Reference strain link in Chilean Salmonella outbreak

A Salmonella outbreak that sickened more than 130 people in Chile may have been caused after food was contaminated with a strain used to monitor testing performance.

The Salmonella Abony outbreak occurred from January to April 2024. Genomic evidence indicated that the outbreak strain was a clone of a reference strain, which is routinely used in microbiological quality control tests.

According to information published in the journal Emerging Infectious Diseases, two healthcare centers in Santiago diagnosed 134 salmonellosis cases from January to March: 29 at UC-Christus and 105 at Clínica Alemana. All isolates were submitted to Instituto de Salud Pública de Chile for serotyping.

Salmonella Abony was found in 56 of 97 cases with culture. Of these, 33 patients were male and 23 were female. Forty were under 18 years old, 17 required hospitalization, and 10 had bacteremia.

18 of 56 outbreak isolates were subjected to whole genome sequencing. The samples were from blood, urine, and feces.

Outbreak of rare Salmonella type

According to data from the Government of Chile, 287 Salmonella Abony isolates were collected between January and April from 12 of 16 administrative regions. Some isolates may have been obtained from the same patient. Infected people ranged in age from under 1 to 82 years old. More than 200 isolates came from Región Metropolitana, and 165 were obtained in February 2024.

However, scientists did not have additional epidemiological information, such as the food consumed by sick people, so they could not investigate the outbreak’s source.

Previous studies from Brazil and Nigeria reported on Salmonella Abony infections, and cases from Brazil were linked to the consumption of food containing chicken meat.

The reference strain, WDCM 00029, is widely used as a control strain for testing culture media performance. Many suppliers sell it as certified lyophilized or ready-to-use reference material for quality control of food, water, and environmental testing.

Researchers said the evidence suggests the Salmonella Abony outbreak was caused by contamination of an unknown vehicle with the common reference strain. The findings raise concerns about the safety of bacterial quality control strains. Clinicians and health authorities should request strain characterization when rare or unreported serovars cause human infections.

Data from the Chilean Agency for Food Safety and Quality (ACHIPIA) shows 728 outbreaks in 2022, with 3,764 cases, 131 hospitalizations, and one death.

The three main agents associated with outbreak cases from 2016 to 2021 were Salmonella, scombroid (histamine) fish poisoning, and Norovirus. Salmonella infections were mainly linked to ready-to-eat food, meat products, or egg products.

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