Significance of circulating capsular antigen in Klebsiella infections.

Klebsiella capsular antigen (KCA) was detected in serum by counterimmunoelectrophoresis in 8 of 31 patients with klebsiella bacteremia, in two nonbacteremic patients with pneumonia and meningitis, respectively, and in the cerebrospinal fluid only of 1 of the 31 bacteremic patients. It was also detected in cerebrospinal fluid, urine (two patients each) empyema fluid, and abscess drainage (one patient each). Patients whose bacteremias were associated with a discernible tissue focus (e.g., pneumonia) tended to have detectable serum KCA more often than those with "primary bacteremia." A fatal outcome occurred in six of nine bacteremia patients with detectable serum KCA compared with 4 of 22 without demonstrable antigen (P < 0.05). Persistent antigenemia and antigenuria aided in the diagnosis of perinephric abscess in one patient, and increasing levels of serum KCA anticipated treatment failure in another patient with pneumonia. The presence of detectable KCA in the serum of patients infected with klebsiella thus appeared to correlate with severity of infection, with persistence of active foci, and with a poorer prognosis than in those patients who had no detectable antigen. Whether the presence of this antigen itself plays any pathogenic role needs to be further clarified.