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Outbreak of Listeriosis in South Africa Associated with Processed Meat
Juno Thomas1, Nevashan Govender1, Kerrigan M McCarthy1
1From the Centre for Enteric Diseases (J.T., N.R., P.S., N.T., S.S., H.M.N., B.D., N.A.P., A.M.S.), the Division of Public Health Surveillance and Response (N.G., K.M.M., L.K.E., G.N., A.S., V.E., L.H.B.), the Sequencing Core Facility (M.A., A.I.), and the Centre for Healthcare-Associated Infections and Antimicrobial Resistance (N.P.G.), National Institute for Communicable Diseases, National Health Laboratory Service, the University of the Witwatersrand (K.M.M., N.P.G., A.G.D., T.T., A.M.S.), and the School of Pathology, National Health Laboratory Service (A.G.D., R.S., T.T.), Johannesburg, the Division of Global Health Protection, Center for Global Health, Centers for Disease Control and Prevention, Pretoria (T.J.D.), the University of Pretoria, Tshwane (N.R., G.N., N.A.P.), and the University of Stellenbosch, Stellenbosch (L.H.B.) - all in South Africa; Deon Mahoney Consulting, Melbourne, VIC, Australia (D.M.); and Santé Publique France, the French Public Health Agency, Saint-Maurice (M.T.), and Institut Pasteur, Biology of Infection Unit, INSERM Unité 1117 and National Reference Center-WHO Collaborating Center for Listeria (O.D., P.T., M.M.M., A.L., M.L.), and Université de Paris, Division of Infectious Diseases and Tropical Medicine, Necker-Enfants Malades University Hospital, Assistance Publique-Hôpitaux de Paris, Institut Imagine (M.L.), Paris - all in France.
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.
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