The four-tier classification system of biosafety levels (1–4) described in WHO’s Laboratory biosafety manual² provides broad guidance on basic concepts of biosafety for the development of national and international codes of practice. The challenge for managers of TB programmes and staff at laboratories, particularly in resource-limited settings, has been to interpret the generic risk-group assignments and biosafety levels into specific precautions relevant to a country’s activities. As a result, the use of biosafety levels 1–4 when describing the needs of TB laboratories has led to confusion about what precautions are necessary.
Decisions about which are the most appropriate biosafety measures for a specific laboratory should be undertaken using an approach based on risk assessment that considers the different types of procedures performed by the laboratory. Risk assessments require careful judgement: on the one hand, underestimating risks may lead to biosafety hazards but, on the other hand, safeguards that are more rigorous than actually needed may impose unnecessary burdens – both financial and in terms of human resources – on a laboratory’s staff and management.
The risk-assessment approach for a TB laboratory considers:
- the bacterial load of materials (such as sputum specimens and cultures), and the viability of TB bacilli;
- route of transmission of TB;
- whether the material handled and the manipulations required for each procedure are likely to generate infectious aerosols;
- the number of manoeuvres for each technique that may potentially generate aerosols;
- the workload of the laboratory and individual staff members;
- the location of the laboratory;
- the epidemiology of the disease and the patient population served by the laboratory;
- the level of experience and the competence of the laboratory’s technicians;
- the health of the laboratory’s workers(especially HIV-positive technicians).
In addition, the ability of laboratory staff to control hazards must be considered. Their ability will depend on the competence, technical proficiency, and microbiological practices of all laboratory technicians; the operational integrity of containment equipment; the facility’s safeguards; and the availability and proper use of appropriate standard operating procedures. Box 1 provides details on conducting a procedural risk assessment. Table 1 and Table 2 summarize the considerations used to assess risks for TB laboratories in general, and risks associated with performing different procedures in TB laboratories. These considerations were used by the Expert Group to determine the minimum biosafety requirements necessary for performing different procedures in TB laboratories.
The laboratory manager is responsible for ensuring that the minimum biosafety precautions are implemented as described in this manual, and that appropriate standard operating procedures, equipment and facilities are available to support the work being undertaken. The laboratory’s biosafety precautions should be reviewed periodically and revised when necessary, particularly after new procedures or techniques are introduced.
To ensure the safest possible conduct of work, the results of risk assessments should dictate the appropriate laboratory equipment, personal protective equipment and design features of the facilities which need to be incorporated into the standard operating procedures for each procedure undertaken in the laboratory,