Acute Focal Bacterial Nephritis and Bacteremia Due to Staphylococcus simulans Following an Upper Respiratory Infection in a Child: A Case Report.

Coagulase-negative Staphylococcus (CoNS) is a rare cause of UTIs in children and is often regarded as a contaminant in urine samples. We report a case of acute focal bacterial nephritis (AFBN) and bacteremia caused by Staphylococcus simulans following an upper respiratory infection in a pediatric patient. The patient, a four-year-old girl, presented with fever, cough, and a runny nose two days before being referred to our hospital due to persistent fever and poor oral intake. A multiplex nested PCR test of a nasopharyngeal swab sample detected human rhinovirus/enterovirus. Urinalysis showed no leukocyte esterase or nitrites, but revealed 1-4 white blood cells/high-power field and 1+ bacteria. Despite these findings, S. simulans was isolated from both urine and blood cultures. Contrast-enhanced abdominal CT revealed multifocal hypodense, wedge-shaped space-occupying lesions in both kidneys, characteristic of AFBN. This case underscores that S. simulans can cause severe UTIs and highlights the importance of considering CoNS, including S. simulans, as a potential UTI pathogen. The results of urine cultures should be interpreted in conjunction with other clinical findings, even when an alternative diagnosis for fever is present.