Laboratory personal conducting research on tuberculosis face the danger of being infected by aerosols of tubercle bacilli. Depending on the nature of the TB sample, biohazard safety cabinets are not always mandatory during this research. But lab personnel must conduct thorough risk assessments.
Laboratory bio safety is a combination of administrative controls, containment equipment practice and procedures. These enable staff to work safely with potentially dangerous microorganisms and prevent their exposure to dangerous pathogens. Laboratory manuals issued by the World Health Organisation (WHO) have identified different levels of tuberculosis (TB) testing that require different safety procedures.
There are three levels of risk associated with TB laboratories. There is a low TB risk where WHO concludes that biohazards safety cabinets need not be mandatory. There is a moderate TB risk which requires the use of contained working surfaces. The final group, a high TB risk where work requires the use of a state-of-the-art biohazard safety cabinet. The level of risk is determined by the probability of aerosols being generated from samples under investigation or culture. It has found that the likelihood of infectious TB aerosols being generated from sputum specimens is much lower that the likelihood of such aerosols being generated from liquid cultures. So the risks associated with handling sputum samples are lower than those for handling cultured material.
Laboratory safety cabinet use
A low risk laboratory may examine sputum specimens through direct smear microscopy. The production of aerosols from these specimens when opening a sputum container is much lower than those produced by a cough from an infected person. Work benches should be separate from any telephones or paper work and there should be good ventilation. Moderate risk laboratories process specimens for solid culture media and perform direct assays and microscopic observations. In this case, the processing of sputum samples should be performed in a biohazard safety cabinet. The proper use of cabinet procedures is vital. High risk TB laboratories manipulate TB cultures and suspensions of tubercle bacilli. Molecular assays and aqueous suspensions of TB bacilli should be performed in a state-of-the-art biohazard safety cabinet. The laboratory has to have two sets of entry doors so that there is an ante room to the containment laboratory.
Risk identification and assessment
Laboratory personnel should conduct a risk assessment prior to starting work. They should determine the suitability of the laboratory structure for such work, the proficiency of staff to follow safe practices and the integrity of safety equipment. All equipment should be tested regularly and certified, in particular a state-of-the-art biohazard safety cabinet. There should be a periodic review of all risky procedures and revised before a new experiment or procedures is introduced.
TB laboratories of moderate and high risk that use biohazards safety cabinets should follow strict housekeeping procedures. The cabinet should be connected to an uninterruptible power supply, the working area should be cleaned with alcohol before and after experiments and the HEPA filter in the cabinet should be tested regularly. The state-of-the-art biohazard safety cabinet should provide full protections to the laboratory’s personnel, to the samples under test and to the environment.
Helen Small is a research microbiologist specialising in infectious diseases. She advises on the use of biohazards safety cabinets and the types of risk where a state-of-the-art biohazard safety cabinet should be used.