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Public Health Approach to Listeria monocytogenes
Background South Africa currently faces a serious listeriosis outbreak which the World Health Organisation has identified as the worst in the world. The South African Medical Association is concerned by the current outbreak, and supports all legislative and policy measures aimed at protecting the public’s health from the threat of listeriosis.
Foodborne diseases are among the most widespread public health challenges globally[1], with foodborne listeriosis being one of them.
Listeriosis is an infectious, rare yet severe, disease caused by a gram-positive bacterium called Listeria monocytogenes (L. monocytogenes) that can penetrate and replicate inside human cells. The most common habitats of L. monocytogenes are soil and water, from which the pathogen is transmitted to plants, animals, and the food chain. Listeriosis is a serious, but preventable and treatable disease
Except for mother to child transmission, there is no human to human listeriosis transmission, as the disease is spread to humans mainly by contaminated food or fluids. Contaminated raw food (such as fruits, vegetables, meat, cheese, unpasteurized milk) and ready-to-eat (RTE) foods are the major source of human listeriosis cases[2].
The incubation period of Listeria monocytogenes is 3 – 70 days (mean 31 days) days after a single exposure to an implicated product [3].
Particularly susceptible to L. monocytogenes infection are neonates ≤ 28 days, the elderly above 65 years, pregnant women, and any persons with weak immunity such as HIV, diabetes, cancer, chronic liver or kidney disease patients. In pregnant women, the infection can result in miscarriage, premature delivery, serious infection of the new-born, or even stillbirth.
Typical symptoms include fever, muscle aches, nausea, or diarrhoea. If infection spreads to the central nervous system, symptoms can include headache, stiff neck, confusion, loss of balance, and convulsions.
A most unique feature of L. monocytogenes is its ability to survive and multiply in a broad range of environmental conditions typically used in food preservation, such as low pH, refrigeration temperatures, and high salt concertation.
Before the outbreak, South Africa has had clinical guidelines on “the management and control of infectious foodborne diseases in South Africa, 2011”[4]. South Africa’s multi sectoral team responding to the outbreak are: The Department of Health, World Health Organisation, the National Institute for Communicable Diseases (NICD), Department of Trade and Industry (DTI), Department of Agriculture, Forestry and Fisheries (DAFF); National Consumer Commission (NCC); National Regulator for Compulsory Specifications (NRCS), the Consumer Goods Protection of South Africa; and the Media.
Listeriosis Outbreak History: Local and Global
Listeriosis has been recognised as a human disease since the 1930s. Prior to the current listeriosis outbreak, the world’s largest listeriosis outbreaks were in the United States in 2011 and in Italy in 1997[5].Laboratory records indicate that sporadic cases of listeriosis occur in South Africa with approximately thirty to sixty laboratory-confirmed cases diagnosed annually[3].
Listeriosis Epidemiologic Triangle
The Epidemiologic Triangle, depicted below, is a model that scientists have developed for studying health problems, specifically to investigate how a disease spreads and how to combat it. The epidemiologic triangle is made up of three parts: agent, host and environment. Control and prevention measures aim to break the epidemic/epidemiological triangle/cycle of Listeriosis by addressing one or all of the three nodes of the triangle.
Agent:
The bacterium L. Monocytogenes
[most importantly sequence type 6 (ST6)]
Host:
Age, low immunity, food handling & hygiene
behaviour, socioeconomic factors
Environment:
Food, water, soil, human
body, animal body, (temperature, pH, nutrient availability,
moisture, time), access to healthcare,
Public Health Approach to Listeriosis
South Africa’s response, thus far, to the current listeriosis outbreak conforms to the public health approach in many respects.
Beginning some years back, the World Health Organisation (WHO) has been adopting a public health approach, supported by a strong evidence base, to control various diseases and outbreaks in certain countries or contexts. The public health approach is a systematic process that is most instrumental in resource-poor settings and is aimed at improving the accessibility and quality of individual and population based health services.
Concomitant with the public health approach, the South African Department of Health emphasizes the importance of multidisciplinary and multisectoral collaboration, particularly in policy development and implementation of strategies for controlling communicable diseases[4]
I. Surveillance (What is the Problem?)
In July 2017, doctors from neonatal units at Chris Hani Baragwanath and Steve Biko Academic Hospitals noticed an unusually high numbers of neonatal cases of Listeriosis, to which they alerted the National Institute of Communicable Diseases (NICD). The majority of cases were reported initially in one province (Gauteng), and the source of the L. monocytogenes was then unknown. To date, all nine provinces have reported cases, although the highest incidence is still in Gauteng province. As of 8 March 2018, 967 laboratory-confirmed listeriosis cases have been reported to NICD from all provinces since 01 January 2017 (Figure 1 and Table 1). The currently reported case fatality rate for listeriosis, based on the 663 cases with known outcome ant the 183 listeriosis –associated deaths, is 27%
Figure 1: Epidemic curve of laboratory-confirmed listeriosis cases by epidemiological week and date of sample collection and province, South Africa, 01 January 2017 to 8 March 2018 (n=967)
1.Number of cases keep changing by the day, affecting the numerator and the denominator
Table 1 Outcome of 967 persons with laboratory-confirmed listeriosis by province, at 8 March 2018
II. Risk Factor Identification (What is the cause?)
To drill to the bottom of the outbreak, South African health experts applied the observation that listeriosis cases were reported in both the public and private health sectors, generating the theory that the disease is most likely spread by a commonly consumed foodstuff originating from a single source. Following this lead, a rigorous process of investigation was instituted, involved a multisectoral set of experts. The process involved:
• Visits by health experts to various sites in the food value chain
• Taking food samples from meat manufacturing plants and retail shops
• Interviewing individuals about food consumption
• Taking and testing stools samples from suspected cases
• Laboratory tests on clinical isolates obtained from patients
• Whole genome sequencing analysis for laboratory confirmation was performed focusing on a particular factor (Enterprise food production factory) in Limpopo.
Based on the above the Health officials concluded that the consumption of ready-to-eat processed meat products was the risk factor. The consumption of foods refrigerated for prolonged periods add another layer of risk because L. monocytogenes survives under fridge temperatures, and also the risk of cross- contamination of other refrigerated foods in retail shops and homes.
III. Intervention Evaluation (What works?)
The South African government and stakeholders considered Prevention (both primary and secondary) as a high priority option for the control of the listeriosis outbreak.
IV. Implementation (How do you do it?)
The government took the following measures to eliminate or reduce some of the aspects of the epidemiologic triad:
• listeriosis was made a notifiable disease starting December 2017.
• Provision of clinical management guidelines for listeriosis
• Safety recall issued to implicated food manufacturer, which extends to retail shops and the entire value chain.
• Regular situation reports by the NICD and the DoH(e.g. Media briefing)
• The Government continues to urge health care workers to maintain vigilance for new cases.
• Public education (via Press, Radio, Websites, social media) on the WHO advocated five food-safety rules . • Identifying provincial capacity gaps and and ameliorative steps
Conclusion
Although the identification of the source of L. monocytogenes is a huge milestone in containing the outbreak, the impact of the public health approach applied to date, although quite impressive, is undercut by lack of enforcement, as the implicated food products are still found in retail shops.
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2.Keep clean; separate raw and cooked foods; cook thoroughly; keep food at safe temperatures; use safe water and raw materials
3.Minister of Health has promised to change the Constitution in order to take away from local authorities the management of Environmental Health Practitioners
References
1. Pal M, Ayele, Y. Kundu, P. Jadhav, VJ. Growing imprtance of listeriosis as foodborne disease. journal of experimental food Chemistry, 2017. 3.4.
2. Pradhan K, A.Ivanek, R. Grohn, T. Comparison of public health impact of listeria monocytogenes product to product and environment to product contamination of Deli meats in retail. Journal of food protection, 2011. 74.
3. National Institute for Communicable Diseases (NICD)
4. Department of Health South Africa, Clinical Guidelines on the management and control of infectious foodborne diseases in South Africa, 2011. 2011.
5. World Health Organisation
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