Italian Salmonella outbreak traced to raw milk cheese

Italian Salmonella outbreak traced to raw milk cheese

by Sue Jones
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Raw sheep milk cheese was behind a Salmonella outbreak in Italy that affected more than 80 people in 2020, according to a study.

In April and May 2020, an outbreak of Salmonella Enteritidis occurred in the Marche region of Central Italy, involving 85 people.

An epidemiological investigation identified the unpasteurized, raw sheep milk pecorino primo sale cheese produced by two local dairies as the most probable source, since all cases said they had consumed this product.

The first dairy was part of a livestock production facility also including a sheep farm and supplying milk to the second dairy. The former sold its cheese directly to the consumer, while the latter distributed its products to the local market chain.

Poor farm conditions and milk handling
Analysis of samples detected Salmonella Enteritidis in animal feces, environmental samples, raw milk bulk tanks and milk taken from animals. However, the original source of Salmonella remained unknown, according to the study published in the journal Microorganisms.

In Italy, Salmonella Enteritidis is constantly among the main five serovars isolated from humans, and was the seventh most common type among all animal and food isolates in 2018, with an increase from the previous year.

There is limited information on the occurrence of Salmonella in sheep and the role of raw sheep milk as a source of salmonellosis, said researchers.

The study provided evidence of intestinal and udder infection due to Salmonella Enteritidis in sheep with shedding in milk.

Samples were collected during visits in April and May. After sanitization of the farm, more tests were taken in June and sampling sessions continued until November.

An inspection at the farm revealed general hygienic standards were unsatisfactory and milk was held for more than an hour in milking buckets at a temperature of 37 degrees C (98.6 degrees F) before being transferred to the cooling tank.

Positive samples
All 10 samples of pecorino primo sale cheese collected from the cases’ homes and 18 of the 25 samples from the first dairy were positive for Salmonella Enteritidis.

One of 48 fecal pools and the bulk milk, sampled in April, were positive. In May, three of seven fecal samples taken from the floor and two of four boot swabs were positive. Until July, all samples of bulk milk collected before and after the environmental sanitization were positive.

The Salmonella Enteritidis type behind the outbreak had not been observed before in the Italian human database, Enter-Net, or the food and veterinary one, Enter-Vet. An analysis of the European Centre for Disease Prevention and Control (ECDC) database indicates it was only detected in one other case in 2018.

“Satisfactory hygienic standards and the adoption of prevention measures and good processing techniques in farms and dairies are fundamental for preventing sheep milk contamination with Salmonella, especially if raw milk is destined for human consumption or is used in further production that does not include a pasteurization step,” said researchers.

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