Increased Awareness for Multi-drug Resistant Salmonella Heidelberg Infections

Notice of Increased Awareness for Multi-drug Resistant Salmonella enterica subspecies enterica serotype Heidelberg

High zoonotic potential for farm workers, especially children

Recently, the Wisconsin Veterinary Diagnostic Laboratory (WVDL), the Wisconsin Division of Public Health (DPH), the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP), the Wisconsin State Laboratory of Hygiene (WSLH) and the Centers for Disease Control and Prevention (CDC) have been tracking a multi-drug resistant (MDR) strain of Salmonella enterica subspecies enterica serotype Heidelberg (Group B).  The reason for this close collaboration is the strong connection between human infections and recent bull calf purchases.  The purpose of this communication is to educate the veterinary community of the risk these MDR Salmonella Heidelberg pose to both cattle and people, provide testing options for diagnosis, and disinfection recommendations.

Currently, there are twelve confirmed human infections from seven Wisconsin counties in 2016. The median age for Wisconsin residents with Salmonella Heidelberg infections is 7 years old, and four individuals were hospitalized.  Upon interview, greater than 90% of the infected individuals reported purchasing Holstein bull calves from livestock dealers or sales barns. Many of these calves died shortly after becoming ill.  During 2015 and 2016, the WVDL has isolated several MDR Salmonella Heidelberg isolates from calves located in mostly Wisconsin, but isolation has also occurred from calves located outside of Wisconsin during 2015 and 2016.  Pulsed-field gel electrophoresis (PFGE) and whole genome sequencing of 2016 isolates indicates that the human and bovine Salmonella Heidelberg isolates are very closely related, and may share a common source.  This strain of Salmonella Heidelberg is highly pathogenic and multi-drug resistant; only one antimicrobial drug is an effective treatment option for human cases and no effective options exist for cattle.  Individuals working with sick pre-weaned calves, particularly bull calves that have been recently purchased, are recommended to adhere to strict biosafety protocols and wash hands, change clothing, and clean affected areas and items frequently.  Children and immunocompromised individuals should limit their access to calves with diarrhea.  Additionally, any human diarrheal illnesses should be seen by a physician and reported to DPH if salmonellosis is confirmed.

Veterinarians suspecting salmonellosis, particularly infection caused by Salmonella Heidelberg, should submit fecal samples for Salmonella culture and/or PCR to the WVDL.  Results for confirmation of Salmonella are within 24-72 hours with serotyping taking an additional 24-72 hours.  Fecal samples should be collected in a leak-proof vial rather than glove, Whirl pack, or bag as these are more likely to leak.  Culture-positive Salmonella isolates will be serotyped and Salmonella Heidelberg isolates will be subject to antimicrobial susceptibility testing to confirm MDR status. WVDL staff veterinarians will contact submitting veterinarians upon isolation of this MDR Salmonella Heidelberg to discuss herd health, provide cleaning and disinfection recommendations and supply the veterinarians with an interview questionnaire to be filled out.

Cleaning and disinfection is absolutely necessary after confirmation of Salmonella as the cause of calf diarrhea or adult enteric disease.  This is particularly important for this particular MDR Salmonella strain, given the human and bovine health implications and lack of antimicrobials available.  Reinfection on the affected premise is highly likely and has been detected with this outbreak; therefore, it is highly recommended to perform environmental testing for Salmonella.  The WVDL has kits specific to this type of testing and cleaning and disinfection protocols that producers can use.

The WVDL, DATCP and DPH would like to increase surveillance for MDR Salmonella Heidelberg and encourages veterinarians to submit diagnostic samples when possible.  Veterinarians, please encourage producers to submit samples from suspect animals, particularly pre-weaned dairy calves that were recently purchased and die suddenly and unexpectedly.  Other state veterinary diagnostic laboratories have been notified of this outbreak and are prepared to culture diagnostic samples for Salmonella.  Salmonella Group B or Heidelberg isolates will be submitted to NVSL for PFGE and whole genome sequencing.  Cooperation between Wisconsin veterinarians, producers, and the human and animal health officials should reduce the incidence rates of salmonellosis in both humans and animals.

For more information please contact the following authorities:

Wisconsin Veterinary Diagnostic Laboratory at 608-262-5432 and or The WVDL will respond to requests within 24-48 hours during the work week.

Wisconsin Division of Public Health at 608-267-7143 and

Department of Agriculture, Trade, and Consumer Protection at 608-224-5012