The Case: A 10 day old with elbow swelling, found to have a septic joint.

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Discussion: This case highlights the challenging dilemma of infants with focal source of infection and how much of a work up is needed. Bone and joint infections in neonates is rare so it is unknown how many have associated bacteremia or meningitis. Infectious disease and hospitalist colleagues will often recommend or request blood, urine and CSF studies prior to starting these infants on antibiotics.

Dr. Ren highlighted a this study from our own patient population that looked at over 500 infants <60 days old presenting with skin and soft tissue infections. The majority (63%) had blood cultures sent, 38% had urine cultures, and 27% had CSF cultures sent. Four percent of the blood cultures were positive and there was 1 case of missed bacteremia. None of the urine or CSF cultures were positive and there were no known missed UTIs or meningitis.

In cases of infants born to GBS negative mothers, young infants can also acquire GBS from colonized household contacts and go on to develop bacteremia, meningitis, or other focal infections. As Drs Agrawal and Breslin pointed out, maternal transmission is associated with early onset GBS and typically presents in the first week.  According to Red Book, late-onset GBS infection manifests as septic arthritis and osteomyelitis in approximately 5% of cases. GBS septic arthritis typically presents acutely and most commonly involves a lower extremity with a mean age of onset 20 days. GBS osteo is more insidious and presents at an older age (mean age of onset 31 days). Rates of both have decreased over the past 20-30 years with intrapartum antibiotic prophylaxis becoming standard of care.

Denouement: The patient was admitted to the NICU and taken to the OR the following day for joint washout. Joint cultures ultimately grew group B strep (blood, urine, and CSF culture were negative).  Patient was transitioned from Oxacillin/Gentamicin to penicillin once culture speciated. Discharged home on cephalexin for a total 3 week antibiotic course.

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