GERMANTOWN, Wis. (AP) — The Wisconsin company that distributed the nacho cheese dip linked to a fatal botulism outbreak in California says the organization is working with federal, state and local health officials to determine what caused the contamination.

Tests confirmed the botulism toxin was present in nacho-cheese dip sold at a gas station in the Sacramento suburb of Walnut Grove that killed one man and left at least nine other hospitalized. The cheese dip was distributed by Gehl Foods.

The Germantown company says it retested samples from the lot of cheese linked to the outbreak and that it’s clear of contamination. It also sent samples to an independent lab which confirmed the findings.

On Monday, Matt Conens, a spokesman for the California Department of Public Health, declined to release further information on the death, the condition of the other victims, or the status and extent of the investigation into the weeks-old outbreak.

The agency said last week the container and cheese dip were removed May 5, and that authorities believe the contamination posed no further risk to the public.

Spokesmen for the state health agency said they did not immediately whether authorities think the contamination occurred at the station or were checking other gas stations and the maker of the cheese sauce.

Botulism, a comparatively rare kind of food poisoning, can lead to paralysis, breathing difficulty and sometimes death. Survivors often are forced to spend weeks or months on ventilators to help them breathe.

A major outbreak of food-borne botulism stemmed from a church potluck in Ohio in 2015, when at least 29 people fell ill. Authorities blamed potato salad made from potatoes that had been canned improperly at home.