Differential Diagnosis for Unvaccinated 4-year-old with Fever, Cough, Rhinorrhea, and Conjunctivitis

• Single Most Likely Diagnosis
  • Pertussis (Whooping Cough): Given the symptoms of fever, cough, rhinorrhea, and the patient being unvaccinated, pertussis is a highly likely diagnosis. The presence of conjunctivitis, although less common, can occur in the context of a severe respiratory infection.
• Other Likely Diagnoses
  • Influenza: This viral infection can cause fever, cough, and rhinorrhea. Conjunctivitis can sometimes be associated with influenza, especially in children.
  • Adenoviral infection: Adenoviruses can cause a range of symptoms including fever, cough, rhinorrhea, and conjunctivitis, making it a plausible diagnosis.
  • Respiratory Syncytial Virus (RSV) infection: Although more common in younger children, RSV can cause similar symptoms and should be considered, especially during peak RSV seasons.
• Do Not Miss Diagnoses
  • Measles: Given the unvaccinated status and the combination of fever, cough, rhinorrhea, and conjunctivitis, measles is a critical diagnosis not to miss due to its potential for severe complications and public health implications.
  • Meningitis: Although the symptoms do not directly point towards meningitis, in an unvaccinated child, the possibility of a bacterial infection such as Haemophilus influenzae type b (Hib) or Streptococcus pneumoniae should be considered, especially if there are signs of severe illness or if the child's condition worsens.
• Rare Diagnoses
  • Mycoplasma pneumoniae infection: This bacterium can cause atypical pneumonia, which might present with similar symptoms. It's more common in school-aged children but could be considered in a differential diagnosis.
  • Chlamydia trachomatis pneumonia: Although less common, this should be considered in the differential, especially if there's no clear response to initial treatments or if the clinical picture suggests a different pathogen.