BACKGROUND: The appropriate duration of antimicrobial therapy for febrile urinary tract infection (fUTI) in children has not been established. This study examined the optimal duration of treatment for fUTI in children.
METHODS: We created a protocol that used fever duration to determine the duration of antibiotic administration. Transvenous antibiotics were administered until 3 days after resolution of fever, followed by oral antibiotics for 1 week. Diagnosis of fUTI was based on a fever of 37.5°C or higher and a quantitative culture of catheterized urine yielded a bacteria count of ≥5 × 104. Acute focal bacterial nephritis (AFBN) and pyelonephritis (PN) were diagnosed on the basis of contrast-enhanced computed tomography (eCT) findings. We retrospectively reviewed treatment outcomes.
RESULTS: Of the 78 patients treated according to our protocol, data from 58 were analyzed-49 children (30 boys) had PN and nine (three boys) had AFBN. Blood test results showed that patients with AFBN had significantly higher white blood cell counts and C-reactive protein levels than did those with PN; however, urinary findings and causative bacteria did not differ between groups. Time to resolution of fever and duration of intravenous antibiotic administration were significantly longer in patients with AFBN than in those with PN. However, average duration of AFBN treatment was 14.2 days, which was shorter than the previously reported administration period of 3 weeks. No recurrence was observed in AFBN patients.
CONCLUSIONS: A protocol that used fever duration to determine the duration of antimicrobial treatment was useful. Invasive examinations, such as eCT, were not required.

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Acute focal bacterial nephritis (AFBN) is characterised by a complicated upper urinary tract infection ranging from acute pyelonephritis to renal abscess. Timely diagnosis of AFBN is important because antibiotic therapy of longer duration is required. A 10-year-old boy presented with fever for 5 days and bilateral flank pain. He was oriented and cooperative but appeared ill. Physical examination did not reveal any oedema or costovertebral angle tenderness. Acute phase reactants such as erythrocyte sedimentation rate and C-reactive protein were raised, serum creatinine was 1.25 mg/dL (0.31-0.88) and leucocyte esterase was positive in the urine. Ultrasonographic examination demonstrated bilaterally enlarged kidneys with increased echogenicity. Because of the high creatinine level, abdominal magnetic resonance imaging (MRI) was performed instead of computed tomography (CT) for further evaluation. The MRI showed an increase in the size of both kidneys, renal cortical heterogeneity and multiple cortical nodular lesions with diffusion restriction (constrained Brownian movement of water molecules) on diffusion-weighted MRI. A negative urine culture result in children presenting with fever and abdominal pain may mislead the clinicians, causing them to miss a nephro-urological diagnosis. It is therefore recommended that patients in whom the cause of fever cannot be determined be scanned by ultrasound and examined by CT or MRI so that undiagnosed and/or suspected cases of AFBN might be detected.

OBJECTIVE: To evaluate the association between the incidence of renal scarring on technetium-99 m dimercaptosuccinic acid (DMSA) renal scintigraphy and the severity of renal parenchymal infections, such as acute pyelonephritis (APN), acute focal bacterial nephritis (AFBN), and renal abscess, based on computed tomography (CT) diagnosis.
METHODS: Sixty-one children with renal parenchymal infections were included and classified into two groups: those with (renal scarring group) and without renal scarring (non-renal scarring group) on chronic-phase DMSA renal scintigraphy. The severity of renal parenchymal infection was classified into three grades using CT: APN, AFBN, and renal abscess as grades 1, 2, and 3, respectively. The severity of renal parenchymal infection, vesicoureteral reflux (VUR) grade, and intrarenal reflux occurrence during voiding cystourethrography (VCUG) were evaluated between the renal and non-renal scarring groups. Fisher\'s exact test and Mann-Whitney U test were used for statistical analysis.
RESULTS: Renal scars were detected in 28 (45.9%) of the 61 patients. We found that 2/9 (22.2%), 18/41 (43.9%), and 8/11 (72.7%) patients with APN (grade 1), AFBN (grade 2), and renal abscess (grade 3) had renal scarring, respectively. There was a significant difference in the grade of severity of renal parenchymal infection between the renal (median = 2 [interquartile range, 2-3]) and non-renal (median = 2 [interquartile range, 2-2]) scarring groups (p = 0.023). There was a significant difference in the grade of VUR between the renal (median = 3 [interquartile range, 0-4]) and non-renal (median = 0 [interquartile range, 0-2]) scarring groups (p = 0.004). No significant difference in intrarenal reflux occurrence was observed between the renal (present/absent: 3/25) and non-renal (present/absent: 0/29) scarring groups (p = 0.112).
CONCLUSIONS: Our results showed that pediatric patients with renal scarring on chronic-phase DMSA renal scintigraphy tended to have a more severe renal infection.

A toddler girl presented to our hospital with a fever that lasted for five days. She had no prior history of urinary tract infections or contact with farm animals. Investigations revealed a diagnosis of acute focal bacterial nephritis (AFBN), and we initiated antimicrobial therapy with ampicillin and cefmetazole. On day five, methicillin-resistant coagulase-negative staphylococci were detected in her urine culture, and we changed the antibiotics to vancomycin. Antibiotic therapy was continued for 21 days, with no recurrence of fever. Finally, the bacteria were identified as Staphylococcus (S.) simulans, which is a common farm animal pathogen. Clinicians should be aware of the possibility of AFBN caused by S. simulans, even if the patient has no prior history of close contact with farm animals. If a rare organism is detected in urine culture during AFBN treatment, the patient should be treated with appropriate antibiotics for the pathogen.

Renal leukemic infiltration is uncommon in myeloid neoplasms, including myelodysplastic syndromes (MDS). A 76-year-old male patient was admitted to our hospital with complaints of fever and dyspnea. He was diagnosed with MDS with multilineage dysplasia and acute focal bacterial nephritis (AFBN) based on clinical, laboratory, and radiological investigations. Antibiotic treatment temporarily improved his condition, but the radiological image of AFBN remained. His condition gradually deteriorated into multiple organ failure, and he unfortunately died on the 31st day of hospitalization. Autopsy findings revealed significantly increased p53-positive blasts in the bone marrow and renal parenchyma overlapping AFBN, suggesting leukemic transformation and renal infiltration. This case emphasizes the need to review the diagnosis when antibiotic treatment is ineffective in MDS patients with AFBN.

Staphylococcus saprophyticus is a gram-positive, coagulase-negative member of the Staphylococcus genus and is second only to Escherichia coli as a cause of urinary tract infections in the young female population. S. saprophyticus usually has good susceptibility to drugs commonly used to treat urinary tract infections, but it is often methicillin-resistant. Here we report a case of acute focal bacterial nephritis in a 13-year-old female patient caused by methicillin-resistant S. saprophyticus and treated with daptomycin (DAP). The patient had a history of unilateral hearing loss and presented to her previous physician with a 3-day history of fever, right-sided abdominal pain, and diarrhea. Cefotaxime antimicrobial chemotherapy was initiated as an empiric therapy targeting E. coli, the most frequent cause of community-onset pyelonephritis. Vancomycin (VCM) was started for acute focal bacterial nephritis caused by methicillin-resistant S. saprophyticus but was stopped due to allergy and replaced with DAP. After 13 days of treatment with DAP, the patient received 17 days of treatment with sulfamethoxazole-trimethoprim combination therapy. The patient experienced no adverse events and did not relapse. DAP is a relatively new anti-methicillin-resistant Staphylococcus aureus drug used to treat gram-positive cocci infections. It is primarily excreted by the kidneys, which may be desirable in treating urinary tract infections. For children who cannot receive VCM for any reason, DAP may be a viable alternative.

Acute focal bacterial nephritis (AFBN) refers to the bacterial infection of the renal parenchyma without abscess formation. Although AFBN has mainly been reported in pediatric patients, it may be underdiagnosed in adults as it resembles acute pyelonephritis in its clinical presentation. However, the symptoms suggesting acute abdomen is an important clue to diagnose AFBN, which requires additional imaging studies such as contrast-enhanced computed tomography (CECT). Here, we present the case of a 49-year-old female presenting to our emergency room with acute abdomen as well as acute kidney injury (AKI). CECT was performed to rule out critical etiologies of severe abdominal pain and the results revealed multifocal wedge-shaped shadows in the right kidney and diffuse enlargement of bilateral kidneys. We diagnosed the patient with AFBN and treated her through temporal hemodialysis (two sessions) and antibiotics for 23 days. Although AKI associated with AFBN has rarely been reported, her renal dysfunction and other symptoms were completely improved. In conclusion, clinicians should be aware of AFBN and be cautious to avoid the unnecessary invasive interventions.

BACKGROUND: Multisystem inflammatory syndrome in children (MIS-C) is a rarely seen severe complication of coronavirus disease-2019 (COVID-19). Although fever is one of the indispensable symptoms, other infections should be considered in the differential diagnosis during the pandemic.
METHODS: An 8-year-old and a 16-year-old female patient were admitted with fever, vomiting, headache. Both had fulfilled the criteria and were diagnosed with MIS-C. However, they both had remarkable persistent costovertebral angle tenderness, which was unexpected in MIS-C. In Case-1, urine analysis showed microscopic hematuria without pyuria, and urine culture showed no bacterial growth. Case-2 had microscopic hematuria and pyuria with Escherichia coli growth in urine culture. Contrast-enhanced computed tomography showed wedge-shaped hypodense multiple lesions in bilateral kidneys for Case-1, in the right kidney for Case-2. They diagnosed acute focal bacterial nephritis (AFBN).
CONCLUSIONS: The diagnostic criteria of MIS-C can overlap with the symptoms of other severe septic infections such as AFBN, which is a rare urinary tract infection, diagnosed by imaging of localized renal inflammatory mass-like or wedge-shaped lesion. A detailed anamnesis and careful physical examination may help differential diagnosis.