SA’s listeriosis outbreak fuelled by HIV and lack of awareness

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The listeriosis outbreak that killed more than 200 people in South Africa between 2017 and 2018 was fuelled by HIV and a lack of awareness of the risks of eating deli meat in pregnancy. Business Day reports that this is according research by scientists who analysed 937 cases of listeriosis confirmed between June 2017 and April 2018. More than 400 cases occurred among newborn babies, and 59 of the cases were pregnant women or girls. Among the patients whose HIV status was known (415), almost 42% (174) were positive.

The source of the disease was eventually traced to polony made in a factory operated by Enterprise Foods, which is owned by South Africa’s biggest food producer, Tiger Brands.

“The size and velocity of the outbreak were noteworthy and most likely resulted from the wide distribution of large volumes of contaminated products in a large population vulnerable to invasive listeriosis,” wrote the researchers led by Juno Thomas, from the National Institutes of Communicable Diseases.

South Africa has the world’s biggest HIV epidemic, with more than 7.7m people living with the disease, according to UNAIDS. The authors said the number of patients with pregnancy-related listeriosis was probably an underestimate, as mild cases might have gone undetected. They called for better health communication about the dangers of listeriosis to pregnant women and people with HIV.

Abstract
Background: An outbreak of listeriosis was identified in South Africa in 2017. The source was unknown.
Methods: We conducted epidemiologic, trace-back, and environmental investigations and used whole-genome sequencing to type Listeria monocytogenes isolates. A case was defined as laboratory-confirmed L. monocytogenes infection during the period from June 11, 2017, to April 7, 2018.

Results: A total of 937 cases were identified, of which 465 (50%) were associated with pregnancy; 406 of the pregnancy-associated cases (87%) occurred in neonates. Of the 937 cases, 229 (24%) occurred in patients 15 to 49 years of age (excluding those who were pregnant). Among the patients in whom human immunodeficiency virus (HIV) status was known, 38% of those with pregnancy-associated cases (77 of 204) and 46% of the remaining patients (97 of 211) were infected with HIV. Among 728 patients with a known outcome, 193 (27%) died. Clinical isolates from 609 patients were sequenced, and 567 (93%) were identified as sequence type 6 (ST6). In a case–control analysis, patients with ST6 infections were more likely to have eaten polony (a ready-to-eat processed meat) than those with non-ST6 infections (odds ratio, 8.55; 95% confidence interval, 1.66 to 43.35). Polony and environmental samples also yielded ST6 isolates, which, together with the isolates from the patients, belonged to the same core-genome multilocus sequence typing cluster with no more than 4 allelic differences; these findings showed that polony produced at a single facility was the outbreak source. A recall of ready-to-eat processed meat products from this facility was associated with a rapid decline in the incidence of L. monocytogenes ST6 infections.
Conclusions: This investigation showed that in a middle-income country with a high prevalence of HIV infection, L. monocytogenes caused disproportionate illness among pregnant girls and women and HIV-infected persons. Whole-genome sequencing facilitated the detection of the outbreak and guided the trace-back investigations that led to the identification of the source.

Authors
Juno Thomas, Nevashan Govender, Kerrigan M McCarthy, Linda K Erasmus, Timothy J Doyle, Mushal Allam, Arshad Ismail, Ntsieni Ramalwa, Phuti Sekwadi, Genevie Ntshoe, Andronica Shonhiwa, Vivien Essel, Nomsa Tau, Shannon Smouse, Hlengiwe M Ngomane, Bolele Disenyeng, Nicola A Page, Nelesh P Govender, Adriano G Duse, Rob Stewart, Teena Thomas, Deon Mahoney, Mathieu Tourdjman, Olivier Disson, Pierre Thouvenot, Mylène M. Maury, Alexandre Leclercq, Marc Lecuit, Anthony M Smith, Lucille H Blumberg

Full Business Day report

New England Journal of Medicine abstract

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