How should respiratory syncytial virus infection be diagnosed in infants, young children, older adults, or immunocompromised patients presenting with acute upper or lower respiratory tract symptoms?

How to Diagnose RSV Infection

Use nucleic acid amplification testing (NAAT/RT-PCR) on a nasopharyngeal swab as the primary diagnostic method for RSV infection in all patient populations—it is the most sensitive test available and should be your first-line approach. 1, 2

Optimal Diagnostic Testing Strategy

First-Line Testing Approach

• Collect a nasopharyngeal swab or nasal aspirate and send for NAAT/RT-PCR testing, which has become the diagnostic method of choice and gold standard for RSV detection 1, 2
• Several FDA-cleared NAAT platforms are available, including multiplex panels that can detect RSV alongside other respiratory viruses (e.g., FilmArray Respiratory Panel, ePlex Respiratory Pathogen Panel, Xpert Flu/RSV XC) 1
• NAAT is significantly more sensitive than older methods: compared to rapid antigen detection tests (64% sensitivity), direct fluorescent antibody (83% sensitivity), and viral culture (86% sensitivity) 3

Specimen Collection Priorities

For immunocompetent patients with upper respiratory symptoms:

• Nasopharyngeal swab or nasal aspirate is sufficient 1, 2
• Transport in sterile container or viral transport medium at room temperature within 2 hours 1

For immunocompromised patients or those with lower respiratory tract infection:

• Obtain lower respiratory specimens (BAL fluid or endotracheal aspirate) in addition to upper respiratory samples, as lower tract specimens are dramatically more sensitive (BAL: 88.9% vs. nasal wash: 15%) 1, 2
• In immunocompromised adults, upper respiratory testing alone misses a substantial proportion of RSV infections 1

When to Enhance Diagnostic Yield

Add multiple specimen types when RSV suspicion remains high despite negative initial testing:

• Adding sputum RT-PCR to nasopharyngeal swab increases detection by 52% 3
• Adding oropharyngeal swab RT-PCR increases detection by 28% 3
• Adding paired acute and convalescent serology (4-fold rise in antibody titer) increases detection by 44%, though this is retrospective and not useful for acute management 3, 4

Alternative Testing Methods (Use Only When NAAT Unavailable)

Rapid Antigen Detection Tests

• Avoid relying on rapid antigen tests in adults, as sensitivity is poor (40-80%) due to lower viral loads compared to children 2
• Sensitivity and specificity range from 80-95% in children but may be even lower in actual practice 1
• Never accept a negative rapid antigen test as definitive—confirm with NAAT if clinical suspicion remains high 2

Direct Fluorescent Antibody (DFA) Staining

• Can provide results within hours but has reduced sensitivity (83%) compared to NAAT 3
• May be acceptable for rapid screening when NAAT is unavailable 1

Viral Culture

• Time-consuming with cytopathic effect potentially not observed for up to 2 weeks 1
• Has been largely replaced by molecular methods in clinical practice 1
• Sensitivity of 86% makes it inferior to NAAT 3

What NOT to Do

Do not use serology for acute diagnosis:

• RSV seroprevalence is high in the general population, and IgG antibodies indicate past exposure, not acute infection 1, 2
• Serology is only useful for epidemiological studies, not clinical diagnosis 2

Do not rely on clinical features alone:

• RSV symptoms (cough, nasal congestion, wheezing, low-grade fever) overlap significantly with other respiratory viruses 2, 5
• Laboratory confirmation is essential as clinical characteristics are indistinguishable from other viral respiratory infections 1, 5

High-Risk Populations Requiring Testing

Prioritize testing in these groups during RSV season (typically December-March):

• Infants and young children, especially those under 1 year or premature 5
• Elderly adults ≥65 years, particularly ≥75 years 5
• Patients with chronic cardiac or pulmonary disease 1, 5
• Immunocompromised individuals (including transplant recipients) 1, 5
• Residents of long-term care facilities 2

Critical Pitfalls to Avoid

• Never use upper respiratory specimens alone in critically ill or immunocompromised patients—always obtain lower respiratory specimens for higher sensitivity 1, 2
• Do not assume multiplex panels detect all targets with equal sensitivity—some panels have decreased sensitivity for RSV compared to singleplex NAAT 1
• Do not delay testing waiting for symptom progression—collect specimens in the early phase of disease for optimal viral detection 6
• Do not skip infection control measures while awaiting results—implement contact isolation precautions when RSV is suspected based on clinical presentation and epidemiology 1, 5