norovirus illness, including bivalve shellfish such as oysters and mussels, raw fruits and vegetables, and prepared foods. Fruits and vegetables can also be contaminated with foodborne viruses through faecal contaminated water used for irrigation, including reuse of wastewater, or washing (World Health Organisation, 2015).

The prevention of norovirus can be succeeded by good hygiene, in particular hand-hygiene, is essential – for food producers, food handlers as well as the consumers themselves. Pork products should be properly heat treated before consumption. It is recommended to avoid preparing food for others when having gastrointestinal symptoms and for at least 48 hours after symptoms stop (World Health Organisation, 2015).

Hepatitis A is an inflammation of the liver caused by the hepatitis A virus (HAV). The virus is primarily spread when an uninfected (and unvaccinated) person ingests food or water that is contaminated with the faeces of an infected person (World Health Organisation, 2022).

Unlike hepatitis B and C, hepatitis A does not cause chronic liver disease but it can cause debilitating symptoms and rarely fulminant hepatitis (acute liver failure), which is often fatal (World Health Organisation, 2022).

Symptoms of hepatitis A range from mild to severe and can include fever, malaise, loss of appetite, diarrhoea, nausea, abdominal discomfort, dark-coloured urine and jaundice (a yellowing of the eyes and skin) (World Health Organisation, 2022).

Improved sanitation, food safety and immunization are the most effective ways to combat hepatitis A. The spread of hepatitis A can be reduced by adequate supplies of safe drinking water; proper disposal of sewage within communities; and personal hygiene practices such as regular handwashing before meals and after going to the bathroom (World Health Organisation, 2022).

A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host. There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites (CDC, 2022).

A wide variety of helminthic roundworms, tapeworms, and flukes are transmitted in foods such as undercooked fish, crabs, and molluscs; undercooked meat; raw aquatic plants, such as watercress; and raw vegetables that have been contaminated by human or animal faeces (CDC, 2021).

Symptoms of foodborne parasitic infections vary greatly depending on the type of parasite (diarrhoea, abdominal pain, muscle pain, cough, skin lesions, malnutrition, weight loss, neurological, etc.) (CDC, 2021).

Guidance on the prevention of parasites: thoroughly washing, peeling and cooking food such as vegetables or fruits; boiling water to kill the parasite (Cleveland Clinic, 2019); do not use raw or undercooked oysters, mussels, or clams; do not use unpasteurized goat’s milk; cooking food to safe temperatures (for whole cuts of meat (excluding poultry) cooking temperature is at least 63° C, for ground meat (excluding poultry) cooking temperature is at least 71° C, for all poultry cooking temperature is at least 74° C) (CDC, 2022); washing hands often; only drinking from safe water sources (Cleveland Clinic, 2020).