Food-borne diseases are those diseases acquired after ingesting contaminated food. They can be caused by several microorganisms. The most important bacterial agents are Enterobacteriaceae. However, most bacteria do not grow optimally under refrigeration temperatures. For this reason, most foods are stored under refrigeration to significantly reduce or inhibit the growth of some bacteria. However, some bacteria can continue to grow under these conditions. The most notable bacteria that grow in refrigerated food are Listeria monocytogenes and some strains of some enterobacteria.
Other bacteria that may contaminate chilled food include Escherichia coli, Bacillus cereus Clostridium botulinum, and clostridium perfringens. Bacillus cereus produces heat-resistant spores which are responsible for food poisoning. Refrigeration does not eliminate viruses and it has been argued that refrigeration or chilling can preserve viruses. A wide range of viruses can survive in very low temperatures.
Some become dormant and they are reactivated upon exposure to the right temperatures. Viruses most commonly associated with food poisoning are noroviruses, rotaviruses, and hepatitis A virus. However, viruses are destroyed by heat. Contamination of ready-to-eat food occurs after cooking. Poor handling of cooked food and cross-contamination can introduce microorganisms into a food. This paper will discuss the causes, epidemiology, and preventive measures of food-borne illnesses.
Listeria monocytogenes is a Gram-positive motile bacillus. It rarely causes disease in adults of sound immunity. It is mainly associated with infections in infants, pregnant women, the elderly, and adults with compromised immunity. The disease it causes is called listeriosis. The number of cases reported is small but of primary concern is the number of deaths it causes in the vulnerable group. Listeria oncogenes are widely present in nature. Infection with it is associated with the consumption of contaminated food products (Finlay, 2001). Food products that have been implicated include soft cheeses, fruits, vegetables, and seafood.
In 1985 142 cases of listeriosis were reported out of which 48 died from the disease in the California United States of America (ICMSF 1996). The incidence of listeriosis lies between 2% and 16% per 1000, 000(Cabanes et al. 2002). Cabanes et al. (2002) reported that the death rate of listeriosis is above 20 %. In the United States, the incidence was 3 cases per million in the year 2004/2005. About 30%of the cases were pregnant women. Incidence in the United States has been dropping while that of Europe has been rising in the recent past. In the United States of America, approximately 2500 persons become ill with listeriosis each year. Of these 500 die (Mead et al 1999).
Table 1: The number of confirmed cases in Europe in 1999 to 2006(Denny J, McLauchlin J. 2008)
Table 1 shows an upward trend in the number of confirmed cases in several European countries. Some countries which high numbers of infections include Ireland, Lithuania, the Netherlands, Spain, the UK, and Germany.
Infection with listeria monoctogenes causes listeriosis. The infection can invasive or noninvasive. Following infection with the bacteria, the signs and symptoms that can be noted include meningitis, septicemia, pneumonia, corneal ulceration, spontaneous abortion in pregnant women, and encephalitis. These symptoms are preceded by a low-grade fever. After infection, the symptoms may appear within 12 hours or delay up to three weeks.
The infective dose of Listeria monocytogenes is thought to be less than 1000 organisms in the susceptible host. Listeria monocytes express D-galactose residues on their surface. These molecules can attach to D-galactose receptors on the host cells. These receptors are primarily concentrated in the intestinal wall, blood-brain barrier, and fetoplacental barrier. The adhesion molecule is thought to be a protein called internalin. After attachment to the receptor, it is transported into the body. It enters the human macrophages and polymorphonuclear leukocytes where it grows and multiplies.
Improper refrigeration can lead to infection with spore-forming bacteria like Bacillus cereus and toxin-producing bacteria like Clostridium perfringens and Clostridium botulinum. Spore may continue to germinate in improperly refrigerated foods. Some toxins are heat resistant and cooking does not deactivate them. When ingested in food, the toxins cause several symptoms including vomiting and diarrhea. Bacillus cereus leads to a mild, self-limiting illness. Infection with Bacillus cereus has no geographic distribution periodicity (Shapiro et al, 1999, p. 610)
Several measures can be taken to avoid infection with food-borne microorganisms. The preventive measures can be divided into two categories; those that target the general public and those that target the vulnerable groups.
General recommendations
- Maintain high standards of hygiene. To avoid contaminating food with bacteria during handling it is important to maintain a high standard of hygiene. Measures that should be put in place to ensure no contamination occurs include washing hands thoroughly with warm soapy water before and after handling food. Hands should be dried using a dry hand towel. Hand towels should be changed daily. After cooking the utensils should wash thoroughly before drying and storing them safely. Cutting boards and knives should be given particular attention. Clean all the areas that have been in contact with raw animal products like meat, poultry, and pork. Any juices or spills from these products should be thoroughly cleaned. The inside of the fridge or freezer should be cleaned well with hot water and detergent. It is also important t keep the general cooking environment clean and safe (CDC n.d).
- Wash raw food well. All foods that are eaten raw should be cleaned thoroughly before eating. Clean vegetables and fruits with a kitchen raw produce brush. After cleaning the vegetables and fruits rinse the brush and dry it well before keeping it safe. It is important to remember that all raw food should be washed thoroughly before embarking on any other process like cooking. All washed produce should be dried using a clean dry kitchen towel. Avoid using the hand towel to dry food.
- Proper cooking. All animal products must be cooked to the right internal temperature before serving or chilling. This ensures that all the heat-sensitive microorganisms are killed. When reheating food make sure that it is stirred well to ensure even distribution of heat.
- Refrigeration. Refrigerate food at the right temperature. Raw food like meat and chicken should be kept below the cooked food in the refrigerator. Never mix them or store raw food above cooked ready-to-eat food. This is aids in preventing cross-contamination.
- Safe storage. Packed food should not be stored for long once they have opened. Foods that have been repacked by the seller should generally be used immediately. Do not store pre-cooked food for long before using it. Food should be eaten immediately after cooking if it cannot be refrigerated or frozen. Cover all food that has been left standing to avoid contamination.
Recommendations for persons at particular
This group of individuals includes pregnant women, elderly people, children, and people who are immunocompromised.
- Do not eat meat, pork, poultry, and sausages that have not been cooked properly. Ensure that these foods are cooked until steaming hot before eating them. Any animal product that has been repackaged by a local seller should be avoided as it may have been contaminated during repacking. Fresh cut meat should be used cautiously.
- Soft cheeses like pate should be avoided.
- Juices from raw products should not come in contact with cooked food. Wash hands thoroughly after touching raw food. Hands should be dried after cleaning to further reduce the chance of contamination.
- Pay attention to product labels. Do not eat food whose sell-by dates have expired. Food that has been stored for a long may have been overgrown by bacteria.
- Chilled smoked fish should be avoided.
- Fruits and any other food is eaten raw should be thoroughly washed before eating.
- Discard all food that has been left standing for long.
- The overall hygiene of food handlers, working surfaces, and utensils should be kept high. (Finlay, 2001, p. 1666)
In conclusion, bacteria that may cause food-borne illnesses are diverse. Enterobacteria are the commonest causes of bacterial poisoning. Viruses can cause food poisoning but they are inactivated by heat. The commonest enteric viruses are noroviruses and hepatitis A viruses. The commonest bacterial agent associated with cooked ready-to-eat food is Listeria monoytogenes.it is a gram-negative motile rod found in soil and animals. It causes listeriosis, an illness that is characterized by meningitis, pneumonia, encephalitis, and uterine infections. Its pathogenicity is attributed to adhesion molecules found on its surface.
It can infect anybody but some people are at an increased risk. Its incidence has been declining in the United States of America in the recent past while that of Europe appears to be going up. People with more than average risk include pregnant women, infants, elderly people, and immunosuppressed people. Control measures include maintaining high standards of hygiene, avoiding consumption of undercooked food, and washing raw foods well before eating.
References
Cabanes, D., Dehoux, P., Dussurget, O., Frangeul, L., Cossart, P. ” Surface proteins and the pathogenic potential of Listeria Monocytogenes”’ Trends Microbiol., 10, 238–245.
Center for Disease Control and Prevention n.d, “Listeriosis”. Web.
Denny, J. and McLauchlin, J, “Human Listeria monocytogenes infections in Europe – an opportunity for improved European surveillance”, Euro Surveill. 2008; 13vol. 13. Web.
Finlay’ B, 2001, “Cracking Listeria’s password”’, Science 292, 1665–1667.
ICMSF, 1996, Microorganisms in Foods 5, “Characteristics of Microbial Pathogens Listeria monocytogenes”, Blackie Academic & Professional, London, pp. 141–182.
Shapiro, C., Griffin, P.M., Tauxe, V., 1999, “Food-related illness and death in the United States”, Emerg. Infect. Dis, 5, 607–625.