Differential Diagnoses for a 7-Month-Old with Vomiting, Fever, and Poor Oral Intake
The three most critical differential diagnoses to consider are: (1) viral gastroenteritis, (2) urinary tract infection, and (3) bacterial meningitis or sepsis.
Most Likely Diagnosis: Viral Gastroenteritis
- Viral gastroenteritis is the most probable diagnosis in a 7-month-old presenting with vomiting and fever, as watery diarrhea and vomiting in a child less than 2 years of age most likely represent viral gastroenteritis 1.
- This age group is particularly susceptible, with rotavirus infection being a common culprit requiring hospitalization in 10% of cases 2.
- The combination of vomiting, fever, and poor oral intake fits the classic presentation of acute gastroenteritis, which accounts for 1.5 million office visits annually in U.S. children 3.
Critical Life-Threatening Differentials to Exclude
Bacterial Meningitis and Sepsis
- Fever, vomiting, and poor oral intake can be presenting symptoms of meningitis, bacterial sepsis, or other serious bacterial infections that require immediate recognition 1.
- Look specifically for: toxic appearance, altered mental status or lethargy, inconsolable crying or excessive irritability, and signs of poor perfusion 4, 5.
- A 7-month-old with fever and vomiting warrants careful assessment to rule out central nervous system infection, as these symptoms are nonspecific and can represent serious illness 1.
Urinary Tract Infection
- UTI is a common non-gastrointestinal cause of fever and vomiting in infants and must be considered in the differential 1.
- This is particularly important because UTI can present with minimal localizing symptoms at this age.
- Fever with vomiting in an infant should prompt consideration of urinary tract pathology 1.
Other Important Differentials Based on Red Flags
Surgical Emergencies (If Bilious Vomiting Present)
- If vomiting is bilious (green), immediately consider malrotation with midgut volvulus, which is a surgical emergency that can cause complete intestinal necrosis within hours 4, 6.
- Intussusception should be considered if there is abdominal pain, "currant jelly" stools, or progression to bilious vomiting 4.
- At 7 months, intussusception is within the classic age range and presents with the triad of crampy abdominal pain, bloody stools, and vomiting 4.
Other Serious Infections
- Pneumonia and otitis media can present with fever, vomiting, and poor oral intake in this age group 1.
- These respiratory and ear infections are common mimics of gastroenteritis in infants.
Clinical Assessment Priorities
Immediate Red Flag Assessment
- Determine if vomiting is bilious or non-bilious, as bilious vomiting requires immediate surgical evaluation regardless of other findings 4, 7, 6.
- Assess for hematemesis or hematochezia, which indicate GI bleeding requiring urgent assessment 4.
- Evaluate for signs of severe systemic illness: toxic appearance, lethargy, altered consciousness, or seizures 4, 5.
Hydration Status Evaluation
- Assess degree of dehydration using clinical signs: mild (3-5% deficit) shows increased thirst and slightly dry mucous membranes; moderate (6-9% deficit) shows loss of skin turgor and dry mucous membranes; severe (≥10% deficit) shows lethargy, prolonged skin tenting >2 seconds, cool extremities, and decreased capillary refill 1.
- The most reliable predictors of dehydration are abnormal capillary refill, abnormal skin turgor, and abnormal respiratory pattern 8.
- Infants are at higher risk for dehydration due to higher body surface-to-weight ratio and higher metabolic rate 1.
Physical Examination Specifics
- Palpate for abdominal tenderness or distension, which suggests surgical pathology 4.
- Check for hepatosplenomegaly, which may suggest metabolic disease or systemic infection 4.
- Assess fontanelle (bulging suggests increased intracranial pressure; sunken suggests dehydration) 1.
- Evaluate for signs of meningeal irritation if fever is prominent 5.
Common Pitfalls to Avoid
- Do not assume viral gastroenteritis without excluding serious bacterial infections, particularly meningitis, sepsis, UTI, and pneumonia in a febrile infant 1.
- Normal abdominal radiographs do not exclude malrotation or volvulus—if bilious vomiting is present, proceed directly to upper GI contrast study 4, 6.
- Do not rely solely on presence or absence of diarrhea; vomiting alone can be the presenting symptom of multiple serious conditions including metabolic disorders and increased intracranial pressure 1.
- Clinical suspicion based on presentation should drive evaluation, not just the most common diagnosis 5.