Influenza Diagnosis
A variety of diagnostic tests are available for influenza virus detection, but there is no need to do testing for each influenza infection patient. The diagnostic tests are more beneficial in individual patients who are more likely to attain clinically possible results, which will help with the treatment decisions. When there is an outbreak of a respiratory illness in a closed facility such as long-term care centers, boarding schools, hospitals, cruise ships, or summer camps, then diagnostic testing for influenza can help determine the cause of the outbreak. Some of the useful tests for influenza diagnosis include serology, viral culture, reverse transcription-polymerase chain reaction (RT-PCR), rapid molecular assays, rapid antigen testing, and immunofluorescence assays. The specificity and sensitivity of each test for influenza might differ by the laboratory, which happens to perform the test, the time from the onset of illness to the collection of specimens, the type of test applied, and the specimen’s form use for testing.
For the collection of respiratory specimens to rapidly detect human influenza viruses or viral isolation, the use of nasal or throat swabs as specimens is not as effective as nasopharyngeal specimens. The nasopharyngeal specimens give more yield than any other specimen. As with every diagnostic testing, the doctors’ team must evaluate the test results in the contest of other epidemiologic and clinical information the health care providers have on hand. The commonly used respiratory samples for the influenza virus diagnosis include nasal aspirate or nasal wash and nasopharyngeal or nasal swab. The use of respiratory samples depends mainly on the kind of testing for the diagnosis of influenza infection. It is also important to collect the samples after three to four days of the onset of influenza symptoms. Viral culture testing provides results within 3-10 days, while the rapid influenza diagnostic test (RIDTS) provides results in almost 15 minutes.
Most of the tests that can be possible to do at the physician’s office for rapid influenza diagnoses are almost higher than 90% specific and 50-70% sensitive for detecting influenza virus. For this very reason, the chances of getting false-negative results are higher than getting false-positive results, particularly during the peak activity of the influenza virus in the community. The application of rapid molecular assays can give results in almost 20 minutes with high precision and sensitivity. Advancements in the molecular assays make it more available for the use and help produce the results in 60-80 minutes with very high precision and sensitivity. It is crucial to collect respiratory specimens as early as possible after the onset of influenza symptoms. The ideal time for collecting specimens is usually less than three days after the onset of influenza symptoms.
For the patients living in hospitals or other healthcare facilities having the suspicion of influenza and respiratory tract disease, the specimens from lower respiratory tracts can help detect influenza viruses using RT-PCR. As the viral shedding of influenza viruses is more detectable for a longer time in the lower respiratory tract than the upper respiratory tract, the specimens must be from the lower respiratory tract. If a patient is critically ill or is on mechanical ventilation, then you can collect the bronchioalveolar lavage fluid or endotracheal aspirate for influenza testing. Following is the description of some in practice diagnostic testing methods for the influenza virus:
Viral culture
As the outbreak of respiratory disorders happens, and the people get suspicious about influenza infection, some specimens from the respiratory tract are viable for molecular assays. After the testing of specimens by molecular assays, you can identify other illnesses too. It is essential for the determination of influenza A virus subtypes to collect samples from the respiratory tract. The viral culture helps detect the influenza A and B virus subtypes and the strains responsible for causing illness. Moreover, the use of viral culture also helps in surveillance of advancing virus strains that might need to include in the future vaccine. Through viral culture, the exact cause of respiratory infection also reveals.