Case Presentation: A 33-year-old woman with a past medical history of a calcaneal fracture requiring internal fixation complicated by poor wound healing and repair with a free flap, and polymicrobial osteomyelitis on home amoxicillin-clavulanate and IV daptomycin presented with three days of fevers, chills, and generalized malaise. She reported adherence to her home antibiotic regimen. She was tachycardic with a pulse of 113, and her right heel had a warm, nontender free flap with intact sutures and scant oozing. Her initial white blood cell count was 6.9K/uL, which decreased to 2.3K/uL the following day. She had a lactic acid of 2.1 mmol/L, an erythrocyte sedimentation rate of 29 mm/hr, an AST 67 units/L, and ALT of 140 units/L. An MRI revealed a new 3.9 cm soft tissue fluid collection near the Achilles tendon but was otherwise unchanged from prior and suspicious for osteomyelitis. Aspiration of the fluid pocket yielded serosanguinous fluid which did not harbor any bacteria by microscopy or culture. Both the orthopedic surgeon and plastic surgeon felt that the patient’s exam and imaging was not consistent with a recurrent infection of her heel. Cultures from the peripherally inserted central catheter (PICC) grew Pantoea species, with a time to detection of 7.53 hours. Peripheral cultures grew the same, with a time to detection of 11.04 hours. The patient was diagnosed with bacteremia secondary to a central line infection, the PICC was removed, and follow up blood cultures at 72 hours demonstrated clearance of the infection. Symptoms resolved shortly after removal of the line and initiation of broad-spectrum antibiotics. She was discharged home on an oral antibiotic regimen consisting of levofloxacin and metronidazole.
Discussion: The source of infection was initially assumed to be the patient’s calcaneus, which had previously been affected by polymicrobial osteomyelitis. However, an appropriately broad initial workup led us to identify the PICC as the actual source of infection and resulted in the timely treatment of the patient. The use of a PICC for outpatient parenteral therapy (OPAT) is broadly utilized to reduce hospital length of stay, but does come with risk including infection. The organism was further identified as Mixta calida, formerly Pantoea calida. This member of Enterobacteriaceae is a plant pathogen that was also isolated from infant formula in 2010. There have been three other published case reports since 2014 of this organism as a human pathogen: post-surgical meningitis, an implantable cardioverter defibrillator infection, and bacteremia in a patient with metastatic gastric cancer. This case is the first reported Mixta calida central line infection. Our specimen was sensitive to all antibiotics tested, but there has been a report of ampicillin resistant Mixta calida. Mixta calida appears to represent a rare but rising cause of infection. The source of our patient’s exposure to this organism was not identified.
Conclusions: Use of a PICC for OPAT is common but represents an infection risk, and any patient presenting with sepsis and a PICC in place must be evaluated for a line infection. Even in patients in whom a source of infection may appear obvious, a thorough evaluation is vital to making the correct diagnosis.