A 15-year-old girl was admitted to the hospital because of mild abdominal pain and fever up to 37.8°C of 2-day duration. Specifically, she developed peri-umbilical abdominal pain that gradually moved to the right lower abdominal quadrant. In addition, she vomited twice on the day of admission. Her past medical history was unremarkable. She was not receiving any medications.

Physical examination on admission showed temperature 38°C, respiratory rate 14 breathes/min, arterial blood pressure 120/70 mm/Hg, and heart rate 84 beats/min. There was mild tenderness during the palpation of the right lower abdominal quadrant. There was no rebound tenderness or abdominal wall rigidity. The rest of the examination was normal.

Routine laboratory testing on admission revealed increased leucocytes (12,360 white blood cells per mm3 of peripheral blood, 86.3% neutrophils). Liver function tests and serum creatinine, urea, electrolytes, and glucose were normal. An abdominal ultrasound showed small amount of fluid in the Douglas pouch.

The patient received intravenous metronidazole 500 mg every 8 hours and tazobactam/piperacillin 4/0.25 gr every 8 hours after her admission to the hospital. Appendicitis was considered as the most likely diagnosis. The patient underwent laparoscopic appendectomy 40 hours after her admission. No transfusion of blood products was needed. The intra-operative findings were consistent with inflammation of the appendix (erythema and edema). In addition, a small amount of cloudy fluid was seen in the Douglas pouch.

Despite the operation, the patient continued to have fever and rigors. In fact, a gradual increase of the body temperature was noted during the post-operative period. There was no evidence from the physical examination and the laboratory and imaging testing for any of the likely causes of post-operative fever such as respiratory or urinary tract infection, post-operative wound infection, atelectasis, deep venous thrombosis, and drug fever.

Klebsiella pneumoniae was isolated from cultures of blood specimens, which were taken for first time during the second post-operative day. The pathogen was resistant to 1st, 2nd, and 3rd generation cephalosporins, quinolones, piperacillin/tazobactam, and aztreonam, intermediately susceptible to meropenem (mean inhibitory concentration, MIC = 8 mg/l), and susceptible to gentamicin and colistin. Cultures of urine specimens did not grow any micro-organisms. Chest and abdominal x-rays, abdominal ultrasound, as well as computed tomography (CT) scan of the chest and upper and lower abdomen, a transthorasic echocardiogram, ultrasound triplex testing of the intra-abdominal arteries and veins as well the lower extremities veins, and a gallium nuclear medicine scan did not reveal any abnormal findings.

The patient continued to have high fever (up to 39.8 °C), sweating, malaise, and persistent isolation of Klebsiella pneumoniae from blood specimens, despite the administration of various antimicrobial regimens, including the use of intermittent intravenous gentamicin (60 mg every 8 hours), meropenem (1g every 8 hours), and colistin (1.000.000 units every 8 hours).

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