Why is South Africa experiencing the deadliest outbreak of listeriosis? That’s a question that local residents and health authorities have been trying to understand over the last few months, to no avail.
As the death toll rises to at least 82, the cause of the outbreak remains unknown, meaning there can be no definitive way to avoid infection.
Spread of the infection
The average number of reported and treated cases of listeriosis in South Africa every year is between 60 and 80. But Minister of Health Dr Aaron Motsoaledi suggested the unusually high number of infected babies sparked doctors in Chris Hani Baragwanath and Steve Biko Academic hospitals to alert the National Institute for Communicable Diseases (NICD) in July 2017.
In early December 2017, the Department of Health made listeriosis a notifiable disease, which means a diagnosed patient must be reported. This helped track the number of cases and the development of the outbreak.
Of the 557 laboratory-confirmed listeriosis cases reported between 1 January and 29 November 2017, the Gauteng, Western Cape and KwaZulu-Natal provinces were responsible for 82%.
An update from the NICD stated that as of 23 January 2018, the number of reported cases jumped to 820. The Guateng province had the highest proportion of cases at 59%, followed by 13% in Western Cape and 7% in KwaZulu-Natal.
Both private and public health facilities had diagnosed cases, which led Motsoaledi to infer: “The source of the outbreak is likely to be a food product that is widely distributed and consumed by people across all socioeconomic groups.”
The fatality statistics are not conclusive as outcome data is only available for 238 of the 820 cases. This data revealed that 82 people (34%) have died so far as a result of infection. However, foodborne illnesses are not the usual cause of death in South Africa, with tuberculosis far more likely at 8.8%, and HIV/AIDS 5.1%.
The South African outbreak of listeriosis is the largest ever reported, overtaking the United States outbreak in 2011, and Italy in 1997.
Affecting over 1500 people, the majority of whom were children at two schools, the source of the Italian outbreak was cold corn and tuna salad. The US outbreak, on the other hand, was caused by rockmelons from Jensen Farms in Colorado, which infected 147 people and killed 33.
Cause remains unknown
So what is the source of the South African outbreak? The simple answer is, it remains a mystery.
Although there are 17 strains of the organism, not all of them are disease-causing. Authorities are trying to establish which strain (or strains) may be responsible and where it comes from.
The NICD reported that of the 247 clinical isolates that were sequenced by the end of December 2017, 91% were sequence type 6 (ST6) and are very closely related, which indicates it could be a single strain of the bacterium Listeria monocytogenes.
“This ST6 strain has been identified in isolates from all nine provinces, and this finding supports the current working hypothesis of a single source of food contamination causing the outbreak, i.e. a single widely consumed food product, or multiple food products produced at a single facility,” the NICD report explained.
A food outlet in the City of Johannesburg was suspected to be a potential source of infection, according to Member of the Mayoral Committee (MMC) for Health and Social Development Dr Mpho Phalatse.
While the outlet was not named, samples were taken to the NICD for testing in mid-January 2018.
“We are awaiting lab confirmation of whether or not this is a disease-causing strain of the organism,” said Phalatse.
Strategic Advisor in the office of the MMC Dominic Mahlangu explained: “Steps are being taken to sterilise the area. We do not want the business to suffer serious damage and we do not want to spread panic.”
However, the numbers of infected have continued to rise and the NICD have not yet provided confirmation, which suggests this was not the source.
What is listeriosis?
With cases of listeriosis have been flooding headlines recently, and the outbreak in South Africa escalating, it is more important than ever to understand what it is, who is at risk and how you can get it.
Listeriosis is a disease caused by the bacterium Listeria monocytogenes, which is transmitted to people through contaminated food. It is often found in soil, water and vegetation, meaning it can contaminate animal products such as raw meat, seafood and dairy products, as well as unwashed vegetables.
For this reason, potential sources have been identified as farms, food processing plants, retail outlets and food preparation at home.
While anybody can become infected, healthy individuals tend to experience symptoms including diarrhoea, fever, general body pains, vomiting and weakness. In more severe cases, it has been known to cause meningitis, bacteria in the blood and complications in pregnancy, including miscarriages and premature birth.
Christian Lindmeier, spokesperson for the World Health Organization (WHO), explained that pregnant women “are 20 times more likely to get listeriosis than other healthy adults” and “newborns are about 40% of the infected people”.
Others who are particularly at risk include the elderly and those with compromised immune systems.
Since there can be up to a 70-day incubation period between exposure and symptoms, it is particularly difficult to establish the source.
Can you recall exactly what you ate over the last two months? From the garnishes on a plate in a restaurant to where you bought your vegetables, pinpointing the origins of the outbreak can be a monumental task. As Lindmeier noted, “You wouldn’t know what you ate three weeks ago — maybe the one particular food that made you sick three or four weeks later — this is the big challenge we face in this situation.”
Taking into account the incubation period, the number of those infected in South Africa is likely to continue to rise as more people report having symptoms.
Lindmeier suggested a collaborative effort between the health, food and farming sectors is now required to tackle the outbreak. The NICD is working alongside the National Department of Health and the Department of Agriculture, Forestry and Fisheries to investigate the source.
In a statement, the NICD said:
“The National Department of Health is co-ordinating a multi-sectoral response with all agencies within government. We are firstly interviewing all persons who have been diagnosed with Listeria to understand what food they have eaten, and identify trends. Secondly, we are working with the food safety and quality industry to obtain quality data from food control and to sample food production facilities. Thirdly, we have worked with infectious diseases physicians to draw up guidelines for diagnosing and treating the disease. Fourthly, we are working with health promotion to increase awareness of how to prevent listeriosis. Presently no food sources that are contaminated with the outbreak strain have been found, including amongst poultry and poultry products.”
While the investigation is ongoing, WHO suggested the best preventative measure is to educate the public and those who supply and handle food on how to maintain food safety. These include: washing your hands before, during and after handling food; separating raw and cooked foods; cooking food thoroughly; keeping food at the correct temperature, such as storing it in the fridge; and using safe, clean water and pasteurised milk products.
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