In 2004, the Centers for Disease Control and Prevention (CDC) launched experiments designed to combine the H5N1 virus and human flu viruses and then see how the resulting hybrids affected animals so that they could assess the chances that such a "reassortant" virus might emerge and determine how dangerous it would be.

Their reasoning was that the worst fears of infectious disease experts - that the H5N1 avian influenza virus  circulating in parts of Asia might combine with a human-adapted flu virus, namely if someone with a flu virus also contracted the avian virus - might result in a deadly new flu virus that could spread around the world.   A pandemic of the kind not seen in almost a hundred years.

Because of the risks in creating viruses with the potential to spark a pandemic, the work was done in a biosafety level 3 (BSL-3) laboratory at the CDC in Atlanta.    People are always concerned that something may have been created in research that has contaminated outside areas so the biosafety levels, compiled from CDC documents, are outlined below.


From the earliest days of microbiological research, laboratorians have recognized that acquiring infections from the agents they manipulated was a recognized occupational hazard.   The most commonly-acquired lab infections were caused by bacterial agents; as microbiologists learned to culture animal viruses, they also found ways to become infected with these agents .

Guidelines evolved as a means of protecting microbiological workers based on these data and an understanding of the risks associated with various manipulations of many agents transmissible by different routes. These guidelines work from the premise that safe work sites result from a combination of engineering controls, management policies, work practices and procedures and, occasionally, medical interventions. The different biosafety levels developed for microbiological and biomedical laboratories provide increasing levels of personnel and environmental protection.

 Crucial to safe working conditions are the various types of specialized equipment available to serve as primary barriers between the microorganism and the laboratorian. These range from simple gloves and other personnel protective equipment to simple (sealed centrifuge heads) or complex (biosafety cabinets) containment devices.

Biosafety Level 1

BSL-1 is appropriate for working with microorganisms that are not known to cause disease in healthy human humans. This is the type of laboratory found in municipal water-testing laboratories, in high schools, and in some community colleges teaching introductory microbiology classes, where the agents are not considered hazardous . The lay-out of a typical BSL-1 laboratory is shown below. 

There is a door that can be closed to keep visitors out of the lab while work with the agents is in progress. Hazard warning signs may be posted on the door indicating any hazards that may be present, including radioactive materials, lazar lights, high noise emitting equipment, or toxic chemicals. There is a hand-washing sink available, preferably near the door.

 Persons working in the lab should wear a lab coat  to protect their street clothes. It is a recommended practice to wear gloves while manipulating the agents. Additional protective equipment may include working behind a splatter shield or wearing eye or face protection. At BSL-1, no special precautions are needed.

Hand washing is one of the most important procedures that can be used by laboratorians to prevent removal of unwanted microbiological agents, radioactive materials, or chemicals from the laboratory environment. Use of liquid soap is generally preferable to bar soap; twenty seconds of vigorous lathering will remove most of these materials very effectively. 

Biosafety Level 2

The agents manipulated at BSL-2 are often ones to which the workers have had exposure to in the community, often as children, and to which they have already experienced an immune response. Unlike the guidelines for BSL-1, there are a number of immunizations recommended before working with specific agents. Most notable is Hepatitis B virus immunization which is recommended by the Occupational Safety and Health Administration for persons, including laboratorians, at high risk of exposure to blood and blood products.

The supervisor of a BSL-2 laboratory should be a competent scientist who has a technical understanding of the risks associated with the microbiological agents in use. The supervisor limits access to those persons who have received the appropriate immunizations and establishes the personal protective standards for the laboratory; he/she is also responsible for developing the lab’s biological safety manual. Laboratory personnel should be aware of the potential hazards associated with the work and be proficient in the specified practices and procedures.

Biosafety Level 3

BSL-3 is suitable for work with infectious agents which may cause serious or potentially lethal diseases as a result of exposure by the inhalation route. BSL-3 laboratories should be located away from high-traffic areas. Examples of agents that should be manipulated at BSL-3 are M. tuberculosis (research activities), St. Louis encephalitis virus, and Coxiella burnetii.

The current main BSL-3 laboratories are located in a unique high containment building.   BSL-3 laboratories are characterized by having a double-door entry (shown here as an ante-room; other configurations are also used). Because the agents manipulated at BSL-3 are transmissible by the aerosol route, particular attention is given to air movement in these labs. Air moves from areas of lesser contamination to areas of higher contamination, such as from the corridor into the laboratory. Air movement is also single pass; exhaust air is not recirculated to other rooms.

All work that may create aerosols or splatter is done inside a biological safety cabinet. Wall, ceiling and floor penetrations are sealed to keep aerosols in and to keep gaseous decontaminants in.  Centrifuge tubes are placed into containment cups or heads in the biological safety cabinet (BSC), transferred to the centrifuge, spun, then returned to the BSC to be unloaded. In some laboratories the centrifuges themselves are enclosed in a vented area to minimize possible aerosol exposures created in the event of a centrifuge failure. Vacuum lines are protected with HEPA filters so that maintenance personnel are not exposed to infectious aerosols.

Depending on the nature of the work being done in the BSL-3 laboratory, additional personnel protective devices may be worn, such as respirators . When pulmonary protection is required, the laboratorians need to have appropriate medical evaluations and be trained in proper fit testing and care of their respirators.

Supervisors of BSL-3 laboratories should be competent scientists experienced in working with the agents. They establish criteria for entry into the laboratory, restrict access, develop appropriate practices and procedures, and train the laboratorians. They are also responsible for developing the laboratory safety manual. The lab personnel must rigorously follow the established guidelines, demonstrate proficiency in performing their various procedures, and receive appropriate training. They must participate in specified medical surveillance programs, and report all incidents that constitute potential exposures.


"The 1, 2, 3's of Biosafety Levels", Jonathan Y. Richmond, Ph.D., Director, Office of Health and Safety Centers for Disease Control and Prevention Atlanta, GA 30333, adapted from the CDC/NIH 3rd edition of Biosafety in Microbiological and Biomedical Laboratories

"CDC to mix avian, human flu viruses in pandemic study", Robert Roos, Center for Infectious Disease Research&Policy Academic Health Center -- University of Minnesota