Low prevalence of complement deficiencies among patients with meningococcal disease in Norway.

Sera from 98 individuals who had survived meningococcal disease were analysed for classical and alternative pathway haemolytic activity and the complement components C3, C4 and properdin. No complete deficiency was found. However, median properdin concentration was only 86% in the disease group compared with the controls (P < 0.001). Properdin was also significantly lower in serogroup C disease (median 76%) compared with serogroup B disease (median 90%, P = 0.005). Severe properdin deficiency is an established risk factor for meningococcal disease. The present data may indicate that even moderately reduced properdin level can increase the risk of developing meningococcal disease.