Fever without a source (FWS) in pediatric patients represents one of the most common and challenging presentations in clinical practice. This condition refers to a documented fever—typically defined as a rectal temperature ≥38.0°C (100.4°F)—in children where no clear source of infection is identified after a thorough history and physical examination. Accurate and timely evaluation is essential, as the underlying cause may range from benign viral illness to life-threatening bacterial infections.
Defining Pediatric Fever Without a Source (FWS)
FWS is differentiated based on age groups, due to varying risks and immune responses:
- Neonates (0–28 days)
- Infants (29–90 days)
- Young children (3 months–36 months)
- Older children (>3 years)
Each group requires a distinct diagnostic and management approach due to differences in immunity and risk of serious bacterial infections (SBIs).
Etiology: Common and Serious Causes of Pediatric Fever Without a Source
The majority of pediatric FWS cases are caused by self-limiting viral infections. However, bacterial pathogens remain a critical concern, especially in younger infants.
Viral Causes:
- Enteroviruses
- Adenovirus
- Influenza, RSV
- Human herpesvirus 6 (HHV-6)
- Parainfluenza, Rhinovirus
Bacterial Causes:
- Escherichia coli (most common in neonates)
- Group B Streptococcus
- Streptococcus pneumoniae
- Haemophilus influenzae type b (in unvaccinated)
- Neisseria meningitidis
- Salmonella species
Clinical Assessment Based on Age Group
Neonates (0–28 Days)
This age group carries the highest risk of invasive bacterial infection (IBI), including sepsis, meningitis, and urinary tract infections (UTIs). All neonates with FWS require:
- Hospital admission
- Full sepsis workup including CBC, blood cultures, urinalysis with culture, and lumbar puncture
- Empiric IV antibiotics (ampicillin + gentamicin or cefotaxime)
Infants (29–90 Days)
Evaluation depends on clinical appearance and laboratory findings:
- Low-risk criteria (e.g., Rochester, Boston, Philadelphia criteria) may permit outpatient management
- Lab tests: CBC, procalcitonin, CRP, urinalysis, possibly lumbar puncture
- UTI is the most common SBI in this group
Children (3–36 Months)
This group benefits from improved immune defenses and routine vaccination (Hib, PCV). Assessment focuses on:
- Urinalysis and culture (especially in girls <2 years and uncircumcised boys <12 months)
- Chest radiograph if respiratory signs present
- Blood culture only if ill-appearing or incomplete vaccination history
Children >36 Months
In well-appearing, immunized children, FWS is often viral. Targeted investigations based on clinical presentation are appropriate.
Diagnostic Workup: Investigations by Clinical Scenario
Laboratory Testing:
| Test | Utility |
|---|---|
| CBC with differential | Detects leukocytosis or neutrophilia indicative of bacterial infection |
| CRP and Procalcitonin | Helpful biomarkers to distinguish viral from bacterial causes |
| Blood cultures | Essential in febrile infants, especially <3 months |
| Urinalysis & culture | Most important in diagnosing occult UTI |
| Lumbar puncture | Indicated in neonates or if meningitis suspected |
| Chest X-ray | If respiratory symptoms or leukocytosis >20,000/mm³ |
Advanced Testing:
- PCR panels for viral pathogens
- COVID-19 and Influenza swabs depending on seasonality
- Malaria smears, typhoid tests, tuberculosis screen in endemic areas or travel history
Red Flags Requiring Immediate Intervention
- Lethargy or irritability
- Poor feeding or dehydration
- Respiratory distress
- Petechial or purpuric rash
- Seizures or bulging fontanelle
- Hypotonia or cyanosis
These features strongly suggest IBI and warrant hospital admission and empiric antibiotics.
Management Strategies
Empiric Antibiotic Therapy:
| Age Group | Recommended Antibiotics |
|---|---|
| 0–28 days | Ampicillin + Gentamicin or Cefotaxime |
| 29–90 days | Ceftriaxone ± Ampicillin |
| >3 months (if needed) | Ceftriaxone or Amoxicillin (based on source) |
Note: Antibiotic stewardship is crucial—therapy should be guided by culture results and local resistance patterns.
Outpatient Follow-Up:
For low-risk, well-appearing infants and older children:
- Ensure reliable caregivers and return precautions
- Re-evaluation within 24–48 hours
- Phone follow-up if feasible
Role of Vaccinations in Reducing FWS
Routine immunizations, especially Haemophilus influenzae type b (Hib) and Pneumococcal conjugate vaccine (PCV13), have significantly reduced cases of occult bacteremia and serious infections in children.
Children who are under-immunized or not up-to-date remain at greater risk and should be managed more cautiously.
Special Considerations
Pediatric Patients with Underlying Conditions:
Children with chronic diseases (e.g., sickle cell anemia, immunodeficiencies, malignancy) require individualized and often aggressive evaluation due to their heightened vulnerability to severe infections.
Travel and Epidemiological History:
- Recent travel may expose children to malaria, dengue, typhoid, or rickettsial infections
- Consider zoonotic exposures, insect bites, or unpasteurized dairy consumption
Pediatric fever without a source demands a systematic, age-based approach to balance early identification of serious infections with appropriate resource utilization. By combining clinical judgment with evidence-based protocols, we can minimize risks, ensure timely intervention, and improve outcomes for young patients.
