The agency and the Centers for Disease Control and Prevention launched their investigations last summer after the start of an outbreak of the illness that ultimately sickened 261 people in 24 states and killed three people in Kentucky.
The FDA's letter states that among the problems found in the farm's fruit-packing building was bird excrement on the building's rafters directly above conveyor belts, a fruit-grading table and brushes used to clean melons. Inspectors also found salmonella on one conveyor belt and carpet used on a fruit-grading table to prevent fruit from being bruised.
The letter also said samples collected in September in fields at the farm more than a mile apart contained multiple salmonella samples "indistinguishable" from the salmonella found in patients stricken with the food-borne illness and on cantaloupes the farm had packaged.
"FDA does not expect melons to be grown in a Salmonella free environment; however these findings suggest a source of contamination that is widespread and not consistent with background contamination," the letter states.
FDA spokeswoman Pat El-Hinnawy said Thursday the agency sends warning letters when its investigators find problems "that cannot be corrected easily."
She said the FDA's investigation of the salmonella outbreak is still under way and she could not comment on whether Chamberlain Farms has responded to the agency's letter seeking information on the steps the farm has taken to address the packing building's unsanitary conditions.
"Our concern is the safety of the food that leaves that farm, which they are responsible for," El-Hinnawy said.
The FDA announced in August that genetic testing on salmonella collected at the farm matched the "DNA fingerprint" of the salmonella strain responsible for this summer's outbreak, making it a source for at least some of the bacteria.
Gary Zhao, an attorney for Chamberlain Farms, said the farm was sending its response to the FDA's letter Thursday.
He said he could not comment on how the outbreak and subsequent investigation had impacted the farm financially, but Zhao said in a Thursday statement that testing by a microbiologist hired by the farm suggests the bacteria that caused the outbreak did not come from the farm's fields.
He said "overwhelming evidence" points to land adjacent to the Owensville farm's melon fields — and not the farm's packing facilities, equipment or operations — as the likely source of the bacterial contamination investigators found on the farm's cantaloupes.
Nonetheless, Zhao said the farm has decided not to grow cantaloupes this year and has already dismantled and disposed of its cantaloupe packing equipment. He said the farm has also tested well water used to irrigate its fields and upgraded the wells "to reduce the chance of any bacterium that may be present on the land contaminating well water."
Zhao added that the farm "will continue to work with the FDA cooperatively to further delve into the root cause and source of contamination so that lessons can be learned for the benefit of others who are later engaged in cantaloupe production."