Sir.—We read with interest the article by Freij et al.1 Primary peritonitis may be defined as an acute inflammatory process of the peritoneal cavity without a demonstrable intra-abdominal source. As noted by the authors, other studies have demonstrated that bacterial cultures of the peritoneal fluid are negative in 25% to 35% of cases of primary peritonitis. Although we agree with the authors' speculation of the possibility of a viral cause in a small percentage of these patients, we would like to suggest that other causal agents, such as Yersinia species, might be implicated in the pathogenesis of primary peritonitis.
Niléhn,2 in 1967, reported the isolation of Yersinia enterocolitica from appendiceal cultures of 21 of 581 patients undergoing appendectomy for suspected appendicitis. Most of these patients included otherwise healthy children and young adults. Of the cases of histologically confirmed appendicitis, Y enterocolitica was recovered from only 0.6%. In