The culture negative peritonitis rate should be no more than 20% of all episodes. Culture negative episodes may be due to recent antibiotic use for a non-peritonitis indication or related to culture technique (discussed in the ISPD Peritonitis Recommendations: 2016 Update on Prevention and Treatment.  Li et al. Perit Dial Int. 2016 Sep 10;36(5):481-508).
If the cultures are negative at day 3 and the peritonitis is resolving, the recommendation is to discontinue gram negative coverage, and continue gram positive coverage for a total of 2 weeks. If it not, the ISPD guidelines recommend special culture techniques for the isolation of unusual organisms such as mycobacteria species, Nocardia, and Legionella.  Catheter removal should strongly be considered for culture negative peritonitis episodes that fail to respond by day 5.  With respect to outcomes, culture negative peritonitis is typically low risk with resolution of almost 90% of all episodes and a catheter removal rate of about 8-10% (Mujais Kidney Int Suppl. 2006 Nov;(103):S55-62).