An investigation into a Salmonella outbreak in two regions of Portugal traced to cheese has revealed problems at the production site.
A case–case study suggested fresh cheese as the likely vehicle of the Salmonella Typhimurium outbreak. The case–case approach compares outbreak and historical cases.
In Portugal, Salmonella Typhimurium is the second most common serotype, after Salmonella Enteritidis, with yearly case numbers ranging between 262 and 535 since 2015, far below the EU average.
In April 2024, the Directorate-General of Health (DGS) was informed about an unusual increase in a Salmonella Typhimurium strain by the National Reference Laboratory (NRL) for Gastrointestinal Infections at Instituto Nacional de Saúde Doutor Ricardo Jorge (INSA), representing more than a fivefold rise compared with the same period in the previous year. The increase started around late March.
Clinicians at the hospital in Évora, in Alentejo, noticed an increase in salmonellosis among patients admitted with gastrointestinal complaints, and the local public health units of Alentejo and Arrábida observed more cases reported through the National Epidemiological Surveillance System (SINAVE).
Epidemiological inquiries found that many patients had consumed cheese from a local producer. The outbreak investigation team included local and regional public health units, NRL/INSA, the Directorate-General of Food and Veterinary (DGAV), and DGS.
Among the 65 isolates identified as part of the cluster by whole genome sequencing, 58 were included in the epidemiological analysis. The outbreak began on March 11, peaked on April 1, and ended on June 18, 2024. In total, 33 men and 25 women fell sick. The most affected age group was up to 17 years old followed by those older than 65, according to a study published in the journal Epidemiology and Infection.
Problems at cheese producer
Among the first 17 notified Salmonella cases, eight had eaten a specific brand of fresh cheese from the same producer during the incubation period. Of these, seven reported purchasing it at the same market.
During a visit to the producer, actions included a review and strengthening of hygiene and sanitation procedures, verification of cleaning and disinfection protocols, assessment of staff food handling practices, and reinforcement of traceability and record-keeping requirements.
Three cheese specimens and two surface swabs from the site as well as four cheese and three surface swabs from the market were collected. All were negative for Salmonella.
Only some of the previously required measures were implemented, leading the health authority and DGAV to impose additional controls. Because of delays in implementation, production was suspended on July 19 until all requirements were met.
