Listeria has been found in samples of cantaloupes and packaging equipment at Jensen Farms, the company linked to the deadly Listeria outbreak in the US.
So far 35 people across 10 states have been infected and four have died – an increase on the 22 confirmed cases last week.
Another two deaths in New Mexico are being unofficially attributed to the infection and are waiting to be confirmed by the Food and Drug Administration (FDA).
The agency has confirmed that Listeria monocytogenes bacteria has been found in Jensen Farms cantaloupes from a Denver store, and on samples taken from machinery at the company's Colorado packaging plant.
An investigation by state, local and federal public health agencies had linked eating whole cantaloupe from Jensen Farms in Colorado to the outbreak of Listeria, but it has taken until now to confirm that Listeria monocytogenes bacteria was present in samples of the farm’s cantaloupes.
The FDA were also able to confirm that the Listeria monocytogenes bacteria found in samples of Jensen Farms cantaloupes and equipment, matches one of the three strains associated with the multi-state outbreak.
Inter-agency investigations led authorities to suspect Listeria had originated from Jensen Farms Rocky Ford cantaloupes.
Since then, Jensen Farms have been helping federal and state authorities in the US determine how the cantaloupes became contaminated, as well as voluntarily recalling all cantaloupes shipped between the 29 July and 10 September.
The FDA has also been working with microbiologists, environmental health specialists and veterinarians in Colorado to establish the most likely cause of contamination at Jensen Farm.
They will use these findings in future to help enforce policy change regarding Listeria and produce best practice for food safety.
The Centre for Disease Control and Prevention (CDC) have urged consumers to throw away any Rocky Ford cantaloupes, potentially infected with the Listeria monocytogenes bacteria, which have so far been distributed to at least 17 states.