What tests should be considered for patients presenting with Upper Respiratory Tract Infections (URTI)?

Testing for Upper Respiratory Tract Infections (URTI)

For uncomplicated URTI in immunocompetent patients, routine diagnostic testing is generally not recommended, as most cases are viral and self-limiting. Testing should be reserved for specific clinical scenarios where results will change management or infection control measures.

When to Consider Testing

Clinical Scenarios Warranting Testing

• Suspected influenza during flu season: Rapid nucleic acid amplification tests (NAATs) or rapid antigen tests can guide antiviral therapy and infection control, though evidence shows limited impact on antibiotic reduction 1
• Severe symptoms or high-risk patients: Testing may be appropriate in immunocompromised hosts, elderly patients, or those with significant comorbidities 2
• Suspected bacterial complications: When symptoms persist >10 days without improvement or worsen after initial improvement (double worsening), suggesting progression to acute bacterial rhinosinusitis 1
• Outbreak settings: Multiplex PCR testing can identify viral pathogens to implement appropriate infection control measures 1

Specific Testing Recommendations by Syndrome

For suspected acute bacterial rhinosinusitis (ABRS):

• Clinical diagnosis is preferred over routine testing 1
• Diagnosis requires purulent nasal discharge PLUS either nasal obstruction or facial pain-pressure-fullness 1
• Bacterial infection should be suspected when symptoms fail to improve after 10 days OR worsen within 10 days after initial improvement 1
• Routine nasal or nasopharyngeal cultures do NOT correlate with sinus cultures and are not recommended 1

For suspected streptococcal pharyngitis:

• Use Centor clinical criteria to guide testing decisions 3
• Rapid antigen detection tests or throat culture are appropriate when bacterial pharyngitis is suspected 3
• Penicillin V remains the treatment of choice for confirmed streptococcal infection 3

Specimen Collection

Optimal specimen types for viral detection:

• Upper respiratory tract: Nasopharyngeal swabs (preferably flocked), nasopharyngeal aspirates, or combined bilateral nasopharyngeal with throat swabs 1
• Lower respiratory tract involvement: Bronchoalveolar lavage is preferred over tracheal aspirates if pneumonia is suspected 1
• Pooled specimens (nasopharyngeal plus throat) often provide better yield than single-site sampling 1

Testing Modalities

Molecular Testing (NAATs)

• Advantages: Higher sensitivity than antigen tests or culture, results typically within 24 hours, can quantify viral loads 1
• Limitations: The 2024 European guidelines suggest AGAINST routine use of multiplex PCR for respiratory pathogens to initiate antibiotic treatment in emergency departments (weak recommendation, low certainty) 1
• May detect asymptomatic viral shedding, particularly in immunocompromised patients, requiring clinical correlation 1

Rapid Antigen Tests

• Advantages: Results in <15 minutes, reasonable specificity when positive 4
• Limitations: Lower sensitivity than NAATs, particularly for influenza 1
• The 2024 guidelines suggest AGAINST routine use of rapid antigen tests for influenza to reduce antibiotic initiation in emergency departments 1

Point-of-Care Testing

• Available for influenza, respiratory syncytial virus, Streptococcus pneumoniae, and Legionella 4
• Results in approximately 15 minutes with moderate sensitivity 4
• Should be confirmed with more accurate tests (cultures, PCR) when clinical decisions require certainty 4

Tests NOT Recommended for Routine URTI

• Urinary antigen testing for Streptococcus pneumoniae: Suggested AGAINST for routine use in LRTI patients in emergency departments 1
• Urinary antigen testing for Legionella pneumophila: Suggested AGAINST for routine use, EXCEPT in suspected legionellosis or outbreak settings 1
• Complete blood count: While elevated band count (>1500/mm³) has the highest likelihood ratio for bacterial infection, routine CBC is not specifically recommended for uncomplicated URTI 1
• Procalcitonin: Not recommended based on fever alone to guide antibiotic treatment (very low certainty evidence) 1

Special Populations

Immunocompromised patients:

• Lower threshold for testing given atypical presentations and unusual organisms 2
• Broader diagnostic testing including multiplex panels may be warranted 1
• Consider both upper and lower respiratory tract sampling if symptoms suggest progression 1

Nursing home residents:

• Testing should be considered during suspected outbreaks 1
• Clinical diagnosis remains challenging due to atypical presentations 1

Key Pitfalls to Avoid

• Do not culture nasopharyngeal specimens to diagnose bacterial sinusitis—they do not correlate with actual sinus pathogens 1
• Do not test asymptomatic patients unless required for infection control or pre-procedural screening in high-risk populations 1
• Do not rely solely on positive viral tests to withhold antibiotics if clinical features strongly suggest bacterial superinfection 1
• Recognize that viral detection does not exclude bacterial co-infection, particularly in immunocompromised hosts 1