In recent years, multiple outbreaks of foodborne illness caused by the deadly pathogen Listeria monocytogenes (Listeria) have been linked to thousands of illnesses and hundreds of deaths.
In 2024, at least 61 people were sickened and ten people died in an outbreak of Listeria connected to contaminated Boar’s Head deli meats. Just last week, the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control (CDC) announced that they had closed their investigation into yet another deadly Listeria outbreak linked to frozen nutritional shakes served in long-term care facilities and nursing homes. Although the outbreak has now been declared to be over, 42 people were sickened and 14 people died.
While both of those incidents sickened over 100 people in the United States, a 2017–2018 outbreak of Listeria in South Africa was the largest and deadliest recorded globally, with 1,060 confirmed cases and 216 deaths reported between January 2017 and July 2018. The outbreak was caused by Listeria monocytogenes sequence type 6 (ST6), a bacterial strain linked to ready-to-eat processed meat products, particularly polony (a bologna-like sausage), produced at the Enterprise Foods facility in Polokwane, a subsidiary of Tiger Brands. This marked South Africa’s first major listeriosis crisis, as the country previously reported only 60–80 annual cases.
The outbreak was first detected in July 2017 when doctors noted an unusual surge in neonatal infections at hospitals in Gauteng Province. By mid-2018, cases had spread nationwide, with 58% occurring in Gauteng, 13% in the Western Cape, and 7% in KwaZulu-Natal. Neonates accounted for 42% of cases, primarily due to vertical transmission from infected pregnant mothers, while immunocompromised individuals, the elderly, and pregnant women faced the highest mortality risk. The case fatality rate was approximately 27%, consistent with global listeriosis outbreaks.
Whole-genome sequencing (WGS) played a pivotal role in tracing the source. Analysis revealed that 91% of clinical isolates were ST6, which matched strains found in environmental swabs and polony samples from the Enterprise Foods facility. Single nucleotide polymorphism (SNP) comparisons showed fewer than 10 genetic differences between clinical and factory-derived ST6 isolates, confirming epidemiological links. Investigations also identified non-ST6 strains in 9% of cases, suggesting concurrent smaller outbreaks.
On March 4, 2018, South Africa’s health ministry announced the outbreak’s source and initiated a nationwide recall of Enterprise Foods products. Over 12,000 tons of contaminated food were destroyed, and 15 African countries suspended imports of South African processed meats. Tiger Brands faced significant financial losses, including a 7% stock drop and a class-action lawsuit representing approximately 1,000 claimants.
The outbreak exposed gaps in South Africa’s food safety systems, including fragmented regulations and a lack of standardized Listeria monitoring in food production. In response, listeriosis was declared a notifiable disease, and food safety laws were updated to mandate hazard analysis and critical control point (HACCP) systems for ready-to-eat meat producers. Nearly 900 health inspectors were retrained, and enhanced surveillance protocols were implemented with support from the World Health Organization (WHO).
The outbreak was declared over in September 2018 after three months without new ST6 cases. However, the exact route of ST6 contamination at the Enterprise facility remains unresolved. The crisis was yet another critical example of the importance of robust food safety infrastructure, rapid genomic surveillance, and international collaboration in managing foodborne disease outbreaks.
