Counterimmunoelectrophoresis of synovial fluid in the diagnosis of septic arthritis.

The evaluation by counterimmunoelectrophoresis (CIE) of joint fluid for bacterial antigen from 16 children with suspected septic arthritis is reported. Joint fluid from six children contained capsular antigen of Haemophilus influenzae type b (four) or Streptococcus pneumoniae (two). One child was infected with S. pneumoniae but was positive by CIE for both H. influenzae type b and S. pneumoniae. Five of six children who were less than 2 years of age were infected with H. influenzae. Two children had negative cultures of joint fluids, and a presumptive etiology for their infection was proposed only by demonstration of bacterial antigen. CIE, which has been widely applied to cerebrospinal fluid, urine, and serum, is a helpful adjunct to the evaluation of joint fluid from children with suspected septic arthritis.