Severe and Progressive Cellulitis Caused by Serratia marcescens Following a Dog Scratch

Soft tissue infections occur in over 30% of patients with chemotherapy-induced neutropenia. Gram-positive bacterial infections predominate early in neutropenia, and likelihood of infection by resistant bacteria and fungi increases with prolonged neutropenia. Prior infections and exposures influence the risk of rare pathogens. A 55-year-old woman with chemotherapy-induced neutropenia was scratched on her forearm by a dog. She cleaned the wound with isopropanol and was treated empirically with amoxicillin-clavulanate. Over the next 4 days, she developed fever along with erythema, edema, and mild tenderness of the forearm without purulence or crepitus. She was hospitalized and received empiric treatment with intravenous vancomycin, piperacillin-tazobactam, tobramycin, and voriconazole. Despite therapy, her fevers persisted and the cellulitis progressed for over a week. After 10 days of hospitalization, her neutrophil count began to recover and a bulla developed at the wound site. Culture of the bullous fluid grew Serratia marcescens, and antibiotics were switched to cefepime based on susceptibility. She defervesced and showed substantial improvement of cellulitis within 48 hours and was discharged on oral ciprofloxacin. Serratia marcescens skin infections are rare, and this may be the first report of Serratia cellulitis associated with trauma from dog contact. This case highlights the need to consider unusual pathogens based on exposure history and immune status and to obtain cultures from fluid collections or tissue in cases of treatment-resistant soft tissue infections.