Respiratory syncytial virus (RSV) is one of the most common agents of upper and lower respiratory illnesses in infants and children worldwide. RSV typically occurs during the late fall, winter, and spring months and is generally self-limiting. Those infected may present with mild, coldlike symptoms that are clinically indistinguishable from those of other viral respiratory infections. However, RSV can also manifest as severe infections such as bronchiolitis and pneumonia and is a significant cause of morbidity and mortality in young children, older adults, and immunocompromised patients. The CDC estimates over 225,000 hospitalizations yearly among children and older adults combined. Routine laboratory testing for RSV is not recommended by the American Academy of Pediatrics because treatment is supportive only, and diagnosis does not change the management of disease for most patients ; however, laboratory testing may be warranted to confirm RSV infection in high-risk groups if the result will inform clinical decisions. For example, infants hospitalized with bronchiolitis who are receiving palivizumab should have testing to confirm whether RSV is the etiologic agent so that the treatment can be discontinued. RSV testing methodologies include nucleic acid amplification testing (NAAT), polymerase chain reaction (PCR) and rapid antigen detection tests (RADTs), and cell culture. The preferred testing methodology depends on the patient’s age and the clinical scenario.
Quick Answers for Clinicians
Although respiratory syncytial virus (RSV) is self-limited and uncomplicated in most healthy individuals, it can cause serious complications and result in increased morbidity and mortality in high-risk patients. Among symptomatic patients, RSV testing may be warranted in young children (especially infants younger than 6 months of age), in adults 65 years or older, and in those with underlying heart and lung diseases (eg, congestive heart failure, chronic obstructive pulmonary disease). Laboratory testing should only be performed when a diagnosis would alter patient management. For example, diagnosis is important for immunocompromised patients who may require early therapy and in infants receiving preventative palivizumab so that therapy can be stopped.
Laboratory testing is the only way to distinguish between SARS-CoV-2 and the flu. Importantly, laboratory testing is also the only way to determine cases of viral coinfection. Infection with one respiratory virus does not exclude the possibility of infection with another because patients may be infected with more than one virus at the same time. When SARS-CoV-2, influenza, and respiratory syncytial virus (RSV) are cocirculating (eg, during flu season), the National Institute of Health (NIH) recommends cotesting to determine proper medical management.
Respiratory syncytial virus (RSV) can be detected by rapid antigen detection tests (RADTs), direct fluorescent antibody (DFA) and polymerase chain reaction (PCR) testing, and culture. If RSV is the main concern, DFA testing or RADTs may be used, particularly in infants and children. If other respiratory viruses are also of concern, PCR panels are available that test for a spectrum of respiratory viruses, including RSV. PCR testing is generally more reliable in adults and is recommended for all hospitalized or immunocompromised patients. Viral culture, the traditional gold standard, is also available but not widely used due to the long turnaround time. Serologic testing is not used for primary RSV diagnosis and should be reserved for use in epidemiologic studies.
Next generation sequencing (NGS) is a rapidly evolving methodology that may be available at some laboratories. NGS tests might be considered when more traditional panel test results are negative and serious suspicion of infectious disease remains, and when identification of the underlying etiologic agent causing the illness may change or impact patient management. However, negative NGS test results do not definitively rule out viral, bacterial, or fungal infections. Targeted polymerase chain reaction (PCR)-based tests are generally more sensitive and preferred when specific pathogens are suspected.
Rapid antigen detection tests (RADTs) and direct fluorescent antibody (DFA) tests offer quick results and an acceptable sensitivity and specificity in infants and younger children. However, neither test type is useful in adults and older children. Polymerase chain reaction (PCR) testing is preferred in hospitalized patients and may be more useful in adults and older children; multiplex panels may also enable the detection of other respiratory viruses. However, PCR testing is more expensive than RADTs and DFA testing and has a longer turnaround time. Additionally, PCR testing may detect viral shedding in RNA even after the patient has cleared the infection.
Indications for Testing
RSV is usually diagnosed based on clinical presentation and patient history; however, the following populations warrant laboratory testing during RSV season if they present with severe respiratory illness:
- Young children (especially infants younger than 6 months of age)
- Adults 65 years or older
- Those with underlying heart and lung diseases (eg, congestive heart failure, chronic obstructive pulmonary disease)
Rapid Antigen Detection Tests
RADTs are popular for RSV testing due to their ease of use, quick turnaround time, and acceptable sensitivity and specificity in infants and young children. Some RADTs (eg, BinaxNOW RSV) can be used at the point of care in outpatient settings and require nasopharyngeal swabs or aspirates. However, false-negative results are possible, and clinicians may consider retesting by a more sensitive method (eg, PCR) if the result might influence patient management.
Direct Fluorescent Antibody
Direct fluorescent antibody (DFA) testing is a fairly reliable methodology for use in infants and young children; however, sensitivity in adults and older children is poor due to a lower rate of viral shedding compared to that in younger children. Because DFA is more cost-effective than molecular testing (eg, PCR), it is preferred for infants and young children. The sensitivity of DFA testing depends on an adequate specimen (nasopharyngeal swab or aspirate).
Polymerase Chain Reaction
Molecular testing (eg, PCR) can detect RSV as well as other respiratory viruses in nasopharyngeal swabs and aspirates with high sensitivity and specificity. Molecular testing is particularly useful in older children and adults and is preferred for hospitalized and immunocompromised patients. PCR is more sensitive than either antigen testing or viral culture. Because of its high sensitivity, it may detect RSV in a patient after the infection has resolved, so a positive result should be clinically correlated with the patient’s symptoms. Additionally, PCR is more expensive than DFA, and the turnaround time may be longer in certain laboratory settings.
Comparison of Testing Methodologies
ARUP Laboratory Tests
Direct Fluorescent Antibody Stain/Qualitative Polymerase Chain Reaction
Direct Fluorescent Antibody (DFA) Stain/Cell Culture
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