Scientists uncover manure tank’s role in Salmonella outbreak

A manure storage tank in a buffalo farming region in Italy likely played a role in a major European Salmonella outbreak, according to researchers.

In 2024, a significant Salmonella Umbilo outbreak was reported across the European Union, traced to contaminated produce from Salerno in Italy. Subsequent onsite inspections in the production area revealed a mismanaged manure storage tank.

Within a 1-km radius — including both the tank and contaminated greenhouses — three buffalo farms were identified. Inspections revealed buffalo calves with enteric symptoms. Fecal samples from these animals led to the isolation of Salmonella Umbilo genomically linked to the multi-country outbreak, as well as other serotypes.

Manure tank problem
The serious public health alert between July and December 2024 led to cases in Germany, Austria, Denmark, Italy, Switzerland and the United Kingdom. More than 200 infections and one fatality were reported. Germany was the most affected with 118 cases.

The outbreak was epidemiologically linked to the consumption of rocket salad and organic baby spinach from Italy. Investigations by Italian authorities identified the production area of implicated vegetables as the Province of Salerno, in the Campania Region, an area known for intensive buffalo farming. No national programs are in place for the control of salmonellosis in ruminants. 

A study published in the International Journal of Environmental Research and Public Health revealed that field investigations were conducted between November 2024 and January 2025 by local and regional authorities to assess potential sources of environmental contamination in the area surrounding the greenhouses linked to the outbreak.

Inspections of this area led to the discovery of an unauthorized and mismanaged manure storage tank, apparently intended for a nearby livestock farm.

The uncovered manure storage tank of unknown ownership posed a significant risk of overflowing into adjacent irrigation canals when at full capacity. Because of improper management and during rainy periods, animal waste from surrounding farms may have entered the drainage systems, potentially introducing microbial pathogens into the agricultural environment. Scientists said delayed collection of two samples from the manure tank might explain the negative microbiological results.

Positives from buffaloes
At the end of 2024, during the epidemiological investigation by veterinarians in the three buffalo farms within the 1-km radius surrounding the manure storage tank, buffalo calves with enteric symptoms were identified. Analyses of fecal samples confirmed salmonellosis outbreaks involving calves born in November and December.

Four buffalo calves tested positive for Salmonella Senftenberg. In the second establishment, six calves tested positive for Salmonella Umbilo. In the third farm, six calves were positive for Salmonella Livingstone. These findings prompted targeted measures to address the outbreaks and prevent the spread among livestock, horticultural products and humans.

Scientists also said current datasets in open access platforms, covering human cases, associated clinical complications, and genomic analyses of isolates from animals, food, feed, and environmental samples, are insufficient.

“This lack of comprehensive open access data severely limits the ability to reconstruct events leading to public health emergencies, to understand epidemiological links across sectors, and to align and compare findings obtained by different laboratories and institutions,” they added.

“Ultimately, broader access to epidemiological and microbiological data could greatly improve the speed and effectiveness of outbreak investigations, enabling the rapid identification of the origin of epidemics and immediate interruption of transmission chains, thereby protecting human, animal, and environmental health.”

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