A Surveillance Study of Fresh Cantaloupe from Indiana Farms Following 2012 Salmonella Outbreak

Introduction: As a result of the 2012 Salmonella outbreak associated with Indiana grown cantaloupe, the Indiana State Department of Health (ISDH) started a new food safety surveillance initiative to collect fresh produce samples from Indiana wholesale produce farms and analyze them for the presence of bacteriological contamination.

Purpose: The goal is to prevent the distribution of these contaminated products to the consumer and avert foodborne illness outbreak.

Methods: Cantaloupe and watermelon samples collected for this surveillance initiative were enriched by totally submerging the whole sample into selective media and were incubated overnight. For Salmonella screening, aliquots were transferred and tested using BAX Q7 Salmonella kits. For Listeria spp., aliquots were transferred and tested using VIDAS LIS kits. All presumptive positive results from the screening steps were followed by culture confirmation assay recommended by the U.S FDA BAM method. Additionally, all confirmed positive samples were also confirmed with VITEK 2Comp and MADLI-Biotyper. Finally, all confirmed Salmonella and Listeria monocytogenes were further analyzed by PFGE and posted to PulseNet. 

Results: Samples were collected from 5 farms in the northern part of the State and 11 farms in southern part of the State. Cantaloupes were collected during July, August, September and October 2013. A total of 76 cantaloupes and 7 environmental swabs were collected and tested for Salmonella spp. Another 68 cantaloupes and 54 environmental swabs were also collected and tested for Listeria spp.

Salmonella spp. was detected in 4 cantaloupes (5.3% of total samples). Only one Salmonella isolate matched the previous year outbreak. Over 16% of the samples tested for Listeria spp. were confirmed positive (11 samples). Among these, 3 (27%) were Listeria monocytogenes from cantaloupe samples. Overall, bacterial contaminants, Salmonella or Listeria, were detected from 10% of all the samples analyzed.

Significance: ISDH Food Protection Division was able to communicate with the farmers where Listeria monocytogenes was isolated and advise them to voluntarily remove the remainder of these products from commerce.  In addition, this data was used by the ISDH Food Safety Farm Consultants to provide education and outreach, technical assistance and environmental assessments to the Indiana produce farmers.