Shewanella algae Infection in United States Naval Special Warfare Trainees

Background: Shewanella algae is a motile Gram-negative bacillus and ubiquitous marine microorganism that is an uncommon cause of human disease. Naval Special Warfare (NSW) trainees undergo unique physiologic stresses that include prolonged immersion in marine water, most notably during a continuous five-day operational exercise on land and sea with minimal sleep, arduous conditions including poor sanitation and hygiene (“Hell Week”). As such, they may be uniquely vulnerable to disease from this pathogen. Herein, we describe the clinical syndromes and outcomes of Shewanella infection in NSW trainees.

Methods: We retrospectively reviewed all cases of Shewanella spp. infections at Naval Medical Center San Diego between 2012-2015.

Results: Five patients were identified with clinical cultures demonstrating Shewanella algae consisting of one positive blood culture and five unique wound cultures. All isolates were sensitive to ceftriaxone, levofloxacin, piperacillin/tazobactam, trimethoprim-sulfamethoxazole, gentamicin and meropenem. The patients were all male between the ages of 21 to 26. All of the patients had no prior comorbidities and were otherwise healthy prior to starting NSW training. Four of the five patients had recently completed Hell Week, and all four presented with skin and soft tissue infections (SSTI). Two of the four patients with SSTI had concomitant bacteremia: one patient with cellulitis and Shewanella bacteremia, and another patient with a polymicrobial lower extremity necrotizing fasciitis and septic shock with Shewanella and Vibrio harveyi in the wound and V. harveyi bacteremia. The fifth patient presented after a ruptured tympanic membrane following an eighteen foot dive and subsequently developed otitis media. All patients responded to debridement, if appropriate, and systemic antimicrobial therapy.

Conclusion: Shewanella algae may cause invasive and potentially life-threatening infection in immunocompetent hosts, including otherwise-healthy NSW trainees in the setting of prolonged physiologic stress. Active surveillance is ongoing to monitor for Shewanella spp. infections in this population. Mitigation strategies are needed to minimize the risk of disease from rare pathogens in demanding military environments.