Peritonitis due to Staphylococcus Aureus: An Unusual Complication of Pediatric Renal Abscess

Abstract

Staphylococcus aureus causes intra-abdominal infections primarily due to hematogenous seeding. Abscesses in retroperitoneal organs, and specifically renal abscesses are rare complications of staphylococcal bacteremia in children as compared to osteomyelitis, or septic arthritis. We report a case of a ruptured staphylococcal renal abscess in a child without renal anomalies that presented as clinical peritonitis in order to underscore this potentially elusive diagnosis.

Keywords: Staphylococcus aureus; Peritonitis; Renal abscess

Introduction

Retroperitoneal abscesses present a diagnostic challenge in young children because symptoms are often indolent and poorly localized manifesting a wide spectrum of presentations from fever and flank pain and limp to overwhelming sepsis [1]. In a study spanning 10 years in a tertiary center, 45 pediatric patients were identified with Computerized Tomograpghy (CT)-proven renal abscess. Of note, 43% of the patients had known vesico-uretral reflux [2]. Other risk factors associated with renal abscesses are damaged kidneys, diabetes mellitus, immunocompromised status and renal calculi [3,4].

Primary renal abscesses which present as corticomedullary involvement on imaging, are most commonly associated with ascending urinary tract infection, caused by gram negative organisms [5]. In contrast, the renal “carbuncles” in children with a healthy urinary tract are thought to result from bacteremia from a primary focus of infection elsewhere and are caused mainly by Staphylococcus aureus [4,5]. A meticulous history taking might reveal a source of infection such as a skin wound, that occurred 1-8 weeks before the abscess formation in the kidney, but many times a port of entry is not apparent [5]. We present a patient with a rare complication of a staphylococcal renal abscess.

Case Presentation

A previously healthy one year old male was admitted to the hospital with complaints of a three day fever, watery diarrhea up to 6 times a day and multiple vomiting episodes. There was no history of trauma. He was born at term after a normal pregnancy. Before the current admission, he received three doses of amoxicillin due to fever, without improvement. Upon admission the child had a 38.8 c temperature, pulse of 186 beats per minute, a respiratory rate of 40 breaths per minute and 96% oxygen saturation in room air. On physical examination he was severely dehydrated. Laboratory tests showed hemoglobin 10 mg/dl, leukocytes 37x103 cells/mm3 with 13% stab forms, elevated urea 73mg/dl (age adjusted norm 17-43) and creatinine 0.75mg/dl (age-adjusted norm 0.2-0.4). Stool was watery with no leukocytes.

He was treated with fluids and ceftriaxone in the pediatric ward with a presumptive diagnosis of occult bacteremia. The following day, the child was admitted to the pediatric intensive care unit as a result of deteriorating renal function which manifested as oliguria, weight gain of 1.4 kg and peripheral edema. His respiratory rate decreased to 15 per minute and saturation dropped to 78.6% in room air. Blood pressure dropped to 95/54mm Hg. Laboratory examination showed hemoglobin 7.9mg/dl, a rising peripheral leucocyte count, thrombocytopenia of 75x103. Schistocytes were seen on peripheral smear. Impending renal failure due to Hemolytic-Uremic syndrome was suspected and emergent peritoneal dialysis was attempted. Upon introduction of the dialysis catheter, a cloudy peritoneal aspirate was observed. The fluid contained 13.6x103cells, of which 90% were polymorphonuclear cells. Blood, stool, and urine cultures were negative. Empiric treatment was initiated with ceftriaxone and metronidazole on the suspicion of a perforated viscus. The next day the culture from the peritoneal fluid was positive for oxacillin sensitive Staphylococcus aureus. Therapy was changed to cefazoline and gentamicin. An abdominal CT demonstrated a laceration in the upper pole of the right kidney which transversed the cortex extending to a high-density fluid area involving the Morrison pouch and compressing the kidney (Figure 1). CT-guided percutaneous drainage was performed and 3ml of yellow pus was aspirated. Staphylococcus aureus with the same sensitivity as from the peritoneal fluid was cultured from the exudate. On day 7 of admission, blood cultures were sterile, trans-thoracic echo was negative for vegetations, and bone scan was negative for osteomyelitis. However, the patient remained febrile. A second aspiration was performed and Staphylococcus aureus grew from the drain that was placed during the procedure. The third CT guided aspiration performed on day 18 was sterile, after which the patient became afebrile. The patient was discharged from the hospital in good condition after 21 days of intravenous antibiotic therapy with instructions to continue oral cephalexin for 10 more days. Follow-up Dimercaptosuccinic acid (DMSA) isotope scan after four months was recommended by nephrological consult to rule out a renal scar. Immunologic consultation was obtained because of an invasive staphylococcal infection at an early age, and neutrophile function studies including super-oxide generation, chemotaxis and phagocytosis were normal. Blood immunoglobulin levels were normal as well.

    

    

    Figure 1:  Abdominal computed tomography, childhood protocol, shows a
right renal abscess with rupture into the perirenal space with involvement of
the Morrison pouch.