Avian Influenza (5): Diagnosis

Lower respiratory tract manifestations develop early in the course of illness and are usually found at presentation. Respiratory distress, tachypnea,and inspiratory crackles are common. Sputum production is variable and sometimes bloody. Here the initial clinical picture of a viral pneumonitis can be complicated by bacterial superinfection or ARDS. Radiographic changes include diffuse, multifocal,or patchy infiltrates; interstitial infiltrates;and segmental or lobular consolidation with air bronchograms. Progression to respiratory failure has been associated with diffuse, bilateral, ground-glass infiltrates and manifestations of the acute respiratory distress syndrome (ARDS).

Diagnosis may be based upon a high index of clinical suspicion, and appropriate isolation measures can be undertaken. 4 main methods:

• Virus isolation
• Detection of viral proteins (e.g. by EIA)
• Detection of viral nucleic acids (PCR)
• Serology (IgM & IgG).

The EIA kits are widely available. They are all highly specific (>95%), but have variable sensitivity (60%->75%). Quickvue Immunoassay (Flu A & B) is the most accurate and rapid. H5N1 is classified as a select agent and must be worked with under CL3 laboratory conditions. Clinical specimens from suspected H5N1 cases may be tested by PCR assays using standard BSL 2 work practices in a Class II biological safety cabinet. In addition, commercial antigen detection testing can be conducted under BSL 2 levels to test for influenza. Real-time PCR assays may be employed.

Finally in the next part, we will examine the therapeutic options, "stockpiling", and clinical progression .

AMH