Polymorphonuclear Counts in Ascitic Fluid and Microorganisms Producing Spontaneous Bacterial Peritonitis: an Under-recognized Relationship

BACKGROUND AND AIMS. In cirrhotic patients with spontaneous bacterial peritonitis (SBP) higher polymorphonuclear (PMN) count in ascitic fluid have been reported in infections caused by Gram-negative bacilli (GNB) as opposed to Gram-positive cocci (GPC). However, the influence of other associated factors on the PMN count, such as the specific microorganism causing the episode of SBP, has not been well established. METHODS. Retrospective observational study of 194 episodes of positive ascitic and/or blood culture SBP in 159 patients with liver cirrhosis (2001-2009). Parameters associated with PMN count in ascitic fluid at diagnosis were evaluated. RESULTS. The multivariate analysis (model 1) showed that a virulent etiology of the infection [coefficient 3.941 (95% confidence interval (95 CI): 0.421-7.461)] and the model for end-stage liver disease (MELD) score [coefficient 0.196 (95 CI: 0.007-0.384)] were positively associated with the PMN count in ascites, while a nosocomial acquisition was inversely associated [coefficient -3.546 (95 CI: -6.855 - -0.238)]. A nonsignificant trend toward higher PMN count was found in GNB versus GPC, but there were differences between groups of microorganisms: pyogenic streptococci [median (p25-p75): 3211 (1615-8004)], Enterobacteriaceae [2958 (917-7690)], Vibrionaceae [9215 (375-17280)], nonfermenting GNB [1384 (565-3865)], viridans group streptococci [1044 (503-2354)] and enterococci [1050 (476-4655)](p = 0.005). No clear cut-offs of ascitic PMN count predicting a particular etiology could be calculated out of these data. CONCLUSIONS. In cirrhotic patients with SBP, the causing microorganism, the place of acquisition of the infection and the host liver condition were the main factors determining PMN count in ascitic fluid. Third-generation cephalosporin resistance was associated with low PMN count probably because this group included bacteria with inherent low virulence.