Authors: Amelia Keaton, R. Hassan, S. Luna, I. Lee, R. Magalhaes, M. Bidlack, L. Smith, R. Maves, D. Freer, K. Flinn, G. Monk, P. Graf, K. Trinh, J. Crandall, D. Noveroske, G. Fortenberry, L. Ramos, R. Recio, C. Peak, E. McDonald, T. Waltz, K. Patel, D. Wagner, J. Espiritu, L. Christensen, L. Gieraltowski

Background: Shiga toxin-producing Escherichia coli (STEC) infections are a substantial cause of foodborne illness and a cause of hemolytic-uremic syndrome (HUS). In November 2017, CDC assisted the US Navy in a response to an outbreak of STEC illnesses in recruits at a Marine Corps Recruit Depot in San Diego (MCRD). We investigated to determine the source of this outbreak and identify prevention and mitigation measures.

Methods: In October 2017, medical providers identified a high number of gastrointestinal (GI) illnesses at MCRD. Recruits with diarrhea submitted stool specimens for culture and/or culture-independent diagnostic testing (CIDT) for GI pathogens. We performed pulsed-field gel electrophoresis (PFGE) on culture isolates. Case-patients were then defined as follows: confirmed (PFGE-confirmed STEC infection matching outbreak strains), probable (diagnosis of HUS and/or CIDT evidence of STEC), and suspected (bloody diarrhea). We conducted environmental evaluations of facilities, training areas, and barracks. A case-control study was performed using PFGE-confirmed case-patients and platoon-matched controls. We performed product traceback for foods identified as exposure risks by interview or case-control study.

Results: We identified 62 confirmed, 62 probable, and 120 suspected case-patients. Thirty case-patients required hospitalization and 15 had HUS. Case-patient ages ranged from 17-28 years (median: 18 years). Poor hygiene practices among recruits and inconsistent cooking temperatures within dining facilities were noted. Forty-three case-patients and 135 controls were interviewed about food, hygiene, and environmental exposures. Consumption of undercooked beef was found to be significantly associated with illness, (mOR 2.40, CI 1.04-5.72, p=0.04). We identified a single ground beef supplier for MCRD, but MCRD records did not document which specific lots of ground beef were used.

Conclusions: Case-control analysis and environmental observations suggested undercooked ground beef as a potential source for this outbreak. We recommended the Navy and Marine Corps retain lot information, address food handling concerns, and improve hygiene among recruits.

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