If culture negative peritonitis consider: (1) culture volume too small, (2) prior use of antibiotics, (3) unusual causes of peritonitis: mycobacteria; nocardia, fungi, including lipid-dependent yeast; Legionella spp, slow-growing/fastidious bacteria (e.g. Campylobacter spp, Ureaplasma spp, Mycoplasma spp); enteroviruses. Repeat cell count and differential, Gram stain, and culture at 3-5 days if culture negative. Consult microbiologist.