A case report of Mycobacterium fortuitum infection after muscle injection

Rationale: Injection-related abscesses are a common complication in clinical practice, but the identification of infected bacteria might be difficult.Patient concerns: A 51-year-old female patient was admitted to the hospital due to a lump on her right buttock that emerged after receiving intramuscular injections to treat left shoulder joint pain. The lump gradually enlarged into a 3.0 to 4.5 cm mass at the time of admission with symptoms such as skin redness, itching, and pain.Diagnoses: The patient received ultrasonic and other laboratory examinations. Laboratory results from the drainage indicated that the infection was caused by a rapidly growing mycobacteria and was confirmed as Mycobacterium fortuitum by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry.Interventions: The patient was treated with antibiotics for 12 days after incision and drainage of the abscess in the right buttock. Local dressings were changed regularly. A migration lesion that appeared 3 days after treatment was drained and cleaned when it matured.Outcomes: The lesion substantially decreased in size and the patient was discharged after 2 months of treatment.Lessons: Rapidly growing mycobacteria are rare but important pathogens that should be considered in patients with injection-related abscesses. Early identification and appropriate treatment can result in a favorable prognosis.