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BackgroundSkin and soft-tissue infections (SSTIs) are a common complication of military training. Naval Special Warfare (NSW) training requires prolonged periods of extreme physical exertion and unique environmental exposures, including extended immersion in ocean water. A centerpiece of SEAL training is referred to as “Hell Week” (HW), a colloquial term to reflect the intense physical obstacles and exposure to extreme environmental conditions endured by candidates. Due to such environmental exposures, NSW trainees are at increased risk for SSTI due to uncommon organisms. A prior outbreak of Shewanella SSTI and bacteremia among NSW trainees led to the initiation of prophylactic doxycycline 100 mg daily during and for 7 days after HW to attempt to reduce this risk. The efficacy of this intervention is undetermined.MethodsDoxycycline prophylaxis was initiated in August 2015. We conducted a retrospective analysis of SSTI incidence presenting for medical attention among NSW trainees from April 2013 to November 2018, using case records collected prospectively at the Naval Special Warfare Center. The incidence of SSTI was calculated based on the size of a given class and the number of affected trainees. SSTI cases were then divided and analyzed as occurring during vs. after HW.ResultsThe pre-intervention cohort consisted of 1626 NSW trainees. A total of 76 trainees developed SSTI, with 20 cases during HW and 56 cases in the post-HW period. In the post-intervention cohort, 2022 trainees experienced a total of 81 cases of SSTI during HW and 83 in the post-HW period. 45% of all SSTI cases occurred in the months of June, July, and August. The incidence of cellulitis between the pre- and post-intervention cohorts during HW was 2% and 4%, respectively, and 5% and 6.4% in the post-HW period. There were no hospitalizations for invasive gram-negative infections following the initiation of doxycycline prophylaxis.ConclusionDoxycycline prophylaxis does not appear to reduce the incidence of SSTI but may reduce the incidence of certain severe infections. The choice of antibiotic prophylaxis and dosing may require further investigation. Seasonality of SSTI among NSW trainees is an unexpected finding and may provide valuable information for the prevention of future illness. Disclosures All authors: No reported disclosures.

Background Several severe cases of SSTIs caused by salt-water associated Gram-negative pathogens (mainly Shewanella algae) among U.S. Naval Special Warfare (NSW) trainees prompted introduction of doxycycline prophylaxis during the highest risk portion of training, “Hell Week”. We present analysis of this intervention’s impact on disease incidence and hospital admission for serious SSTI. Necrotizing fasciitis caused by Vibrio harveyi in an NSW trainee during “Hell Week” prior to introduction of doxycycline prophylaxis. Methods We performed a retrospective cohort study examining data from hospital admissions for SSTI in trainees between 2013-2020. We assessed hospital admission rates for SSTIs, hospitalization rates per SSTI diagnosed at the clinic level, overall rates of SSTI, length of hospital stays and blood and wound culture data. We then compared data from pre- and post-intervention cohorts. Results 3371 NSW trainees participated in “Hell Week” training during the study period with 284 SSTIs diagnosed overall, 29 of which led to hospital admission. After introduction of doxycycline prophylaxis, admission rates for SSTI decreased from 1.37 to 0.64 admissions per 100 trainees (p=0.036). Overall SSTI rates diagnosed at the clinic level remained stable from 7.42 to 8.86 SSTI per 100 trainees (p=0.185). Hospitalization rates per diagnosed SSTI decreased from 18.4% to 7.2% (p=0.009). Average length of hospitalization decreased from 9.01 days to 4.33 days (p=0.034). Blood and wound culture data showed a notable decrease in SSTI from salt-water associated Gram-negative rods (Shewanella algae and Vibrio spp.). Total number of SSTI diagnosed at Naval Special Warfare Center (NSWCEN) medical clinic each “Hell Week” training period with corresponding percentage of NSW trainees diagnosed with SSTI in each class. Date of doxycycline prophylaxis initiation labeled for reference. Wound and blood culture (Cx) data from the pre-intervention and post-intervention cohorts Conclusion Doxycycline prophylaxis during “Hell Week” training for NSW trainees was associated with decreased frequency and severity of hospitalization for SSTI, as well as near elimination of infection with invasive salt-water associated pathogens. Disclosures All Authors: No reported disclosures.