An International Outbreak of Tetracycline-Resistant Salmonella I 4,[5],12:I:- Infections Associated With Frozen Feeder Rodents Used as Reptile Feed —2008-2012

BACKGROUND:  An estimated 127,000 cases of human salmonellosis are attributed to animal exposure each year in the United States. An international outbreak of tetracycline-resistant Salmonella I 4,[5],12:i:- occurred over several years with cases in the United States, the United Kingdom, and Canada.  We investigated a 2010 multistate outbreak that occurred as part of this international outbreak.

METHODS:  A case was defined as illness in a person infected with the outbreak strain of Salmonella I 4,[5],12:i:- between 1/1/2010 and 7/30/2010.  Ill persons were interviewed regarding reptile and rodent exposure, a case-control study was conducted, and ill persons provided purchase records for product tracing. Isolates from ill persons and environmental investigations were tested for antimicrobial resistance.

RESULTS:  We identified 34 cases in 17 states; 47% were female with the median age 12 years (range <1 to 57 years). Illness was significantly associated with exposure to reptiles (73% versus 14%, matched Odds Ratio 15.8, 95% confidence interval [CI]: 2.2 – 690.3) and feeder rodents used as reptile food (60% versus 3%, median unbiased estimate 21.4, CI: 3.3 – ∞).  Only 13% of cases reported awareness of the association between rodents and Salmonella.  Product tracing from United States cases was difficult, but Distributor A was identified as a common source of contaminated frozen feeder rodents (FFR) via the United Kingdom investigation. The outbreak strain was isolated from environmental samples and FFR obtained during an inspection of Distributor A, leading to a recall of over 6 million FFR sold between 05/2009 and 07/2010. All isolates tested - those from 3 ill persons, plus environmental and FFR samples from Distributor A - demonstrated tetracycline-resistance. Between 08/2010 and 02/2012 we continued to interview persons from whom the outbreak strain was isolated due to the long shelf life of the product; 89 additional  U.S. cases were identified. Of those interviewed, 74% reported exposure to reptiles and 56% reported exposure to rodents.  The United Kingdom identified > 400 cases and Canada identified >20 cases related to this outbreak.

CONCLUSIONS:  Over 500 persons were infected with the outbreak strain as a result of contaminated FFR from Distributor A.  United States cases occurring during 2011-2012 could not be definitively linked to Distributor A, possibly due to point of sale re-packaging and poor labeling. Packaging and labeling changes are needed within the FFR industry. Pet stores and veterinarians should encourage diligent hand hygiene after handling or feeding reptiles.