When a patient presents a troubling cough, doctors will often request a sputum sample, which will be sent off for laboratory analysis. A biohazard safety cabinet is an essential piece of equipment in any clinical laboratory which handles sputum samples, as many pathogenic bacteria are spread by airborne contamination, including the mycobacteria responsible for tuberculosis (TB).
In 2005, TB had become so rare in the UK that routine BCG vaccinations were discontinued. However, there has since been a sharp rise in reported cases of the disease, partly from people emigrating from areas where it is still rife. The bovine form of the disease (M. bovis) can also be contracted by humans, as it is zoonotic. TB is easily passed on through inhalation of aerosolised droplets containing the bacterium, such as those produced by coughing or sneezing (although M.bovis can also be transmitted by ingestion of milk products.) Although most sputum samples are TB-negative, they must still be treated as potentially infected.
Infection by aerosol
The risk of LAI (laboratory acquired infection) is extremely high for laboratory personnel handling samples potentially infected with TB bacteria, which also carry an environmental risk.
To get a definite diagnosis of any bacterial pulmonary infection, the microbes must first be isolated and identified. A sputum sample is one way of doing this. A microscopical smear examination will identify any bacteria present (although this on its own does not negate bacterial infection), after which the sample is cultured. This allows a more accurate analysis, giving clinicians important information, such as whether it is a drug-resistant strain or not.
The biosafety regulations are extremely strict for human pathogens, with specific criteria for sputum samples suspected of harbouring M. tuberculosis. Minimum requirements for preliminary analysis and culturing are a BSL-2 level of containment, using BSL-3 procedures and equipment. All further research must be performed at BSL-3. A biological safety cabinet must be used for all procedures.