Influenza and diagnostic testing
What is influenza?
Flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can lead to death. The best way to prevent flu is by getting a flu vaccine each year
Influenza and diagnostic testing
Sign and Symptoms
Influenza (flu) can cause mild to severe illness, and at times can lead to death. Flu symptoms usually come on suddenly. People who have flu often feel some or all of these symptoms:
- Fever or feeling feverish/chills (not everyone with flu will have a fever).
- Cough
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Headaches
- Fatigue (tiredness)
- Some people may have vomiting and diarrhea, though this is more common in children than adults
INFLUENZA AND DIAGNOSTIC TESTING
What is the difference between Influenza (Flu) and COVID-19?
Compared with flu, COVID-19 can cause more severe illness in some people. Compared to people with flu, people infected with COVID-19 may take longer to show symptoms and may be contagious for longer periods of time.
You cannot tell the difference between flu and COVID-19 by the symptoms alone because they have some of the same signs and symptoms. Specific testing is needed to tell what the illness is and to confirm a diagnosis. Having a medical professional administer a specific test that detects both flu and COVID-19 allows you to get diagnosed and treated for the specific virus you have more quickly. Getting treated early for COVID-19 and flu can reduce your risk of getting very sick. Testing can also reveal if someone has both flu and COVID-19 at the same time, although this is uncommon. People with flu and COVID-19 at the same time can have more severe disease than people with either flu or COVID-19 alone.
INFLUENZA AND DIAGNOSTIC TESTING
Influenza Diagnosis: Laboratory Diagnostic Procedures
A number of tests are available for influenza diagnosis, for better assistance in making the right diagnostic and treatment decisions. From a clinical standpoint, the ability to determine if influenza is the cause of outbreak in a closed setting (e.g., hospital, nurseries) is particularly useful.
Sensitivity, specificity, test difficulty, length of time, and special equipment requirements vary between the tests (Table 1). Available diagnostics tests include viral culture, serology, rapid antigen testing, reverse transcription polymerase chain reaction (RT-PCR), immunofluorescence assays, and rapid molecular assays.
Table 1 Test characteristics
For the rapid influenza diagnostic test (RIDT), preferred respiratory samples for influenza testing include nasopharyngeal or nasal swab. Samples should be collected within the first 3-4 days of illness. To maximize detection of influenza viruses, respiratory specimens should be collected as close to illness onset as possible (ideally less than 3-4 days after onset).
Rapid influenza diagnostic tests are normally antigen detection assays. Detection of influenza viral antigen in respiratory specimen can be performed within 15 minutes with low to moderate sensitivity and high specificity. Different types of rapid influenza diagnostic tests are available, depending on purpose of use. Different tests can detect 1) only influenza A viruses; 2) both influenza A and B viruses, but not distinguishing between the two types; or 3) both influenza A and B viruses and distinguishing between the two. None of the tests can detect Influenza A virus subtypes.
Due to the lower sensitivity of the rapid influenza diagnostic tests, physicians should consider confirming negative test results with RT-PCR, viral culture or other means, especially in hospitalized patients or during suspected institutional influenza outbreaks, to account for the possibility of false-negative RIDT results, especially during periods of peak community influenza activity. In contrast, false-positive RIDT results are less likely, but can occur during periods of low influenza activity. Therefore, when interpreting results of a rapid influenza diagnostic test, physicians should consider the positive and negative predictive values of the test in the context of the level of influenza activity in their community. Package inserts and the laboratory performing the test should be consulted for more details regarding use of rapid influenza diagnostic tests.
Source: CDC. 2020. Influenza Signs and Symptoms and the Role of Laboratory Diagnostics.
INFLUENZA AND DIAGNOSTIC TESTING
K-Influenza A/B Antigen Test (K. Biosciences)
1. Product overview
- For the detection of Influenza A and Influenza B nucleocapsid protein antigen
- Specimens: nasopharyngeal swab directly collected from suspected flu infection within 3-7 days after symptom onset
- Based on lateral flow immunoassay with qualitative detection
- For in vitro diagnostic only
- For professional use
- Manufactured under ISO13485
2. Test principle
The K-Influenza A/B Antigen Test is a colored chromatographic immunoassay. After extraction, the sample is dropped on sample pad, and the buffer flows through the conjugate pad containing anti-nucleocapsid conjugated gold nanoparticle. If the sample contains Influenza A/B viral nucleocapsid antigen, the antigen binds to the conjugate to form an anti-nucleocapsid gold conjugate–nucleocapsid complex. The complex flows to the test line coated with anti-nucleocapsid antibody, leading to the formation of an anti-nucleocapsid gold conjugate–nucleocapsid–anti-nucleocapsid complex, which will produce a visible color on the test line.
3. Test procedure
4. Test interpretation
Negative for Influenza A and B: The presence of only one control line (“C” band).
Interpretation: No infection or early infection of influenza A and B infection. No Influenza A and B nucleocapsid antigens are detected.
Positive for Influenza A: The presence of two colored lines: the control “C” band and the “A” bands.
Interpretation: Influenza A nucleocapsid antigen is detected.
Positive for Influenza B : The presence of two colored lines: the control “C” band and the “B” bands.
Interpretation: Influenza B nucleocapsid antigen is detected.
Positive results indicate the presence of Influenza A or Influenza B antigens in the tested specimen. To ensure the accuracy of the results, real time-PCR assay should be performed further as a confirmatory test, or other methods as described in national laws and regulations.
Negative results indicate no Influenza A or Influenza B antigens in the tested specimen, but the possibility of influenza infection is not excluded. Duration of infection, patient history, signs and symptoms need to be considered for diagnosis.
5. Provided materials
One box of K-Influenza A/B Antigen Test contains the following items:
- Individually foil-pouched test cassettes, with a desiccant (25 packs)
- Sample extraction buffer in a sample extraction tube (25 tubes)
- Sterile nasopharyngeal swab (25 pieces)
- Paper rack (1 piece)
- Instruction for use
