An Unusual Cause of Septic Bursitis in an Adolescent

To the Editors: Septic bursitis is infrequently reported in children and is caused primarily by Gram-positive bacteria.1,2 In 1 case series, all 10 pediatric patients with septic bursitis had infections caused by Staphylococcus aureus or Streptococcus pyogenes.2 We describe the first case, to our knowledge, of septic bursitis due to Aeromonas hydrophila and Enterobacter kobei in a child. A 14-year-old male presented with 4 days of right knee swelling and pain and 2 days of fever to 38.9 °C. Four days prior, he went on a deep-sea fishing trip in the Gulf of Mexico but did not recall having any cuts or other injuries. He swims in a brackish stream near his home, cares for domestic farm animals, and traps and handles armadillos and turtles. He sustained a right knee injury 2.5 years earlier when running near a stream and was impaled with a stick. He did not seek medical attention at the time, and the wound was not explored and cleaned. Since then, the family reports that he has intermittent right knee swelling. On physical examination, he had right knee swelling, erythema and marked tenderness over the suprapatellar region. The peripheral white blood cell count was 15.4 cells/mm3, C-reactive protein was 12.4 mg/dL and erythrocyte sedimentation rate was 14 mm/h. Blood cultures were negative. Magnetic resonance imaging demonstrated a large fluid collection in the anterior thigh subcutaneous soft tissues without evidence of deep osteoarticular extension (Fig. 1). Orthopedic surgery aspirated the prepatellar bursa, and foul-smelling purulent material was obtained, prompting open incision and drainage with no foreign body found. Gram stain of the purulent material showed Gram-negative rods, and cultures grew A. hydrophila and E. kobei. The patient received intravenous cefepime and was discharged 2 days later with a 3-week course of oral ciprofloxacin. One month later, he was doing well without recurrence of symptoms.FIGURE 1.: Radiographs (A and B) and magnetic resonance imaging STIR sagittal (C) of the right knee demonstrating a large prepatellar bursa with perilesional soft tissue edema without deep extension. No knee joint effusion or marrow edema to suggest osteomyelitis.The genera Aeromonas and Enterobacter consist of facultatively anaerobic, Gram-negative bacilli. Both Aeromonas spp. and Enterobacter spp. are ubiquitous opportunistic pathogens that are found in a wide variety of environmental habits and Aeromonas spp. are especially associated with fresh or brackish water sources.3,4A. hydrophila, the species isolated from our patient, is one of the principle Aeromonas species causing disease in humans and has been associated with posttraumatic skin and soft tissue infections with a history of water exposure. In addition to A. hydrophila, our patient also had E. kobei isolated from his operative culture. Enterobacter species belong to the “ESKAPE” group and are increasingly of concern due to their heightened level of resistance across different classes of antibiotics including frequent expression of extended-spectrum β-lactamases.5 Fortunately for our patient, both his Aeromonas and Enterobacter isolates maintained susceptibility to fluoroquinolones, and he was able to transition to definitive therapy with oral ciprofloxacin. Clinicians should maintain a high degree of suspicion for polymicrobial infections in patients with soft tissue injury after water exposure. Additionally, due to variable resistance patterns, antibiotic susceptibility testing should inform antibiotic therapy selection for infections due to Gram-negative water-related pathogens.