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Although many species of bacteria are known to retain viability while in ordinary cell suspensions and when very dry as after lyophilization, little is known of the effects of changes in water content at intermediate states. Two mechanisms of loss of viability may operate during a change in wetness. The two discussed here will depend in opposite ways upon the rate of change of water content. On the one hand, death may be due to D)rv air 15% RH Water vapor under vacuulm 29% RH Water vapor uinder vacuum 50% RH Water vapor under vaCuum 70% RH 94% RH Water injected Water injected Water injected Water injected Water injected Water injected Water injected Water injected Water injected Water injected Water injected

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A simple derivation of the perfect focusing properties of the trochoidal type mass spectrometer, which leads to convenient methods of correlating the many variables for design purposes, is given. Nomographs and general trochoids are given which apply to charged particles in crossed, uniform, electric, and magnetic fields.

BackgroundShiga toxin-producing Escherichia coli (STEC) infections are a major cause of foodborne illness and the principal cause of hemolytic-uremic syndrome (HUS). In November 2017, CDC and the US Navy responded to an outbreak of STEC illnesses in military recruits at the Marine Corps Recruit Depot in San Diego (MCRD). We investigated to determine the source of this outbreak and identify prevention and mitigation measures.MethodsIn October 2017, medical staff 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 defined as confirmed (PFGE-confirmed STEC infection matching outbreak strains), probable (diagnosis of HUS and/or CIDT evidence of STEC), or suspected (bloody diarrhea). We conducted environmental evaluations of dining 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.ResultsWe identified 64 confirmed, 105 probable, and 91 suspected case-patients. Thirty case-patients required hospitalization and 15 had HUS. Ages ranged from 17 to 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 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 dining facility records did not document the dates on which specific lots of ground beef were used.ConclusionCase–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.Disclosures All authors: No reported disclosures.