Source Identified for the Deadliest Listeria Outbreak in History


South Africa has experienced 978 lab-confirmed cases of listeria poisoning since January 2017 [1], in what the United Nations has declared the largest listeria outbreak ever [2]. In total, the listeria outbreak has killed 189 people [3]. The provinces most affected include Gauteng, the most densely populated province which accounts for 59% of reported cases, and Western Cape with 12% of cases [4].


After a year of tracing the outbreak, health officials have concluded that the source of the outbreak originated in a factory in Polokwane, that makes Enterprise Food products. An RCL plant that makes similar products is also under investigation [5].  A shortage of the solution used to test for the presence of listeria caused a delay in results declaring the source of the outbreak as the Polokwane factory by two weeks [6]. An international recall of the sausage polony  produced by the factory was issued, as the specific type of processed meat is suspected to be the root cause of the outbreak. South Africans have also been advised to refrain from eating any type of processed meat, as cross-contamination may have occurred at any stage of production or distribution [6].


In an attempt to improve surveillance, the South Africa Department of Health added listeriosis as a notifiable condition as of December 2017 [4]. Listeriosis infection can develop after eating food contaminated with the bacterium Listeria monocytogenes [7]. Symptoms include fever and diarrhea, headache, stiff neck, confusion, and convulsions. Those particularly at risk are the elderly, infants, and pregnant women, who can pass the infection onto the fetus. Infections during pregnancy can also lead to miscarriage, stillbirth or premature delivery [8]. Approximately 42% of the cases in the current outbreak were newborns [3]. Due to the delayed implementation of listeriosis as a notifiable condition, and the typical under-reporting of foodborne illness, the reported number of cases is likely a significant underestimate of the actual magnitude of the outbreak.


While the outbreak was originally contained to South Africa, it is now threatening other countries. The World Health Organization (WHO) is providing support for preparedness and response to 16 additional African nations who are at heightened risk for having the outbreak spread across their borders [9]. The meat products connected to the outbreak have been exported to two West African countries and 14 members of the Southern African Development Community, an intergovernmental partnership. Namibia has reported one confirmed case of listeriosis, which occurred in early March 2018. An investigation is currently ongoing to see if the case is connected to the outbreak in South Africa [9]. Due to the long incubation period of the listeriosis, which can be up to 70 days, more cases are likely to emerge. Additionally, health officials reported that 9% of cases involved a different strain of listeria, indicating that multiple outbreaks may be occurring simultaneously [3]. Listeriosis is not currently a notifiable priority disease among countries and member states in the African Region, as defined by World Health Organization (WHO) technical guidelines [10]. However, due to the outbreak in South Africa, the WHO is encouraging health officials in surrounding countries to report any new cases of listeriosis [1].


This outbreak has far surpassed any other listeria outbreak in history; the next largest documented listeria outbreak occurred in the United States in 2011, with 147 cases in total, which was linked to cantaloupes [11]. Improved surveillance is critical to prevent additional surrounding countries from experiencing outbreaks of similar size.





















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