The most common lab-acquired viral infection is due to the hepatitis B virus (HBV; 3-4 infections/1000 handlers) although lab-acquired infections due to other viruses have been reported (e.g., SARS, Marburg, Vaccinia, West Nile, Ebola)1,2. The fundamental focus in the safe handling of viruses is viral containment that protects lab personnel and the surrounding environment. Biological safety cabinets (biosafety cabinets) come in several classes (I, II, and III) that offer varying levels of protection from hazardous or contagious materials. For all classes of biological safety cabinet, the air is HEPA filtered before leaving the system as exhaust. A Class I biosafety cabinet is designed to protect the user and the environment, not the sample as negative pressure is used to pull outside air in across the workspace.
Although there are a wide variety of BSCs available, the most commonly used BSC is the Class II Type A2 BSC (Fig 1). Class II biological safety cabinets are divided into four subtypes (A1, A2, B1, and B2) and have the additional feature of protecting the sample as the air supply is HEPA-filtered before passing over the workspace. The Class II subtypes are differentiated by the amount of recirculated air within the cabinet. Class III biosafety cabinets (also known as gloveboxes) provide maximum protection for work in biosafety level 4 containment labs. A class III biosafety cabinet is a hermetically-sealed glovebox with access through a dunk tank or double-door box that allows for decontamination.
Safe handling of a virus in a BSC requires additional good microbiological laboratory practices3. The use of hypodermic needles and syringes should be limited to removing fluid from diaphragm-stopped test tubes or inoculation of animals. Hypodermic needles should never be removed from their syringe or re-capped in order to prevent accidental self-inoculation. Use mechanical pipetting methods only (i.e., do not mouth pipette although this practice has long been eliminated). Pipettes should be emptied of their contents gently with the tip against the inner wall of the receiving tube and the contents should not be expelled forcibly.
All workbench areas should be appropriately sanitized before and after manipulating viral samples. Lab workers should wear personnel protection equipment (PPE; e.g., masks, respirators, eye shields, gowns, gloves, shoe coverings) which should be removed before leaving the lab. This ensures that street clothing is protected from viral contamination. A mask or face shield may be especially useful to protect against accidental face touching that could result in viral infection via the mucous membranes. Proper sealing of test tube caps should be monitored carefully since aerosols or droplets are produced during vortexing, sonicating, mixing, or shaking. Specimens that require centrifugation should be placed in securely capped containers before leaving the BSC and then placed in a centrifuge equipped with sealed-buckets since the potential for extensive contamination during high-speed operation is great if any fluid should escape.
Since the production of aerosols is an important source of lab-acquired viral infections, an assessment of the level of aerosol spread can be monitored by using a sham specimen containing fluorescein that is processed exactly in the same way as the viral specimen. The spread of fluorescein at key locations can be determined by ultraviolet light. Any accidental spillage of a viral specimen should be promptly cleaned with an appropriate disinfectant. After work is completed, contaminated materials should be disposed of in biohazard containers or autoclaved and completed, re-usable lab equipment (e.g., pipettes, test tube racks, etc) should be cleaned with appropriate disinfectant.
References:
1. Artika, IM and Ma’roef CN: Laboratory biosafety for handling emerging viruses. Asian Pacific Journal of Tropical Biomedicine, 7(5):483, 2017.
2. Hewlett AL et al: Ebola Virus Disease: Preparedness and infection control lessons learned from two biocontainment units. Curr Opin Infect Dis, 28(4):343, 2015
3. Tierno PM: Preventing acquisition of HIV in the laboratory: Safe handling of AIDS specimens. Lab Medicine 17 (11): 696, 1986