Microbiology

Respiratory Specimens

Sputum

The specimen required is sputum from the lower respiratory tract produced by deep coughing. If the cough is dry, physiotherapy, postural drainage or inhalation of an aerosol before coughing may be helpful. Saliva and postnasal secretions are not suitable. Sputum may be cultured up to 48hrs after collection, if refrigerated, but interpretation of results should be made with care.

If TB is suspected, early morning specimens for examination of Mycobacterium spp. should be collected on at least 3 consecutive days.

Culture for M. tuberculosis, Actinomyces, Legionella or Aspergillus sp. will not be undertaken routinely. If indicated please state on the request form.

Bronchoalveolar lavage (BAL)

A flexible bronchoscope is inserted and a segment of lung is “washed” with sterile saline and then aspirated, thus allowing recovery of both cellular and non-cellular components of the epithelial surface of the lower respiratory tract.

Non directed bronchoalveolar lavage (NBL)

A suction catheter is passed down the endotracheal tube until resistance is met. An aliquot of sterile saline is injected and then aspirated.

BAL / NBL specimens are particularly useful in the diagnosis of Pneumocystis carinii pneumonia, pneumonia caused by Legionella pneumophila, and for the detection of Mycobacterium tuberculosis presenting as pneumonia.

It is essential that relevant clinical details are provided, or cases are discussed with a microbiologist, to ensure appropriate laboratory investigations are undertaken.

If Legionnaires disease is suspected please ensure sterile water is used to perform the BAL, as normal saline may reduce organism recovery.

Bronchial aspirate

These are collected by direct aspiration of material from the large airways of the respiratory tract by means of a flexible bronchoscope.

Bronchial washings

Bronchial washings are collected in a similar fashion to bronchial aspirates, but the procedure involves the aspiration of a small amount of instilled saline from the large airways of the respiratory tract.

Bronchial brushings

This uses a protected brush catheter in the bronchoscope to tease material from the airways.

Tracheal aspirate

Tracheal aspirates are collected via the endotracheal tube.

Nasal Swab

A plain sterile swab should be used to sample anterior nares, gently rotating the swab on the surface, if necessary moisten the swab with sterile water or saline before swabbing.

Pernasal Swabs

Special fine wire swabs for the isolation of B. pertussis and N. meningitidis are available from the laboratory.

Postnasal aspirate is the preferred specimen for the isolation of B. pertussis. Please inform the laboratory before sending these specimens.

Postnasal Swabs

Swabs for the isolation of N. meningitidis. The specimen is taken by wiping the swab across the posterior pharynx as high up behind the uvula as possible. Culture should be carried out as soon as possible.

Throat Swabs

Taken by wiping the swab across the tonsillar area and/or posterior pharynx avoiding the tongue and uvula. Where there is pus or membrane is visible, these should be swabbed.