Differential Diagnosis for a 6-Month-Old with Fever and Diarrhea

Single Most Likely Diagnosis

• Viral Gastroenteritis: This is the most common cause of fever and diarrhea in infants, often caused by rotavirus, norovirus, or adenovirus. The diagnosis is typically clinical, based on symptoms such as watery diarrhea, vomiting, and fever, in the absence of blood in the stool or severe abdominal pain. 1

Other Likely Diagnoses

• Bacterial Gastroenteritis: Caused by pathogens like Salmonella, Shigella, or Campylobacter. It can present similarly to viral gastroenteritis but may have blood in the stool and higher fever. 2
• Urinary Tract Infection (UTI): Although less common, UTIs can cause fever and nonspecific symptoms like irritability or poor feeding in infants, and sometimes diarrhea. 3
• Respiratory Infections: Such as pneumonia or bronchiolitis, which can cause fever and may lead to gastrointestinal symptoms due to dehydration or as a side effect of medications.

Do Not Miss Diagnoses

• Intussusception: A condition where a part of the intestine slides into an adjacent part, potentially causing bowel obstruction. It's a medical emergency and can present with intermittent abdominal pain, vomiting, and sometimes diarrhea or blood in the stool. 4
• Bacterial Meningitis: Although rare, it's critical to consider in infants with fever, especially if there are signs of severe illness, such as lethargy, seizures, or neck stiffness. 5
• Sepsis: Bacterial sepsis can cause fever, diarrhea, and vomiting, and is a life-threatening condition requiring immediate intervention. 6

Rare Diagnoses

• Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis are rare in infants but can cause chronic diarrhea, blood in the stool, and fever. 7
• Food Allergy or Intolerance: Can cause gastrointestinal symptoms, including diarrhea, but typically without fever unless there's an associated infection. 8
• Congenital or Acquired Immunodeficiency: Conditions that impair the immune system can lead to recurrent or severe infections, including those causing fever and diarrhea. 9

References: 1 Centers for Disease Control and Prevention. (2020). Viral Gastroenteritis. 2 American Academy of Pediatrics. (2018). Bacterial Gastroenteritis. 3 National Institute of Diabetes and Digestive and Kidney Diseases. (2020). Urinary Tract Infection in Children. 4 UpToDate. (2022). Intussusception in children: Clinical features and diagnosis. 5 World Health Organization. (2018). Bacterial meningitis. 6 Surviving Sepsis Campaign. (2020). Guidelines for Management of Sepsis. 7 Crohn's & Colitis Foundation. (2020). Inflammatory Bowel Disease in Children. 8 Food Allergy Research & Education. (2020). Food Allergies in Infants. 9 National Institute of Allergy and Infectious Diseases. (2020). Primary Immunodeficiency Diseases.