Listeria-contaminated food and listeriosis
Listeria-contaminated food is the main cause of listeriosis, a condition that can develop. A rod-shaped, gram-positive form of Listeria bacteria called Listeria monocytogenes is what causes the infection. The human central nervous system is particularly susceptible to the bacterium. The ideal temperature for cell division is 37 °C, although the infectious species can live in temperatures as low as -7 °C and as high as 45 °C. Once food is contaminated with Listeria monocytogenes, the bacteria can continue to reproduce even in refrigerated food due to their capacity to multiply at low temperatures of 0°C. The bacteria can also survive in a wide range of pH conditions and salt concentration making it thrive in almost all environmental conditions (Painter & Slutsker, 2009). However, simple cooking of food can kill the bacteria as it cannot survive temperatures beyond 45°C. This essay looks into the epidemiology of the bacterial infection in humans and recommends preventive measures to prevent infection with the disease.
Listeriosis Epidemiology
Transmission of Listeria monocytogenes
Outbreaks of Listeriosis has been linked with intake of contaminated food in ready-to-eat packed food, vegetable, and contaminated milk. The may get contaminated during preparation, and the bacteria multiply when the food is in storage. The bacteria are dispersed in a variety of the natural environment including water, soil and rotting vegetation (Swami & Gerner, 2007). Domestic animals are a common reservoir for the bacteria. Neonatal transmission is also common for infected pregnant mothers where the pathogen infects the fetus through the placenta. Also, contaminated equipment during delivery of the child can lead to the infection of both the mother and the child. The principal route for infection is, however, the oral-fecal channel.
Incubation Period and Susceptible groups
The incubation period for the pathogen ranges from 3-70 days upon exposure to the contaminated food. Once ingested, the bacteria travel from the stomach to the blood across the epithelium layer of the small intestines and spreads to the spleen, liver and the central nervous system (Painter & Slutsker, 2009). It can also reach the fetus through placenta for pregnant women. The most susceptible groups can be categorized into three main groups according to the predisposing factors. Pregnant women are thought to be at a higher risk of infection due to decline in their immunity during the pregnancy. Newborns are also more likely to be infected with listeriosis due to prematurity, which is characterized by low immunity too. The elderly beyond 65 years of age are also at a higher risk of infection due to suppression of their immunity, weakness brought by liver cirrhosis for the alcoholics, diabetes and general reduction of their immunity against infection in the advanced age (Varna, Samuel, & Marcus, 2007)
Signs and symptoms
Since the disease attacks, central nervous system and soft tissues such as the lymphatic systems, liver and spleen, signs associated with the infection of these tissues are the most conspicuous of the infection with listeriosis. A severe headache, fever, vomiting, and nausea are preceding meningitis in the elderly. Patients with cardiac lesions also exhibit endocarditis. Flu-like infection is common in pregnant women, and incidences of stillbirth or abortion have been reported. Sepsis, pneumonia, and meningitis are common neonates with infrequent cases of granulomatosis infantiseptica that is characterized by the occurrence of abscesses in the internal organs (Department of Health Hong Kong , 2007).
Clinical Diagnosis
The laboratory diagnosis can be confirmed by the isolation of the bacteria from a specimen taken from the pericardial fluid, blood, amniotic fluid, fetal tissue, placenta or cerebrospinal fluid. After the isolation of the Listeria genome, the Listeria monocytogene has to be positively identified from other gram-positive bacilli (Painter & Slutsker, 2009). Once the specimen is enriched for Listeria spp., it is placed in a Listeria-selective medium and typing such as serotyping use to isolate the Listeria monocytogene from the rest of the genomes. Pulsed-field gel electrophoresis can also be used to isolate the causative agent of the disease in a clinical specimen. In the case of non-culture tests, microscopic examination to check the presence of gram-positive rods can be used for presumptive diagnosis.
Treatment and control of infection transmission
Antibiotics are used to treat the infection. Treatment with penicillin min combination with an aminoglycoside for at least a two weeks duration has been found to be effective for mild infections. Severe cases involving incidences of abscesses, cerebritis, and patients with a compromised immune system can take longer to effectively treat (Swami & Gerner, 2007). Handling of the excretion and body fluids for care-givers of the patients should follow standard precautions to prevent the spread of the infection. Decontamination of the equipment at the hospital should also be properly done.
A Case Study involving Listeriosis Epidemiology
The presence of Listeria monocytogenes in smoked seafood with finfish being of particular interest for the WHO draft paper 2010 that investigated the incidence (Buchanan, Whiting, & Ross, 2010). The study focused on the prevalence of contamination of food products in the packaging and food processing industry. This was of importance for public health owing to the ubiquity of the bacteria to survive in refrigerated temperature, resistance to acidic and high salt level, making the bacterial species survive in the prolonged shelf life of the smoked seafood products. In this survey, it was observed that the bacteria are capable of surviving in smoked foods due to its resistance to relative heating. This resulted from samples with an extraordinarily high level of the bacteria. Adequate heat treatment in the hot-smoked seafood was observed eliminate the incidence of bacteria. However, the contamination in the subsequent stages of packaging presented the highest chance of contamination of the food. The packaging of cold-smoked salmon was observed to have a higher incidence of contamination. However, in the production process, stringent measures have been put in place to reduce such cases. These include observance of hygiene in handling the product in the last stages of the packaging process (Buchanan, Whiting, & Ross, 2010).
Conclusion
From the preceding, it has been established that the causative agent for listeriosis is the facultative anaerobic gram-positive, rod-shaped Listeria monocytogenes bacteria that attacks the nervous system and the soft tissues such as the liver and spleen. The most common mode of transmission is through ingestion of contaminated food. The most susceptible population are those suffering from diseases suppressing the immune system, the elderly, infants and pregnant women who can transmit the disease to the fetus. Common symptoms are severe headaches, fever, nausea, and meningitis. Infection can also result in abortion for pregnant women. Diagnosis involves isolation of the Listeria monocytogenes species of the bacteria from a culture specimen through field gel electrophoresis or serotyping. Microscopic evaluation of blood, amniotic fluid or any other body fluid may also be used to identify the rod-shaped, gram-positive bacteria. Treatment with antibiotics such as penicillin is the most common form of treatment with careful handling of body fluids from infected persons being used to prevent transmission of the infection.
Reference
Buchanan, R., Whiting, R., & Ross, T. (2010). Case Study: Listeria monocytogenes in Smoked Fish: Development of Risk Management Metrics for Food Safety. Geneva: Department of Food Safety, Zoonosis, and Foodborne Diseases WHO.
Department of Health Hong Kong. (2007). Scientific Committee on Enteric Infections and Foodborne Disease: Epidemiology of Listeriosis and Prevention Strategies. Victoria City: Hong Kong Center for Health Protection.
Painter, J., & Slutsker, L. (2009). Listeriosis in Humans. In E. Ryser, & h. E. Mart, Listeria, listeriosis, and food safety (pp. 85-109). London: CRC Press.
Swami Nathan, B., & Gerner-Smidt, P. (2007). The epidemiology of human listeriosis. Microbes and infection, 236-243.
Varma, J. K., Samuel, M. C., & Marcus, R. (2007). Listeria monocytogenes Infection from Foods Prepared in a Commercial Establishment: A Case-Control Study of Potential Sources of Sporadic Illness in the United States. Clinical Infectious Diseases, 521-528.
