WHO Guidelines For Laboratory Diagnosis Of Avian Influenza Infection - 1

General information
Respiratory virus diagnosis depends on the collection of high-quality specimens, their rapid transport to the laboratory and appropriate storage before laboratory testing. Virus is best detected in specimens containing infected cells and secretions. Specimens for the direct detection of viral antigens or nucleic acids and virus isolation in cell cultures should be taken preferably during the first 3 days after onset of clinical symptoms.

Type of specimens
A variety of specimens are suitable for the diagnosis of virus infections of the upper respiratory tract:

•nasal swab
•nasopharyngeal swab
•nasopharyngeal aspirate
•nasal wash
•throat swab.

In addition to swabs from the upper respiratory tract, invasive procedures can be performed for the diagnosis of virus infections of the lower respiratory tract where clinically indicated:

•transtracheal aspirate
•bronchoalveolar lavage
•lung biopsy
•post-mortem lung or tracheal tissue.

Specimens for the laboratory diagnosis of avian influenza A should be collected in the following order of priority:

•nasopharyngeal aspirate
•acute serum
•convalescent serum.

Specimens for direct detection of viral antigens by immunofluorescence staining of infected cells should be refrigerated and processed within 1–2 hours. Specimens for use with commercial near-patient tests should be stored in accordance with the manufacturer’s instructions. Specimens for virus isolation should be refrigerated immediately after collection and inoculated into susceptible cell cultures as soon as possible. If specimens cannot be processed within 48–72 hours, they should be kept frozen at or below –70 °C.

Respiratory specimens should be collected and transported in virus transport media. A number of media that are satisfactory for the recovery of a wide variety of viruses are commercially available.

Procedures for specimen collection
Materials required
•Sputum/mucus trap
•Polyester fibre-tipped applicator
•Plastic vials
•Tongue depressor
•15-ml conical centrifuge tubes
•Specimen collection cup or Petri dishes
•Transfer pipettes

Virus transport medium
(A) Virus transportation mediumfor use in collecting throat and nasal swabs

•Add 10 g veal infusion broth and 2 g bovine albumin fraction V to sterile distilled water (to 400 ml).
•Add 0.8 ml gentamicin sulfate solution (50 mg/ml) and 3.2 ml amphotericin B (250 μg/ml)
•Sterilize by filtration.

(B) Nasal wash medium
1. Sterile saline (0.85% NaCl).

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