Primary Pneumococcal Peritonitis can be the first presentation of a familial complement factor I deficiency.

Primary pneumococcal peritonitis is a rare infection that has been described in women but has not been previously linked with immunodeficiency. The complement system plays a central role in immune defense against Streptococcus pneumoniae and, in order to evade complement attack, pneumococci have evolved a large number of mechanisms that limit complement mediated opsonization and subsequent phagocytosis.We investigated an apparently immunocompetent woman with primary pneumococcal peritonitis and identified a family with deficiency for complement factor I. Primary pneumococcal peritonitis should be considered a possible primary immunodeficiency presentation.