How many internationally recognized biosafety levels are there?

There are four internationally recognized biosafety levels (BSL-1 to BSL-4).

These levels are defined by the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) and are widely adopted by laboratories worldwide, including in WHO and national public health systems.

The classification is based on:

The pathogenicity of the microorganisms handled

The mode of transmission (e.g., airborne, direct contact)

The availability of treatment or vaccines

The potential risk to personnel, the environment, and the public

The biosafety levels include:

BSL-1: Basic level of protection for low-risk agents that do not cause disease in healthy humans.

BSL-2: Intermediate containment for moderate-risk agents associated with human disease.

BSL-3: High containment for pathogens that may cause serious or potentially lethal disease via inhalation.

BSL-4: Maximum containment for life-threatening agents with no known treatment or vaccine.

These biosafety levels form a globally accepted framework for laboratory safety and biosecurity in microbiological and biomedical research.