Contamination Control in “The Hot Zone”
By Susan English
Fort Detrick, MD– “Reston,” “Sudan,” “Zaire”–are names which, with the possible exception of the first, suggest exotic vacation destinations for the jaded traveler. Actually, however, they are deadly strains of the Ebola virus, three of the more than 20 Biosafety Level 4 viruses handled by scientists at the U.S. Army`s Medical Research Institute of Infectious Diseases (USAMRIID; Fort Detrick, MD). Recent interest in the Institute and its work was triggered by the bestselling book “The Hot Zone,” in which author Richard Preston recounts in frightening detail a real virus scare–a particularly virulent African virus known as “Ebola”– in Reston, VA in 1989.
Although the Ebola virus did not turn out to be fatal to humans, the movie industry, undeterred by facts, quickly followed up with a movie called “Outbreak.” The movie features the Institute in a disastrous but highly fictionalized situation. Institute spokeswoman and biomedical writer Cheryl Parrott confirmed in a USA Today article (Feb. 25) that nothing even remotely resembling the movie`s plot has happened during the 25 years of the Institute`s existence. Nevertheless, the procedures for contamination-control highlighted by the media blitz are critically important not only because the stakes are so high–regional, if not global dispersion–but also, because of the deadly nature of the “contaminants.” “Personnel, as well as products, must be protected,” says Dr. Robert Hawley of the Institute`s Safety Office.
Levels of containment, or contamination control, at the institute range from Biosafety Levels 1 to 4. Biosafety Level 1 is the least hazardous, while Level 4 deals with the highest hazard agents. Levels 1 and 2 include those organisms generally found in the normal environment causing diseases such as salmonellosis, hepatitis, or even the common cold. Biosafety Level 3 encompasses moderately hazardous agents usually found in tropical regions outside the United States, such as Africa`s Rift Valley fever virus. Biosafety Level 4 includes “high hazard” or exotic agents, also not indigenous to this country, such as the Ebola strains.
According to Dr. Hawley, protection of laboratory workers starts with engineering controls. Although the Institute does not refer to them as “cleanrooms,” its laboratories, ranging in size from 2,600 ft.2 to 26,000 ft.3, have 10-12 air changes per hour, which is roughly equivalent to a Class 10 cleanroom. Within the Institute`s laboratories, all supply air is 65 percent filtered, and exhaust air is also passed through a HEPA filter. At lower levels of containment, workers are required to make a complete change of clothing before they enter the laboratory and to wear “surgical scrubs.”
The Institute`s primary barrier tools are HEPA-filtered and exhausted workstations or “biological safety cabinets,” many of which are manufactured by Baker Company Laboratories (Sanford, ME). The National Sanitation Foundation categorizes them as Class I, Class II-Types A, B, B2, B3, and Class III. Class I and II biological safety cabinets are used for low risk and moderate risk biological agents; Class III, for higher risk agents.
Environmental protection is dealt with not only through HEPA filtration of the exhaust air, but also by steam sterilization. In fact, everything coming out of the lab is sterilized, and all liquids are either disinfected in place with agents such as bleaches or are run through a steam sterilization process similar to an autoclave. Although no infectious waste is involved at this stage, after being hosed down, floor drains carry all effluent down to a sterilizing tank, so that even wash water is sterilized before discharge.
Despite Hollywood`s portrayal to the contrary, nothing at the facility can be considered “classified,” according to Dr. Hawley. Indeed, any veil of secrecy, if there was one, was rudely ripped away by Richard Preston`s book, not to mention the Institute`s starring role in the movie and the ensuing publicity it generated. n