Part II: Microscopy
specimen handling

Receipt of incoming specimens
Specimens should be received at a separate specimen delivery counter and the following procedures applied:

• Wear disposable gloves, if available, during receipt and inspection of incoming  specimens
• Inspect the delivery box for signs of leakage. If mass leakage is evident discard the  box by autoclaving or burning
• Disinfect the outside of the delivery box using cotton wool or paper towels saturated with a suitable disinfectant (eg. 5% phenol)
• Open the delivery box carefully and check for cracked or broken specimen containers. Autoclave or burn these without processing and request another specimen
• Check that specimens have been adequately labelled with individual identification  numbers and that these correspond with the numbers on the accompanying list
• Note the relevant patient and specimen details into the laboratory register
• Disinfect the inside of the delivery box, discard gloves and wash hands after handling specimen containers

Safe handling of specimens
Transmission of M. tuberculosis results essentially from infectious aerosols, ie. droplet nuclei of 1-5Fm in diameter containing tubercle bacilli, sufficiently small to reach lung alveoli and initialise an infection.

Infection control in the microscopy laboratory must aim at reducing the production of aerosols. Good ventilation is necessary for the protection of laboratory staff from infectious airborne nuclei. A simple way to ensure ventilation and directional airflow is by properly placed windows and doors.

Microscopy procedures differ considerably in their potential to create aerosols:

Specimen collection
Tuberculosis suspects are sometimes referred directly to the laboratory for sputum collection. This practice exposes laboratory workers to a high risk of infection by aerosols produced during collection procedures. Precautions to lower this risk include instructing tuberculosis suspects to cover their mouths while coughing, standing behind (and not in front of) coughing individuals and collecting specimens outdoors where aerosols are diluted and sterilised by direct sunlight.

Smear preparation
While opening sputum containers and preparing smears may produce aerosols, these manipulations entail less risk of transmission than unprotected coughing. There is very little epidemiological evidence that preparing sputum smears is correlated with an increased risk of tuberculosis infection. Expensive and sophisticated equipment is no substitute for good laboratory practice, and biological safety cabinets are therefore not mandatory in peripheral laboratories performing smear microscopy only.

Evaluation of sputum quality and volume
A good sputum specimen consists of recently-discharged material from the bronchial tree, with minimum amounts of oral or nasal material. Satisfactory quality implies the presence of mucoid or mucopurulent material and is of greater significance than volume. Ideally, a sputum specimen should have a volume of 3-5ml, although smaller quantities are acceptable if the quality is satisfactory. Induced sputum resemble saliva and it is important that these specimens not be discarded as unsuitable.