Human cases of Salmonella serotype Oranienburg infection are relatively rare, and comprise 2.2% and 1.5% of all Salmonella serotypes in Missouri and USA, respectively. In April 2015, the Missouri Department of Health and Senior Services (MDHSS) was notified of four S. Oranienburg cases. A joint outbreak investigation with local public health agencies was initiated by the MDHSS.
METHODS:
Outbreak investigation included an epidemiological, laboratory, and environmental investigations. Case interviews were conducted using Oregon’s “Shotgun” hypothesis-generating questionnaire and an outbreak-specific questionnaire developed according to the dynamic cluster investigation model. S. Oranienburg isolates were typed by the Missouri State Public Health Laboratory (MSPHL) using pulsed-field gel electrophoresis (PFGE) with one and two enzymes, and select isolates were genotyped by Whole Genome Sequencing (WGS) at the CDC. Environmental assessment included inspection of the implicated facilities, food sampling by the MDHSS and the FDA, and environmental sampling.
RESULTS:
Outbreak strain was defined as S. Oranienburg with the PFGE pattern JJXX01.0027 or JJXX01.0027/JJXA26.0020. During April 22-November 26, 46 case-patients infected with this strain were identified. Median age of cases was 40.3 years (range, <1 to 87 years). The incubation period was prolonged, ranging from 3 to 14 days. Twenty-five (54%) cases reported eating at Restaurant Chain A within 2 weeks before becoming ill. Seventeen (68%) of those cases consumed eggs (binomial probability of egg exposure p= 0.002). Traceback revealed that all implicated restaurants used the same local egg producer. Six of 31 environmental samples from that egg producer’s facility tested positive at the MSPHL for the outbreak strain of S. Oranienburg. Laboratory testing of the farm eggs contents by the FDA was negative for Salmonella, but the outbreak strain was recovered from 7/16 environmental specimens. All genotyped Missouri isolates were identical by WGS, but differed from four S. Oranienburg isolates with similar PFGE pattern reported to the PulseNet from other states during the outbreak.
CONCLUSIONS:
This outbreak underscores importance of the One Health concept. Most likely, manure from the Salmonella infected chicken flock contaminated environment in the facility with subsequent contamination of the eggshells, and eventually resulted in human outbreak of salmonellosis after those eggs were consumed. Collaboration of multiple local, state and federal agencies was needed to resolve this outbreak.