What is the management for a 2-month-old infant presenting with fever and a bulging anterior fontanelle?

Management of a 2-Month-Old Infant with Fever and Bulging Anterior Fontanelle

Immediate Action Required

This infant requires immediate lumbar puncture, blood culture, urine culture, and empiric intravenous antibiotics after cultures are obtained, as the combination of fever and bulging fontanelle in a 2-month-old raises concern for bacterial meningitis, though the actual incidence is low (0.3-0.4%). 1, 2

Critical Clinical Assessment

Appearance and Vital Signs

• Determine if the infant appears ill or well-appearing, as only 58% of infants with bacteremia or bacterial meningitis appear clinically ill 3, 4
• Document rectal temperature (fever defined as ≥38.0°C/100.4°F) 4
• Assess for lethargy, listlessness, respiratory distress, poor feeding, or seizures—these findings combined with bulging fontanelle significantly increase concern for bacterial meningitis 1, 5
• If the infant appears well, is active, feeding normally, and has no altered consciousness, the risk of bacterial meningitis drops substantially 2, 6

Key Caveat About Bulging Fontanelle

• Bulging fontanelle has very low sensitivity (10%) and specificity for bacterial meningitis—in one study of 304 febrile infants with bulging fontanelle, only 1 (0.3%) had bacterial meningitis 2
• Most febrile infants with bulging fontanelle have self-limiting viral illnesses, including COVID-19 7, 6
• However, at 2 months of age (within the 29-90 day window), guidelines recommend lumbar puncture regardless of appearance because there are no adequate predictors to safely exclude meningitis 3, 1

Diagnostic Workup

Mandatory Testing for This Age Group

• Lumbar puncture for cerebrospinal fluid analysis: cell count with differential, glucose, protein, Gram stain, and bacterial culture 3, 1
• Blood culture (71% of bacterial meningitis cases have positive blood cultures) 1
• Catheterized urine specimen for urinalysis and culture (E. coli causes 87.4% of UTIs and 10% of UTIs are associated with bacteremia in this age group) 3
• Complete blood count with differential 3

Additional Considerations

• Consider COVID-19 testing, as recent case reports describe well-appearing infants with fever, bulging fontanelle, and COVID-19 who had benign courses 7, 6
• Chest radiograph is not routinely indicated unless respiratory symptoms (cough, hypoxia, rales) are present 4

Empiric Antibiotic Therapy

Immediate Treatment After Cultures

Initiate ampicillin PLUS either gentamicin or cefotaxime immediately after obtaining cultures 5

• Ampicillin: covers Group B Streptococcus and Listeria monocytogenes 5
• Gentamicin or cefotaxime: covers E. coli and other gram-negative organisms 5
• E. coli accounts for 43.7% of bacterial meningitis cases in this age group, Group B Streptococcus is the second most common pathogen 3, 1, 5

Duration and Follow-up

• Repeat lumbar puncture at 48-72 hours after initiating therapy to document sterilization of CSF 5
• Continue antibiotics for 14-21 days for Group B Streptococcus or Listeria, and at least 21 days for gram-negative meningitis 5

Disposition

Hospital Admission Required

• All febrile infants aged 29-90 days with suspected bacterial meningitis require admission for intravenous antibiotics and close monitoring 3
• Admission is necessary even if the infant appears well, given the age and concerning physical finding 3

If Lumbar Puncture is Deferred (Controversial)

• This is NOT recommended at 2 months of age with a bulging fontanelle, but if clinical judgment leads to deferral in a truly well-appearing infant with negative screening labs and confirmed viral illness, then: 3
  • Withhold antibiotics unless another bacterial source is identified 3
  • Require either admission for observation or very close follow-up with return visit within 24 hours 3

Risk Stratification Factors

Higher Risk Features (Increase Concern for Meningitis)

• Temperature >38.4°C (101.1°F) with WBC >6,100/mL increases risk of CSF pleocytosis to 7.3% 3, 1
• Presentation during summer months (June-September) increases risk to 17.4% vs. 5.0% in non-summer months 3, 1
• Ill appearance, lethargy, or altered mental status 1, 5

Common Pitfalls to Avoid

• Do not rely on the absence of meningeal signs—stiff neck and bulging fontanelle occur in only a minority of neonates with bacterial meningitis 5
• Do not assume bulging fontanelle equals meningitis—it has poor predictive value, but at 2 months of age, you cannot safely exclude meningitis without lumbar puncture 2
• Do not delay antibiotics if lumbar puncture is traumatic or cannot be performed—obtain blood and urine cultures and start empiric therapy 5
• Do not use bag-collected urine specimens—they have unacceptably high false-positive rates; catheterization is required 8