Laboratory diagnosis A variety of laboratory tests are available for the diagnosis of<unk>  infection. While the American Academy of Pediatrics (AAP) does not routinely recommend the use of lab testing to diagnosis<unk>  bronchiolitis (for which the treatment is largely supportive), confirmation of<unk>  infection may be warranted in high-risk groups if the result will guide clinical decisions. Common identification techniques include antigen testing, molecular testing, and viral culture. Antigen testing Antigen testing involves detection of<unk>  antigen fragments (or pieces of molecular viral structures), usually from an nasopharyngeal swab or aspirate. This can be accomplished either by viewing fluorescently labeled antigens under a microscope (direct fluorescence assay, or DFA) or using a commercially available rapid antigen detection test (RADT). Overall, antigen testing is highly sensitive in young children (80–90%) but substantially less reliable in older children and adults, who have less viral shedding. Antigen tests are also subject to higher false positive rates outside of the peak<unk>  season, such as in the summer months. In these scenarios, the use of either viral culture or nucleic acid amplification testing (NAAT) may aid in an accurate<unk>  diagnosis. * Rapid antigen detection tests (RADT) are commonly used as point-of-care testing due to their ease of use and quick turnaround time (as little as 10 minutes). These include both enzyme immunosorbent assays (EIA) and chromatographic immunoassays (CIA). * Direct fluorescence assay (DFA) allows for direct microscopic examination of virus-infected cells. The sensitivity of DFA testing depends on an adequate specimen. Molecular testing Molecular assays, such as nucleic acid amplification tests (NAATs), enable sensitive detection of very small amounts of virus in nasopharyngeal swabs and aspirates. NAAT assays such as polymerase chain reaction (PCR) detect virus-specific genetic material, rather than viral antigens. They have a sensitivity and specificity approaching 100%. However, they tend to be more expensive and require more complex equipment than other testing methods, making them less practical in resource limited areas. * Polymerase chain reaction (PCR) is type of NAAT which allows a very small sample of genetic material to be rapidly amplified into millions of copies for study. PCR is more sensitive than either antigen testing or viral culture. Therefore, it can be used to detect virus in those with lower viral shedding, such as older children and adults. It may also be used to detect the disease earlier in at risk-at individuals (such as hospitalized or immunocompromised patients), when the viral burden may still be too low to be identified by traditional techniques. Because of its sensitivity, PCR can also often detect asymptomatic carriers and may remain positive even days after an infection has clinically resolved. * Multi-pathogen panels are also available, which can detect the presence of multiple viral infections (including<unk>  in a single patient. Viral culture In traditional viral culture, a sample of the virus is introduced to different cell lines and allowed to replicate so it can be studied. Benefits of this technique include the ability to perform genetic characterization, strain typing, and antiviral susceptibility testing. However, it is limited by its prolonged turnaround time of 3–7 days, making it less common in patient care and more common in research settings. Serologic testing Serology (the measurement of virus-specific antibodies in the serum) is not frequently used in<unk>  diagnosis. The time required for the body to mount a significant serologic response (and demonstrate a significant rise in antibodies that can be detected in serum) is usually not useful in guiding patient care. Up to 30% of patients with documented<unk>  infection will have negative serology results. As such, this method is generally reserved for research and surveillance studies. Imaging findings X-ray of a child with<unk>  bronchiolitis showing the typical bilateral perihilar fullness Chest x-rays findings in children with<unk>  bronchiolitis are generally nonspecific and include perihilar markings, patchy hyperinflation, and atelectasis. However, the American Academy of Pediatrics (AAP) does not recommend routine imaging for children with presumed<unk>  bronchiolitis because it does not change clinical outcomes and is associated with increased antibiotic use. Chest x-ray is sometimes considered when the diagnosis of bronchiolitis is unclear or when there is an unexpected worsening. In adults with<unk>  infection, chest films are often normal or demonstrate nonspecific changes consistent with viral pneumonia, such as patchy bilateral infiltrates. Differential diagnosis The differential diagnosis for individuals presenting with signs and symptoms of upper and lower<unk>  tract infection includes other viral infections (such as rhinovirus, metapneumovirus, and influenza) and primary bacterial pneumonia. In children, inhaled foreign bodies and congenital conditions such as cystic fibrosis or asthma should also be considered.
Respiratory syncytial virus
Influenza A virus
Influenza B virus
Influenza D virus
Rhinovirus
Human parainfluenza viruses
Human coronavirus 229E
Cricket paralysis virus