Golden Tips for Diagnosing Infections in Children
Age-Specific Pathogen Prediction
Age is one of the most powerful predictors of likely pathogens in pediatric infections, and should guide your initial diagnostic approach. 1
- Viruses predominate in younger children (under 3 years), accounting for 14–35% of community-acquired pneumonia cases as sole pathogens 1
- In older children with bacterial pneumonia, Chlamydia is the most common bacterial cause 1
- Streptococcus pneumoniae remains the most common bacterial pathogen overall across all pediatric age groups 1
- Mixed viral-bacterial infections occur in 8–40% of cases, so don't stop looking after finding one pathogen 1
Clinical Assessment Thresholds
For children under 3 years, bacterial pneumonia should be suspected when fever exceeds 38.5°C combined with chest recession and respiratory rate >50/min. 1
- In older children, a history of difficulty breathing is more diagnostically useful than physical examination signs alone 1
- The presence of wheeze in preschool children makes primary bacterial pneumonia unlikely 1
- Oxygen saturation <92% indicates severe disease requiring immediate hospitalization and oxygen therapy 1
Strategic Use of Investigations
What NOT to Order Routinely
Do not perform chest radiography routinely in children with mild, uncomplicated acute lower respiratory tract infections. 1
Do not measure acute phase reactants (CRP, ESR) routinely—they cannot distinguish bacterial from viral infections in children. 1
- CRP is <10 in 55% of influenza cases and <20 in 72% 1
- White blood cell counts and ESR show no significant difference between bacterial and viral pneumonia 1
- These tests generate false reassurance or unnecessary concern without changing management 1
What TO Order Strategically
Pulse oximetry should be performed in every child admitted to hospital with suspected infection. 1
Blood cultures should be obtained in all children suspected of having bacterial pneumonia or serious bacterial infection. 1
- For infants under 18 months, send nasopharyngeal aspirates for viral antigen detection (immunofluorescence) with or without viral culture 1
- Save acute serum samples and obtain convalescent samples when no microbiological diagnosis is reached acutely 1
- When significant pleural fluid is present, aspirate it for microscopy, culture, and bacterial antigen detection 1
Microbiological Yield Expectations
Accept that in 20–60% of pediatric infection cases, no pathogen will be identified despite appropriate testing. 1
This reality should not delay treatment when clinical suspicion is high. The absence of a positive culture does not exclude serious bacterial infection, especially if antibiotics were given before cultures were obtained 1.
Ultrasound as a Diagnostic Game-Changer
Ultrasound must be used to confirm pleural fluid collections—it is far superior to chest radiography alone. 1, 2, 3
- Ultrasound can detect fluid when chest X-ray shows only subtle costophrenic angle blunting 1, 3
- It differentiates free from loculated fluid and estimates fluid echogenicity 1
- Ultrasound should guide all thoracocentesis or drain placements 1
- In children with abdominal masses, ultrasound simultaneously assesses both the mass and any pleural complications 2
Red Flags Requiring Immediate Escalation
Admit infants to hospital if they have any of the following: 1
- Oxygen saturation <92% or cyanosis
- Respiratory rate >70 breaths/min
- Difficulty breathing, grunting, or intermittent apnea
- Not feeding
- Family unable to provide appropriate observation
Admit older children to hospital if they have: 1
- Oxygen saturation <92% or cyanosis
- Respiratory rate >50 breaths/min
- Difficulty breathing or grunting
- Signs of dehydration
- Family unable to provide appropriate observation
Infective Endocarditis: High-Suspicion Scenarios
Draw blood cultures for any child with unexplained fever plus a pathological heart murmur, history of heart disease, or previous endocarditis. 1
- Obtain 3 blood cultures by separate venipunctures on day 1; if no growth by day 2, obtain 2–3 more 1
- In acutely ill, unstable children, obtain 3 blood cultures over 1–2 hours and start empirical antibiotics immediately 1
- Viridans group streptococci and Staphylococcus aureus are the most common pathogens in pediatric endocarditis 1
Common Pitfalls to Avoid
Do not attribute findings to "just a viral infection" without excluding serious bacterial infection first, especially in children with underlying chronic conditions 4, 5
- Many pediatric bacterial infections present without elevated inflammatory markers 4
- Children with chronic neurologic disorders, prematurity, genetic syndromes, or obesity are at higher risk for severe infections 5, 6
Do not delay re-evaluation if a child remains febrile or unwell 48 hours after starting appropriate antibiotics. 1
- Repeat clinical examination and chest radiography to assess for complications 1
- Consider ultrasound to detect developing pleural effusion or other complications 1
Do not rely solely on automated differential counts—manual review by an experienced technician is mandatory when infection is suspected, particularly if leukemia or other hematologic conditions are in the differential 4
Avoid nasogastric tubes in severely ill infants with small nasal passages, as they may compromise breathing 1
Follow-Up Imaging Guidance
Perform follow-up chest radiography only after lobar collapse, apparent round pneumonia, or continuing symptoms—not routinely 1
- Most pediatric pneumonias resolve radiographically by 6 months without need for repeat imaging 1
- Unnecessary follow-up X-rays expose children to radiation without changing management 1
Special Considerations for High-Risk Groups
Children with medical complexity or chronic conditions (type 1 diabetes, cardiac anomalies, neurodevelopmental disorders, prematurity) require closer observation and lower thresholds for investigation. 5, 6, 7