Mar 4, 2013 (CIDRAP News) – Salmonella contamination in an Indiana grower's melons linked to a 2012 outbreak likely occurred in the growing fields and was likely spread during various handling stages, according to an environmental assessment by the US Food and Drug Administration (FDA).
The findings, posted Mar 1 on the FDA's Web site, describe an extensive investigation of cantaloupe and watermelon growing operations at Chamberlain Farms in Owensville, Ind., that took place in September after an initial inspection found one of the outbreak strains in the packing area, two outbreak strains from cantaloupes collected from the field, and one outbreak strain from a watermelon growing area.
The outbreak sickened at least 261 people, 3 of them fatally, in 24 states, according to the CDC's final outbreak report on Oct 5. The illnesses were linked to eating the company's cantaloupe and involved two outbreak strains, Salmonella Typhimurium and Salmonella Newport.
A multidisciplinary team of experts from the FDA and the Indiana State Department of Health conducted the environmental assessment. Their task was to explore all potential routes for contamination in the fields and in the packinghouse areas.
They collected a range of environmental samples from the farm's four growing fields, which were all located within about 3 miles of the packinghouse. They also analyzed six different water wells that served the growing area and packinghouse.
Signs of deer, coyotes, and toads were found in the fields, including coyote scat. One of the four fields was reportedly not irrigated during the 2012 growing season.
After analyzing their findings, investigators write that initial contamination probably occurred in the field and was spread during packinghouse operations and amplified during storage and transportation. Soil samples, environmental water samples, and cantaloupe remaining in the field all tested positive for several Salmonella serovars, including some that were indistinguishable from the outbreak strains.
Biological soil amendments could have been the source of the pathogen, but the farm reported that it doesn't use them for growing cantaloupe or watermelon. The FDA said it's not clear if previous or adjacent land use may have played a role, and it noted that a significant turkey operation is located in the region where the farm is located.
Though the growing fields were the most likely source, the organisms could have established a niche in the packing and storage areas, the investigators wrote.
Agricultural water sources tested negative for Salmonella and probably didn't introduce the pathogen, but the inspectors didn't eliminate it as a potential contributor to its spread, because the quality of the water may not have been adequate. Some of the wells tested positive for generic Escherichia coli and total coliform, and some were poorly constructed or were in disrepair. "Use of agricultural water in these operations may have acted as a vehicle to spread contamination, once introduced," they added.
The group noted that the packinghouse equipment wasn't easily cleaned or sanitized, which could have contributed to the problem, as well as moisture on the fruit after packing and inadequate cooling.
The FDA has several recommendations for growers, such as making sure all equipment is cleanable and that high-quality water is used in processing steps. The report also emphasized the importance of reducing surface moisture and cooling and storing melons as soon as possible after harvest.
Release of the FDA's Chamberlain Farms environmental assessment comes just days after the agency sent a letter to the cantaloupe industry urging it to use best growing and packing practices in the wake of recent Listeria and Salmonella outbreaks linked to eating cantaloupe. Given recent outbreaks, the FDA announced that during the 2013 growing season it will inspect and sample a subset of growers to assess any potentially unsafe conditions.
Oct 3, 2012, CIDRAP News scan "FDA lists problems at cantaloupe farm tied to Salmonella outbreak"
Oct 5, 2012, CDC final outbreak update
Feb 26 CIDRAP News scan "FDA beefs up cantaloupe packer inspections"