Indications for Testing
Although testing to identify a specific pathogen is not often indicated, it can be useful if the specific diagnosis will alter clinical management. Testing for respiratory viruses in general is indicated for immunocompromised patients presenting with severe LRTI. Influenza testing is indicated in at-risk patients with influenzalike symptoms, and respiratory syncytial virus (RSV) testing is indicated in infants and children presenting with severe respiratory infection. For more detailed indications, refer to the Influenza and Respiratory Syncytial Virus Consult topics.
Laboratory Testing
Diagnosis
Influenza Virus
Influenza (commonly referred to as the flu) is an acute viral infection that is highly transmissible, leading to outbreaks of varying severity during the winter in temperate regions. In most healthy individuals, the flu is self-limited and uncomplicated, but in high-risk patients, it can lead to serious complications. The Infectious Diseases Society of America (IDSA) recommends testing if the results will influence management decisions, such as whether to initiate antiviral therapy. If available, the near-point-of-care PCR test is preferred for diagnosis because of its rapid results and reasonably high sensitivity. For more information, refer to the Influenza Virus topic.
Respiratory Syncytial Virus
RSV is one of the most common agents of lower respiratory illnesses (including bronchiolitis and pneumonia) in infants and children worldwide. Laboratory testing is only indicated when diagnosis would change the course of patient management. For immunocompetent children, DFA testing and RADTs have adequate sensitivity. However, for adults and for all hospitalized and immunocompromised patients, the more sensitive PCR test is preferred. For more information, refer to the Respiratory Syncytial Virus topic.
Parainfluenza Virus
Parainfluenza virus is a common cause of croup (laryngotracheobronchitis), bronchiolitis, pneumonia, and upper respiratory tract infections. Clinical diagnosis is usually sufficient. If laboratory testing is necessary, consider concurrent DFA testing for other common respiratory viruses (eg, influenza, adenovirus, RSV). PCR testing is more expensive and less rapid than DFA testing, but unlike DFA, can detect the less common parainfluenza type 4.
Adenovirus
Adenoviruses usually cause mild, self-limiting respiratory illnesses, primarily in children. In immunocompetent patients, the diagnosis is typically based on clinical presentation. In immunocompromised individuals, adenovirus may cause severe, fatal disease, and laboratory testing is indicated. PCR testing is the preferred method for detecting adenovirus in this group.
Human Metapneumovirus
Human metapneumovirus (hMPV) is an agent of acute respiratory tract disease in people of all ages. The virus has been associated with bronchiolitis in infants and pneumonia, exacerbations of asthma and croup, and upper respiratory infections in children. Clinical presentation ranges from the common cold to pneumonia. When testing is indicated, DFA testing is generally preferred; PCR testing may be considered when DFA test results are negative but suspicion of infection is high. Because coinfection with other respiratory viruses is common, concurrent viral testing should be considered.
Laboratory Tests for Common Respiratory Viruses
| Etiologic Agent |
Laboratory Testing |
|---|
| Point-of-Care or Near-Point-of-Care Tests |
Singleplex/Multiplex PCR |
DFA |
Viral Culture |
| Influenza virus A and B |
xa |
x |
xb |
x |
| RSV |
xc |
x |
xb |
x |
| Parainfluenza virus |
|
x |
xd |
xd |
| Adenovirus |
|
x |
x |
x |
| hMPV |
|
x |
xb |
|
| Coronaviruses, rhinovirus, bocavirus |
|
x |
|
|
| aPCR and RADTs available
bRapid DFA
cRADT available
dFor types 1, 2, and 3; type 4 is only detectable using PCR
Sources: Ginocchio ; Henrickson ; Miller ; Loeffelholz
|
Comparison of Testing Methodologies
| Test Methodology |
Advantage(s) |
Disadvantage(s) |
|---|
| RADTs |
Often available as point-of-care test for influenza and RSV
Rapid turnaround time (<30 min)
Acceptable sensitivity and specificity in young children
|
Sensitivity may be low when compared to other methodologies, especially in adults
False-negative results are possible
|
| DFA testing |
Useful in infants and children due to high sensitivity and specificity in this patient population
Shorter turnaround time than viral culture or PCR
Less expensive than PCR or culture
|
May not be available for less common respiratory viruses, thus requiring NAAT
Sensitivity may be low when compared to other methodologies, especially in adults
Adequate specimen influences sensitivity of the assay
False-negative results are possible
Negative results may be confirmed with culture or NAAT if high suspicion remains
|
| PCR testing/NAAT |
Very high sensitivity and specificity
PCR panels can detect other respiratory viruses
Low likelihood of false-positive or false-negative result
Detects viruses in adults and older children, despite their lower viral shedding
|
Longer turnaround time than DFA
More expensive than DFA
May detect virus after the infection has been cleared
|
| Viral culture |
Traditional gold standard for diagnosis
May aid in detecting coinfections
Virus can be stored for diagnostic studies
High specificity
|
Long turnaround time
May require specific media for each virus
Lower sensitivity
|
| Serologic testing |
n/a |
Not useful for diagnosis |
| n/a, not applicable; NAAT, nucleic acid amplification testing
Sources: Chartrand ; Henrickson
|
