The US Food and Drug Administration has linked the outbreak of salmonella stpaul that has swept the US to a sample of serrano pepper and irrigation water collected from a farm in Mexico.

The FDA has therefore advised consumers to avoid eating raw Mexican serrano peppers. The food safety watchdog still maintains previous guidance to steer clear of raw Mexican jalapeños.

However, the FDA did emphasise that US-grown peppers were considered safe. Commercially canned, pickled and cooked jalapeño and serrano peppers from any location also are not connected with the outbreak, the food safety watchdog said.

Previously, FDA inspectors tested a sample of a jalapeño pepper that came back positive for the stpaul virus. The pepper had been collected from Agricola Zaragosa's produce-distribution centre in McAllen, Texas.

The agency said that its efforts to identify where in the supply chain the jalapeño became infected are ongoing.