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Biosafety Levels in Laboratories – What is the Difference?

In this 2012 photo, veterinarian Nadia F. Gallardo-Romero, DVM is suited up for work in a BSL-4 lab. Credit: CDC

In July 2019, the United States Army Medical Research Institute of Infectious Disease (USAMRIID) ceased research operations after failing to meet biosafety requirements. USAMRIID is the lead research institute and only biosafety level (BSL) 4 laboratory for the Department of Defense that conducts medical biological research on high-risk pathogens. To better understand the implications of USAMRIID having their operations discontinued, it is critical to identify what a BSL is and how each level is designated.

The United States is home to several types of laboratories that conduct medical research on a variety of infectious biological agents to promote the development of new diagnostic tests, medical countermeasures, and treatments. To promote safe medical research practices in laboratories studying infectious agents, the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health have established four BSLs. The levels consist of requirements that have identified as protective measures needed in the laboratory setting to ensure the proper management of infectious agents to avoid accidental exposure or release into the environment.

The BSL designations, ranked from lowest to the highest level of containment, are BSL-1, BSL-2, BSL-3, and BSL-4. The BSL designations outline specific safety and facility requirements to achieve the appropriate biosafety and biocontainment. The BSL is assigned based on the type of infectious agent on which the research is being conducted. The CDC has designed an infographic to help visualize the differences between each level. Each level builds on the previous level, adding additional requirements.

  • Biosafety Level 1 (BSL-1): Conducts research on agents that are not known to consistently cause disease in healthy adults (e.g., Bacillus subtilis, Naegleria gruberi, and non-pathogenic E. coli species). This type of BSL laboratory follows standard microbiological practices and requires the fewest precautions due to the agents posing minimal risk to laboratory personnel. A BSL-1 laboratory is not isolated from general builds or human traffic. This level is found in undergraduate and secondary educational training and teaching laboratories.
  • Biosafety Level 2 (BSL-2): Conducts research on indigenous agents that are present in the community and associated with human disease posing a moderate-risk (e.g., HIV, hepatitis B virus, and Salmonella species). This level is appropriate for research on any human-derived blood, bodily fluids, tissues, or human cells in which the presence of an infectious agent may be unknown. Access to a BSL-2 laboratory is restricted to trained personnel while research is being conducted. This level is found in clinical, diagnostic, and teaching laboratories.
  • Biosafety Level 3 (BSL-3): Conducts research on indigenous or exotic agents with potential for respiratory transmission, which may cause serious or potentially lethal infection (e.g., Mycobacterium tuberculosis, Francisella tularensis, St. Louis encephalitis virus). Due to the type of agents being handled, access is controlled in a BSL-3 laboratory with a corridor that has two self-closing separating access from the lab. This laboratory is also housed in a building with special engineering safety features. This level is found in clinical, diagnostic, teaching, and research laboratories.
  • Biosafety Level 4 (BSL-4): Conducts research on dangerous and exotic agents with a high-risk of causing life-threatening disease, the possibility of aerosol transmission, and no known treatment or therapy (e.g., Marbug virus, Congo-Crimean virus, Ebola virus). Entry into the BSL-4 laboratory is secure and limited, monitoring all persons in the facility with a logbook. Laboratory personnel are required to complete a clothing change prior to entry and shower on exit. This laboratory is customarily in a separate building or isolated area with complex engineering safety features, such as filtered ventilation systems and strict waste management requirements to prevent the release of an agent. The construction of the build forms a sealed internal shell for maximum containment. This level is found in select research laboratories.

The implications of having the BSL-3 and BSL-4 laboratories at USAMRIID suspended due to biosafety issues affect the Laboratory Response Network, thereby potentially straining the nation’s biopreparedness infrastructure. USAMRIID is one of three national laboratories responsible for specialized characterization of organisms and select agents. Adherence to BSL requirements is paramount to maximize the safety of laboratory personnel, the community, and ultimately the nation. Since mid-August, there have been no updates regarding the discontinued research operations at USAMRIID.

Note: This summary is neither extensive nor exhaustive of the requirements for each BSL. For additional information about BSL requirements, please see the Biosafety in Microbiological and Biomedical Laboratories guide by the U.S. Department of Health and Human Services.

Frankie Catalfumo is an epidemiologist with experiencing leading emergency preparedness and response operations in support of the federal government and international agencies relating to emerging infectious diseases and natural disasters. During his career, he has supported the Centers for Disease Control and Prevention, the Department of Defense, and the Pan American Health Organization to strengthen and enhance global health security.

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