According to researchers, mandatory reporting of Listeria infections in Costa Rica would help improve knowledge of the pathogen in the country.

Listeriosis is not a notifiable disease in the country, so its prevalence is unknown, and the diversity of Listeria monocytogenes circulating is unclear.

Previous studies found Listeria monocytogenes in various foods in Costa Rica, with contamination levels between 5 and 20 percent in processed meat products and fresh cheeses.

Researchers used whole genome sequencing (WGS) to characterize 92 isolates recovered from 2009 to 2019 from 16 clinical, 67 food, and nine production environment samples.

Isolates were from urban areas, including the capital city, San José, and from rural zones wher cheese production is prevalent, including Turrialba, which accounts for 70 percent of fresh cheese made in the country.

The risk from contaminated dairy
The team identified 48 core-genome multilocus sequence typing (MLST) types, of which 44 were not previously reported. Eleven included multiple isolates found in the study published in the journal Emerging Infectious Diseases.

Most human cases were associated with dairy products. However, traceback work to confirm the source of infection was impossible because most production is by local farmers, often without traceability or attribution to the production site.

Results showed the detection of identical strains along the same production line, from raw materials to the final product, suggesting inadequate sanitation contributes to contamination.

Most isolates had genes indicating tolerance to disinfectants, pH or stress. This can make Listeria elimination from production sites more difficult, said scientists.

“This study provides insight into the diversity of Listeria monocytogenes strains circulating in Central America and can aid national reference institutions in promoting regulatory changes to guarantee mandatory listeriosis reporting. We also recommend regular sampling of risk products and training of artisanal processors,” said researchers.

“Strengthened WGS surveillance in Costa Rica could assist in controlling Listeria monocytogenes and provide food producers with information on strain diversity and effective means of eradication. WGS surveillance also would enable authorities to detect outbreaks and trace sources of contamination.”

Listeria in Ecuador
Another study has looked at Listeria monocytogenes isolated from fresh cheeses and clinical samples in Ecuador.

Sixty-five isolates were sequenced, 14 from cheese samples, 20 from clinical listeriosis cases, and 31 from artisanal cheese samples in eight provinces. Findings were published in the journal Frontiers in Microbiology.

Listeriosis is a notifiable disease in North America and many European countries, but not Ecuador. The country also doesn’t have a national surveillance program for the pathogen.

Scientists say that a particular sequence type in food and clinical samples, with high genomic similarity, suggests a foodborne infection risk linked to fresh cheeses in Ecuador.