Aerosols are droplets of liquid or solid particulates that are suspended in the air. Most of these are invisible to the human eye. Researchers working with infectious agents may cause accidental aerosol generation when using centrifuges, blenders, shakers, pipettes and other laboratory equipment.
Infectious agents may occur in any laboratory specimen from humans and animals. All research laboratories follow general universal precautions when handling human blood, body fluids or human cell lines that have been screened for pathogens. This is an approach to infection control that treats all human specimens as if they are known to be infectious with pathogens such as the Human Immunodeficiency Virus (HIV), Hepatitis B and C (HBV and HCV) and other blood borne pathogens. Animals also harbour pathogens that are virulent for humans. Samples of blood and fluids should be treated in an analogous manner as with human samples. However, laboratory animals may also excrete micro-organisms and allergens that cause human diseases after bites, scratches or excretions. Laboratory plant specimens may also release infectious or contaminating micro-organisms when improperly handled.
Special considerations are needed when examining human and animal cell cultures in a research laboratory. The first step is that all investigations should be performed in a biohazard safety cabinet that provides the correct containment for the specimen’s risk category. There are four such risk groups.
– Risk Group 1 is not associated with any diseases in healthy adult humans. An example is E-coli K-12.
– Risk Group 2 cause diseases to humans that are rarely serious and for which preventative treatments are readily available such as Salmonella.
– Risk Group 3 pathogens are associated with serious or lethal human diseases for which medical treatments may be available such as Mycobacterium Tuberculosis.
– Risk Group 4 pathogens cause lethal or serious human infections for which treatment may not be available such as Ebola virus or Monkey B virus.
Researchers handling infectious micro-organisms should perform all aerosol generating procedures, shaking, grinding, blending sonicating etc, in the biohazard cabinet. They should never mouth pipette samples but always use mechanical pipetting. No infectious material should be expelled forcibly from a pipette. Stoppers and covers of vessels containing samples should be removed slowly and never popped or removed after the container has been shaken. Gasket-sealable tubes and rotors should be used during all centrifuging. Tubes and containers with screw on tops should be used.
Accidental Aerosol Generation
The accidental spillage of materials is an obvious hazard that may generate aerosols. There is also an increased risk of aerosols when large volume samples are being investigated. If an aerosol has been created the researcher should leave the area calmly and allow the aerosols to settle. After this, a cloth with disinfectants should be placed over the work surface. This will deactivate any droplets that could be infectious agents.
Laboratory researchers handling human or animal cell cultures in a biohazard safety cabinet must use strict safety procedures when handling pathogens to avoid the generation of aerosols. Such aerosols may cause infections through inhalation, ingestion from contaminated hands or equipment and self-inoculation through accidental incisions.
Helen Worthing is a microbiologist working in the investigation of auto immune diseases. She has assisted in the design of special types of high quality biohazard safety cabinet.