Differential Diagnosis

The patient's presentation with fever, headache, nonproductive cough, nausea, vomiting, and lack of energy, along with the development of shortness of breath and a right lower lobe infiltrate on chest x-ray, suggests a respiratory infection. The following differential diagnoses are considered:

• Single Most Likely Diagnosis
  • Mycoplasma pneumoniae infection: This is a common cause of community-acquired pneumonia in children and young adults, particularly during the winter months. The patient's symptoms, such as fever, headache, and nonproductive cough, are consistent with this diagnosis. The fact that his mother also became ill with similar symptoms suggests a contagious etiology, which is consistent with Mycoplasma pneumoniae.
• Other Likely Diagnoses
  • Influenza: The patient's symptoms, such as fever, headache, myalgias, and nonproductive cough, are consistent with influenza, particularly during the winter months.
  • Respiratory syncytial virus (RSV) infection: Although more common in younger children, RSV can cause pneumonia in older children, especially those with underlying medical conditions.
  • Adenovirus infection: Adenovirus can cause a range of respiratory symptoms, including pneumonia, and is a common cause of infection in children.
• Do Not Miss Diagnoses
  • Pneumococcal pneumonia: Although the patient's symptoms are not typical of pneumococcal pneumonia, it is a potentially life-threatening condition that requires prompt treatment. The presence of a right lower lobe infiltrate on chest x-ray increases the suspicion for this diagnosis.
  • Influenza A (H1N1) pneumonia: This diagnosis is particularly important to consider during influenza season, as it can be severe and require specific treatment.
  • Pertussis: Although the patient's symptoms are not typical of pertussis, it is a contagious and potentially severe condition that requires prompt treatment.
• Rare Diagnoses
  • Legionnaires' disease: This is a rare cause of community-acquired pneumonia, but it can be severe and requires specific treatment.
  • Psittacosis: This is a rare cause of pneumonia caused by Chlamydophila psittaci, which is typically associated with exposure to birds.
  • Q fever: This is a rare cause of pneumonia caused by Coxiella burnetii, which is typically associated with exposure to animals or contaminated environments.