Diagnostic Approach to Recurrent Fever

Initial Assessment and First-Line Investigations

• Evaluate the pattern of fever episodes, including timing, duration, associated symptoms, and response to previous treatments, to identify potential infectious causes, according to the American College of Critical Care Medicine 1
• Review the complete medication history, including antibiotics and inhalers previously used, to assess for potential drug fever, as recommended by the American College of Critical Care Medicine 1
• Document the exact temperature measurements during fever episodes and any associated symptoms, such as chills or sweats, to inform the diagnostic process, based on guidelines from the American College of Critical Care Medicine 1
• Assess for specific symptoms during fever episodes that might localize the source of infection, considering the patient's history of upper respiratory tract infection and allergic bronchitis, as suggested by the American Thoracic Society 2
• Complete blood count with differential should be performed to evaluate for leukocytosis, leukopenia, or other hematologic abnormalities, as recommended by the American College of Critical Care Medicine 1
• Comprehensive metabolic panel is necessary to assess liver and kidney function, according to the American College of Critical Care Medicine 1
• Blood cultures, at least two sets, should be obtained during or just before fever episodes to identify potential bacterial causes, as advised by the Infectious Diseases Society of America 3, 4
• Urinalysis and urine culture are essential to rule out occult urinary tract infection, based on guidelines from the American College of Critical Care Medicine 1
• Chest radiography should be performed to evaluate for persistent pneumonia, bronchiectasis, or other pulmonary pathology, as recommended by the American Thoracic Society 1, 2
• C-reactive protein and erythrocyte sedimentation rate tests are necessary to assess the degree of inflammation, according to the American College of Critical Care Medicine 1

Second-Line Investigations and Management

• If respiratory symptoms persist, a high-resolution CT scan of the chest should be considered to evaluate for bronchiectasis, interstitial lung disease, or occult infection, as suggested by the Infectious Diseases Society of America 4 and the American Thoracic Society 2
• For persistent fever without an obvious source, a CT scan of sinuses should be performed to evaluate for chronic sinusitis, based on guidelines from the Infectious Diseases Society of America 4
• Abdominal ultrasound or CT is necessary to evaluate for occult intra-abdominal infection, abscess, or malignancy, as recommended by the Infectious Diseases Society of America 3, 4
• Echocardiogram should be considered to rule out endocarditis if blood cultures are positive or there are cardiac murmurs, according to the American College of Critical Care Medicine 1
• The American College of Clinical Microbiology recommends evaluating for inadequate treatment of the initial respiratory infection by reviewing the antibiotic choice, dosage, and duration for the initial upper respiratory tract infection 5, 6
• Consideration of resistant organisms is crucial if the patient received multiple courses of antibiotics, as advised by the American College of Clinical Microbiology 5, 6
• Assessment for post-viral bronchial hyperreactivity that may be misdiagnosed as allergic bronchitis is necessary, based on guidelines from the American Academy of Allergy, Asthma, and Immunology 7, 8

Management Algorithm

• The initial visit should include a complete history, physical examination, and first-line laboratory tests, as recommended by the American Thoracic Society 2
• If a clear source is identified, treatment should be initiated accordingly, based on guidelines from the Infectious Diseases Society of America 4
• If no source is identified, second-line investigations should be pursued, as suggested by the American College of Critical Care Medicine 1
• Reassessment of response to any initiated treatments should occur within 3-5 days, considering the patient's clinical presentation and laboratory results, according to the Infectious Diseases Society of America 3
• Empiric antibiotic discontinuation should be considered if drug fever is suspected, as recommended by the Infectious Diseases Society of America 4
• Further diagnostic workup, including CT scans and specialist consultation, may be necessary if fever persists, based on guidelines from the Infectious Diseases Society of America 4 and the American College of Critical Care Medicine 1