CDC Re-Opens Salmonella Outbreak Investigation

New human cases of Salmonellosis caused by Multi-drug Resistant (MDR) Salmonella Heidelberg spark re-opening of outbreak investigation


A multi-state outbreak investigation that began in July 2016 after a 16-year-old boy became ill after buying calves for a 4-H project has been re-opened by the Centers for Disease Control and Prevention (CDC). As of August 2, 2017 there have been 46 confirmed human cases of MDR Salmonella enterica subspecies enterica serotype Heidelberg reported to the CDC and other local health officials, with ten of these cases reported since April 2017. The outbreak now spans across 14 states and has hospitalized 14 (30%) people. Two-thirds of people reported having contact with dairy bull calves or other cattle just prior to onset of symptoms. More than half of the illness in Wisconsin occurred in children under 10 years of age.

Whole genome sequencing confirmed that 33 human, 65 cattle and 11 environmental samples have multiple antimicrobial resistance genes leading to no available antimicrobial for treatment of bovine illness and few treatment options for human illness.  Whole genome sequencing of human, bovine and environmental isolates also confirmed that these strains are highly related.  There are two main variants of this Salmonella ser. Heidelberg in the cattle population and one them is highly pathogenic.  Most cases identified are from the highly pathogenic strain and in Wisconsin only the highly pathogenic strain has been identified.

Although no new human cases have been identified in Wisconsin since December 2016, the WVDL has isolated more than twice the amount of MDR Salmonella ser. Heidelberg than this time last year indicating the outbreak has not slowed in the cattle population. The WVDL continues to work closely with other state and federal officials to monitor and prevent the transmission of MDR Salmonella ser. Heidelberg from cattle to humans.

More information on this on-going investigation and to stay up-to-date on recent happenings, see the links below for several federal, state and local websites.


Center for Disease Control and Prevention (CDC)

Wisconsin Department of Health Services

Wisconsin Department of Agriculture, Trade and Consumer Protection

Wisconsin Veterinary Diagnostic Laboratory