Respiratory Syncytial Virus (RSV) Antigen
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Acute respiratory disease caused by respiratory syncytial virus (RSV) is a particularly debilitating infection in infants and young children. The usual manifestations are upper respiratory disease with rhinitis and fever, which often progress to bronchiolitis, pneumonia, or both in primary infections, especially in infants <6 months of age. Hospitalization is considered early in the course of the disease in infants at risk for severe RSV infections, such as infants with congenital heart disease or bronchopulmonary dysplasia.
The conventional method for laboratory diagnosis of RSV infection has been the inoculation of cell cultures with detection of characteristic cytopathic effects after several days incubation (range, 3-14 days). The efficiency of this method is hampered by the lability of the virus in transit to the laboratory and the lack of sensitivity of cell lines to produce infection with the virus.
Direct testing for RSV antigen is rapid, sensitive, and specific when compared to cell culture methods. With the availability of ribavirin therapy for serious RSV infections, rapid diagnostic tests for this virus have become increasingly important.
Rapid identification of patients with respiratory syncytial virus (RSV) infections
Detection of RSV antigen from nasopharyngeal specimens
Compared to tissue culture, the sensitivity of the respiratory syncytial virus (RSV) antigen assay is 93% to 97%, and the specificity is 90% to 97%.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
The etiology of respiratory infection caused by microorganisms other than respiratory syncytial virus (RSV) will not be established with this test.
This assay is capable of detecting both viable and non-viable RSV particles.
Test performance depends on antigen load and may not correlate with tissue culture performed on the same specimen.
It has been previously established that fresh specimens are preferable to frozen for RSV testing. Suboptimal test performance may result with the latter. Fresh specimens should be transported to the laboratory as rapidly as possible. Nasal washes may be stored refrigerated (2-8 degrees C) for up to 24 hours, eluted nasopharyngeal swabs for up to 48 hours refrigerated, or both can be frozen at -20 degrees C for up to 1 week prior to processing.
Inadequate specimen collection, improper specimen handling or transport, or low levels of virus shedding, may yield a false-negative result. Accordingly, a negative test result does not eliminate the possibility of an RSV infection. Patient diagnosis should always include laboratory test results in concert with all other clinical information available.
The rate of positivity observed will vary, depending on the method of specimen collection, handling and transport system employed, time of year, age of the patient, geographic location, and most importantly, local disease prevalence.
Throat swabs are not acceptable.
Excessively mucoid specimens may fail to be absorbed into the test membrane or may yield uninterpretable results.
Specimens containing blood have been found to yield uninterpretable or false-positive results.
Assay performance characteristics not established for use on specimens from patients > or =5 years old. Interpret results in conjunction with clinical findings.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Falsey AR, Walsh EE: Respiratory syncytial virus infection in adults. Clin Microbiol Rev 2000;13:371-384
2. Staat MA: Respiratory syncytial virus infections in children. Semin Respir Infect 2002;17:15-20
3. Swenson PD, Kaplan MH: Rapid detection of respiratory syncytial virus in nasopharyngeal aspirates by a commercial enzyme immunoassay. J Clin Microbiol 1986;23:485-488