INVC,
Delhi,
Not all individuals with suspected pandemic H1N1 influenza A need to have the diagnosis confirmed, particularly if the illness is mild said Padamshri & Dr. BC Roy National Awardee, Dr. KK Aggarwal, President Heart Care Foundation of India & National Vice President Elect IMA. The recommended test for suspected cases is real-time reverse transcriptase (RT)-PCR for influenza A, B, H1, and H3, which is generally performed at a state health department laboratory. To establish the diagnosis of pandemic H1N1 influenza A, an upper respiratory sample (nasopharyngeal swab, nasal swab, throat swab, combined oropharyngeal/ nasopharyngeal swab, or nasal aspirate) should be collected.
Whom to test — Testing for pandemic H1N1 influenza A should be considered in individuals with an acute febrile respiratory illness (a measured temperature of 100ºF or higher and recent onset of at least one of the following: rhinorrhea, nasal congestion, sore throat, or cough) or sepsis-like syndrome.
Priority for testing should be given to:
Those who require hospitalization and those who are at high risk for severe complications.
Specimens — To establish the diagnosis of pandemic H1N1 influenza A, an upper respiratory sample (nasopharyngeal swab, nasal swab, throat swab, combined ropharyngeal/ nasopharyngeal swab, or nasal aspirate) should be collected.
In intubated patients, an endotracheal aspirate should also be obtained. Swabs with a synthetic tip (eg, polyester or Dacron) and an aluminum or plastic shaft should be used. Swabs with cotton tips and wooden shafts are not recommended. Swabs made of calcium alginate are not acceptable. The collection vial in which the swab is placed should contain 1 to 3 mL of viral transport media. Specimens should be placed in viral transport media and placed on ice (4ºC) or refrigerated immediately for transportation to the laboratory. Once the samples arrive in the laboratory, they should be stored either in a refrigerator at 4ºC or in a -70ºC freezer. If a -70ºC freezer is not available, they should be kept refrigerated, preferably for ≤1 week. Specimens should be shipped on dry ice to the state public health laboratory.
Recommended tests
The recommended test to confirm the diagnosis of pandemic H1N1 influenza A virus is real-time reverse transcriptase (RT)-PCR for influenza A, B, H1, and H3.
Rapid antigen tests — Clinicians may consider using rapid influenza antigen tests as part of their evaluation of patients suspected of having pandemic H1N1 influenza A, but results should be interpreted with caution.
Confirmation of pandemic H1N1 influenza A infection can only be made by real-time reverse-transcriptase (RT)-PCR or culture.
Certain rapid influenza antigen tests that are commercially available can distinguish between influenza A and B viruses. Thus, a patient with only influenza B virus infection would not be suspected of having pandemic H1N1 influenza A virus infection. In contrast, a patient with a positive rapid antigen test for influenza A may be considered a probable case if he or she meets the other criteria. A negative rapid influenza test does not exclude infection.
