448. Impact of Doxycycline Prophylaxis on Skin and Soft-Tissue Infection Incidence in Naval Special Warfare Trainees

BACKGROUND: Skin 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. METHODS: Doxycycline 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. RESULTS: The 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. CONCLUSION: Doxycycline 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. [Image: see text] DISCLOSURES: All authors: No reported disclosures.