Testing for novel influenza A (H1N1) virus

Testing for novel influenza A (H1N1) virus

Influenza A (H1N1) virus is the subtype of influenza A virus that was the cause of pandemic human influenza (flu) in 2009. This is also called novel influenza A (H1N1) or Swine flu.

It is recommended to test suspected cases of swine flu, especially those with severe illness, by obtaining an upper respiratory specimen.

 Available tests

Real-time RT-PCR is the most sensitive test that is recommended for confirmation of novel influenza A (H1N1) cases (Center for disease control and prevention, USA).

Novel influenza A (H1N1) virus will also test positive for influenza A

 (approx pricing

PCR         =  Rs 7500/-

Rapid Test  =  Rs 2900/-)

Rapid test for Influenza Antigen A/B/H1N1 – a chromatographic immunoassay for rapid detection of Influenza A/B/H1N1. The sensitivity of this test compared to RT-PCR is ~ 75%

Note: Negative test results obtained from rapid influenza diagnostic tests (RIDTs) that detect influenza viral antigens do not exclude influenza virus infection in patients with signs and symptoms of influenza. A negative test result could be a false negative and should not preclude further diagnostic testing (such as RT-PCR) and starting empiric antiviral treatment

Preferred respiratory specimens

The following should be collected as soon as possible after illness onset:

  • Nasopharyngeal swab, nasal aspirate or a combined nasopharyngeal swab with oropharyngeal swab. If these specimens cannot be collected, a nasal swab or oropharyngeal swab is acceptable.
  • For patients who are intubated, an endotracheal aspirate should also be collected. Bronchoalveolar lavage (BAL) and sputum specimens are also acceptable.

 Specimen collection

Nylon swabs and viral transport media provided by the testing laboratories should be used for specimen collection for PCR tests. Regular cotton swabs are not suitable, and result in reaction inhibition.

 Nasopharyngeal Swab

1. Tilt patient’s head back 70 degrees.

2. Insert swab into nostril. (Swab should reach depth equal to distance from nostrils to outer opening of the ear.) Leave swab in place for several seconds to absorb secretions.

3. Slowly remove swab while rotating it. (Swab both nostrils with same swab.)

Oropharyngeal swab – please use special nylon swabs provided by the Molecular lab

1. Tilt patient’s head back 70 degrees.

2. Insert swab into mouth, and swab the posterior pharynx and tonsillar areas. (Avoid the tongue).

Specimen transport

a) If the specimen can be immediately transported to the testing lab with a frozen cold pack – Place tip of swab into a dry sterile tube and snap/cut off the applicator stick at the breakpoint in the middle. Cap the tube tight. Place in a fridge or maintain on ice pending transport.  Use a frozen gel pack during transport.

 b) If the specimen cannot be transported within 8 hrs – Place tip of swab into a tube with viral transport media and snap/cut off the applicator stick at the breakpoint in the middle. Cap the tube tight. Keep specimen refrigerated prior to transport. Transport the specimen as soon as practical within 3-4 days.