Late-onset group B streptococcal septic arthritis in an afebrile neonate: a case report

The majority of neonatal group B streptococcal (GBS) infections present as sepsis or meningitis, while osteoarticular involvement is rare during the neonatal period. We report a case of culture-confirmed late-onset GBS septic arthritis in a 26-day-old male neonate presenting with progressive swelling, erythema, and irritability of the left knee without fever. Surgical irrigation and debridement revealed purulent arthritis. Because maternal prenatal records, maternal GBS screening status, and maternal infectious disease history were unavailable, a catheterized urine polymerase chain reaction (PCR) panel for sexually transmitted infections and genital tract-associated pathogens was obtained during the evaluation of a possible vertically or perinatally transmitted infection. The panel was positive for GBS on hospital day 0, approximately 72 h before joint tissue culture confirmation. Joint tissue culture subsequently yielded GBS, while blood and cerebrospinal fluid cultures remained sterile. The patient was treated successfully with intravenous ampicillin after initial empiric therapy with ampicillin and gentamicin. Clinical recovery and ultrasonographic resolution of joint effusion were achieved, and no clinical sequelae were detected at the 3-month post-discharge follow-up. This case emphasizes that afebrile neonates with progressive monoarticular swelling should be evaluated for septic arthritis and that definitive diagnosis relies on microbiological confirmation from a sterile-site specimen. The urine PCR finding, in this case, is reported as a hypothesis-generating observation in a neonate with unavailable maternal screening data; however, its biological significance remains uncertain and should not be interpreted as validation of urine PCR for invasive neonatal GBS disease or septic arthritis.