Synonym

• Nasal Swab RSV
• Respiratory syncytial virus nasal swab

Tubes

• Test tube with screw cap/vial provided by the laboratory
• Sterile cotton or Dacron swab
• Nasal swab specimens are collected from both nostrils
• A sterile swab is gently inserted 2-3 cm into the nostril and rotated 2–3 times against thesurface of the nasal cavity
• The swab is taken out and put into a vial containing 2.5 mL of viral transport medium (5% tryptose phosphate broth, 0.5% bovine serum albumin, and antibiotics in phosphate-buffered saline provided by the lab)

Additional information

• Samples should be collected within the first 3-4 days of onset of illness
• Before collecting the sample, inform the patient/parent that the test will not be painful, but it may tickle the nose and cause the eyes to tear
• Send sample to lab immediately
• If delayed, specimen should be stored at 4°C for the first 3-5 hours and at -70°C thereafter

Info

• RSV nasal swab test is performed to detect the presence of human respiratory syncytial viral RNA, antigens, or antibodies, from the nasal swab specimen/ nasal cavity
• RSV is a negative sense, single stranded, enveloped RNA virus of paramyxoviridae family and pneumovirinae subfamily
• RSV is the major causative factor of lower respiratory tract infections, especially bronchiolitis and pneumonia in infants and young children
• Various diagnostic tests are available to detect RSV, and the sensitivity and specificity of these tests may vary depending on the laboratory that performs the test, the type of test used, and the type of specimen tested. The diagnostic tests include:
• Indirect immunofluorescence
• Polymerase chain reaction (PCR)
• Rapid direct fluorescent antibody assays
• Serology (Enzyme immunoassays)
• Viral culture

Clinical

• The clinical utility of RSV nasal swab test includes the following:
• To diagnose RSV infection in patients with symptoms consistent with RSV infection
• To detect the presence of respiratory syncytial virus in respiratory tract infections, especially in susceptible persons such as:
• Infants
• Young children
• Elderly persons
• Immunocompromised persons
• Rapid diagnosis for timely treatment and isolation of patients
• To document and track the spread of RSV in community outbreaks and epidemics
• To detect RSV and prevent exacerbations of underlying diseases such as asthma and chronic obstructive pulmonary disease
• In the differential diagnosis of respiratory tract infections with similar clinical symptoms such as:
• Asthma
• Bronchiolitis
• Bronchitis (acute and chronic)
• Croup
• Influenza
• Neonatal sepsis
• Parainfluenza
• Pneumonia
• Viral upper or lower respiratory tract infections
• Laboratory studies are typically not indicated in infants or children with symptoms of respiratory tract infection who do not appear ill
• RSV infection occurs worldwide and affects most children at least once by 2 years of age. It occurs as epidemics during the late fall, winter, or early spring months and during annual community outbreaks in temperate climates
• The primary mode of transmission is by contact with aerosolized droplets from the nose or throat of an infected person
• RSV has an incubation period of 4-6 days
• The clinical severity ranges from that of a mild cold to serious lower respiratory tract symptoms that may require ventilatory support (especially in infants)
• Viral shedding may persist for several weeks even after symptoms subside
• The onset of infection is with upper respiratory tract (URT) symptoms and progresses over several days to the development of diffuse small airway disease in 25-40% of infants and young children, of which 1-2% require hospitalization. Most children recover from illness in 8-15 days
• RSV infection may clinically present as:
• Low grade fever
• Rhinorrhea (runny nose)
• Cough
• Tachypnea
• Cyanosis
• Retractions
• Wheezing
• Rales
• Irritability, listlessness, and poor feeding in infants
• Ear infection
• Repeated infections with RSV can occur throughout life with mild to severe cold like symptoms
• Factors resulting in severe lower respiratory tract disease with significant morbidity and mortality in susceptible individuals include:
• Premature infants in the first year of life
• Infants less than 8 weeks of age
• Infants with congenital heart disease and chronic lung conditions, including bronchopulmonary dysplasia and cystic fibrosis
• Immunocompromised individuals (AIDS, chemotherapy, or other immunosuppression)
• Lower socioeconomic status and crowded living conditions
• Exposure to environmental pollutants such as cigarette smoke
• Young children in day care centers
• Infants who were not breastfed
• Children with metabolic and neuromuscular disorders
• Multiple birth infants
• The elderly

Additional information

• Nosocomial spread of RSV infection can be reduced by cohorting and by contact isolation
• Laboratory diagnostic methods for the detection of respiratory syncytial virus infection include:
• Rapid direct and indirect fluorescent antibody assays: Quality of the specimen i.e., the presence of epithelial cells can be assessed with these tests. The sensitivity (73-95%)and specificity (69-99%) of these tests is better in the following conditions:
  • Early phase of the infection
  • Severe infections
  • Infants <6 months
  
  In adults, the sensitivity and specificity of these tests are lower due to decreased amount of virus in the specimen
• Enzyme immunoassays (EIA): This test is used for quantitative detection of RSV antigen. The sensitivity of this test is 75-95% and specificity is 85-100%. The sensitivity of this test in immunocompromised adults also depends on the specimen collection site:
• Bronchoalveolar lavage (89%)
• Endotracheal aspirate (71%)
• Nasal swabs (15%)
• Viral culture (gold standard): The advantage of this test is that it can detect presence of other viruses along with RSV. However, this test is not rapidly reported and may not be available in all the laboratories. Confirmation is by observing cytopathic effects (CPE) and fluorescent detection. The sensitivity of this test ranges between 57% and 92%
• Polymerase chain reaction (PCR): The reverse transcriptase-PCR method has the advantage of increased sensitivity compared to viral culture, and also for antigen detection during acute RSV infections in adults

• Factors interfering with test results include:
• Improper technique of collection
• Failure to place specimen in transport medium
• Specimen not refrigerated or maintained at a cold temperature
• Failure to send specimen to lab immediately
• Sample that fails to contain moderate to large numbers of exfoliated respiratory tract columnar epithelial cells
• Related laboratory tests include:
• Blood culture
• Complete blood count
• Influenza testing
• Sputum microscopy and culture
• Chest radiograph

Nl Result

• Normal: Negative

High Result

A positive result is indicative of RSV infection.

It is important to note that a positive RSV result does not exclude other significant bacterial infection. It is not unusual to have both RSV infection and a concomitant bacterial infection.

References

• Centers for Disease Control: Respiratory syncytial virus. [Homepage on the Internet]. Last reviewed on January 21, 2005. Last accessed on January 24, 2007. Available at URL: http://www.cdc.gov/ncidod/dvrd/revb/respiratory/rsvfeat.htm
• Chavez-Bueno S et al. Respiratory syncytial virus bronchiolitis: current and future strategies for treatment and prophylaxis. Treat Respir Med. 2006;5(6):483-94.
• eMedicine from WebMD®. Respiratory Syncytial Virus Infection. [Homepage on the Internet] ©1996-2006. Last updated on March 24, 2006. Last accessed on January 24, 2007. Available at URL: http://www.emedicine.com/PED/topic2706.htm
• FalseyAR et al.Diagnosis of Respiratory Syncytial Virus Infection: Comparison of Reverse Transcription-PCR to Viral Culture and Serology in Adults with Respiratory Illness. J Clin Microbiol. 2002 March;40(3):817–820.
• Laboratory Corporation of America. Virus, Direct Detection DFA, Respiratory Syncytial Virus. [Homepage on the internet]©2003. Last updated on November 15, 2006. Last accessed on January 24, 2007. Available at URL: http://www.labcorp.com/datasets/labcorp/html/chapter/mono/mb026400.htm
• LabTestsOnline®. RSV. [Homepage on the Internet]© 2001-2006. Last reviewed on April 25, 2005. Last accessed on January 24, 2007. Available at URL: http://www.labtestsonline.org/understanding/analytes/rsv/glance.html
• Lazzaro T et al. Respiratory syncytial virus infection and recurrent wheeze/asthma in children under five years: An epidemiological survey. J Pediatr Child Health. 2007 Jan;43(1-2):29-33.
• Macfarlane P et al. RSV testing in bronchiolitis: which nasal sampling method is best? Arch Dis Child. 2005 Jun;90(6):634-5.
• UTMB Laboratory Survival Guide®. RESPIRATORY SYNCYTIAL VIRUS, DIRECT. [Homepage on the Internet]© 2006. Last reviewed on July 19, 2004. Last accessed on January 24, 2007. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/micro/RESPIRATORY%20SYNCYTIAL%20VIRUS%20DIRECT%20TEST.html