INTRODUCTION: Presentation and imaging findings of acute focal bacterial nephritis, a localized renal infection not containing drainable pus, have been extensively addressed. The aim of this review was to assess the prevalence of cases without pyuria or bacteriuria and the spectrum of microorganisms underlying this condition. EVIDENCE ACQUISITION: We conducted a systematic review of the literature in the National Library of Medicine and Excerpta Medica databases. For the final analysis, we retained 54 reports published between 1981 and 2018 describing 251 patients affected by focal bacterial nephritis, who have been specifically investigated with respect to urinalysis and standard bacterial cultures. They were 177 (102 females and 75 males) subjects ≤20 and 74 (57 females and 17 males) >20 years of age. EVIDENCE SYNTHESIS: Pyuria and bacteriuria were absent in 33 cases, while pyuria was not associated with bacteriuria in 5 further cases. The vast majority of culture-positive cases were caused by Enterobacteriaceae (slightly less than 80%) and Pseudomonas species (approximately 10%). Enterococcus species and Staphylococcus aureus were isolated in slightly more than 10% of the cases. CONCLUSIONS: A large subset of patients affected by focal bacterial nephritis present without pyuria and significant bacteriuria. The initial management consists of broad-spectrum antimicrobials with high tissue penetration, active against Enterobacteriaceae, Pseudomonas species, Enterococcus species and Staphylococcus aureus.
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