Streptococcus pneumoniae, the principal cause of otitis media, sinusitis, and pneumonia, may also cause intraabdominal infection. Most common is primary peritonitis, occurring without a documented source of infection elsewhere. When such infection appears as a complication of preexisting ascites, organisms probably reach the peritoneal cavity by translocation from the bowel. Peritonitis in the absence of prior peritoneal disease almost always occurs in females. In such cases, it is highly likely that organisms reach the peritoneal cavity by migration via the female genital tract; clinically recognizable infection of the genital organs may be present or absent. Actual hematogenous dissemination of organisms from an infected focus does not play a prominent role, as shown by the extraordinary rarity of peritonitis in patients with recognized pneumococcal bacteremia. Pneumococci also cause infection of, or adjacent to, an organ of the digestive tract. Infection of the stomach occurs in the presence of prior damage to the mucosa such as alcoholic gastritis, an ulcer, or surgery. In appendicitis, pneumococci may be found with typical colonic flora or as the sole isolate. Biliary disease has also been documented despite the fact that susceptibility to lysis by bile is an identifying characteristic of S. pneumoniae. The infrequency of these conditions is consistent with the fact that pneumococcus does not generally escape the lethal effect of gastric acid and/or bile; when it does, because of a relatively low-grade pathogenicity for bowel, it requires the presence of another abnormality or abnormalities in order to cause disease. Colonization of the bowel is likely to be the source of organisms in primary pneumococcal peritonitis as well.
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