Comparison of the characteristics of culture-negative versus culture-positive septic arthritis in children.

Corresponding author: Dr. Nan-Chang Chiu, Department of Pediatrics, Mackay Memorial Hospital, 92, Section 2, Chung Shan North Road, Taipei 104, Taiwan. E-mail: ncc88@ms2.mmh.org.tw Septic arthritis is an infection for which long-term antibiotic therapy is recommended [1,2]. Successful treatment of septic arthritis in children depends on early recognition and prompt institution of therapy, including appropriate antibiotic choice and length of therapy [3]. Thus, identification of the causative pathogen is important for selecting an appropriate antibiotic in patients with septic arthritis. When a pathogen cannot be demonstrated, however, empiric therapy is needed. An etiologic diagnosis is sought by culturing joint fluid obtained by aspiration or surgical drainage, although blood cultures sometimes yield the pathogen [4]. However, the pathogen cannot be identified in around 20-40% of cases of septic arthritis [1,5-7]. The purpose of this study was to compare the natural history, clinical presentation, laboratory results, treatment course and outcome of children with culture-negative and culture-positive septic arthritis. Septic arthritis in children can be difficult to diagnose and may be associated with severe morbidity. A majority of apparent septic arthritis cases may have negative culture, thereby creating a dilemma regarding treatment. The medical charts of 209 children with the diagnosis of septic arthritis were retrospectively reviewed to evaluate the differences between culture-negative (n = 64) and culture-positive (n = 145) cases. Demographic data, clinical manifestations, treatment, and outcome were analyzed. Laboratory data recorded included white blood cell count, erythrocyte sedimentation rate, C-reactive protein, imaging studies, and culture results. Patients with culturenegative arthritis had a significantly lower incidence of fever (56.3% vs 70.3%, p=0.047), local pain or tenderness (42.2% vs 69.7%, p=0.0001), changes in the overlying skin (45.3% vs 62.1%, p=0.024), motion limitation (25.0% vs 42.8%, p=0.014), and osteomyelitis (25.0% vs 40.7%, p=0.029). Culture-negative patients had a longer duration of symptoms or signs before diagnosis (10.1 ± 8.9 days vs 6.5 ± 5.7 days, p=0.046) and a shorter antimicrobial course (24.5 ± 5.1 days vs 35.7 ± 8.1 days, p=0.001). Children with culture-negative septic arthritis had a lower prevalence of residual joint dysfunction at 6 months after treatment (3.1% vs 11.7%, p=0.046). In conclusion, children with culture-negative septic arthritis have milder clinical manifestations, earlier response to treatment, and a better outcome than those with culture-positive disease.