Personal air cleaners add to TB protection

Hospitals are discovering a relatively inexpensive device that can help reduce the risk of occupational exposure to tuberculosis: the portable room air cleaner.

While small air cleaners are no substitute for proper ventilation systems and negative-pressure rooms, they afford some extra protection for health care workers, says Paul Jensen, PhD, chief of the Laboratory Research Branch in the Division of Respiratory Disease Studies at the National Institute for Occupational Safety and Health (NIOSH) in Morgantown, WV. "There are a number of hospitals which may meet the six-air-changes-per-hour guideline for existing facilities but would like to provide an additional level of protection for staff. In some cases, they’ll use portable room air cleaners. There are many companies that sell a fan and filter in a box," he says. "The idea is that you’ll pull air from the room, send it through a filter, and the filter will remove bioaerosol organisms in the air. Depending on the flow rate of the unit, it could add anywhere from less than one to several additional air changes per hour."

Proper placement is crucial to the effectiveness of these air cleaners, notes Jensen. For example, if it’s too close to the room’s supply air vent, you may simply be cleaning clean air. "The best thing to do would be to have your facilities engineer assist in sizing the units [for adequate flow rate] and placing the unit so it will work in unity with existing ventilation system," he says.

In the "hierarchy" of controls — measures that provide protection to workers — administrative controls (such as TB policies and procedures) come first. Then engineering controls take precedence over personal protective equipment such as respirators. That doesn’t mean that respirators aren’t necessary or important, but that hospitals should do all they can to protect staff through minimizing exposure through administrative controls and through proper ventilation, says Jensen. "One of the easiest things to do is to ventilate," he says. "Every hospital does have some ventilation. It’s just a matter of how that system interacts with the rest of the hospital."

Unfortunately, sometimes ventilation systems are inadequate. In health hazard evaluations in the 1990s, NIOSH investigators found ventilation systems at hospitals that allowed air from "isolation" rooms to leak into corridors or even into other units of the hospital.

"[At one hospital], there was a general flow of air out of the infectious disease ward and into the core area. In fact, the air flowed through the core area and into an adjacent wing of the hospital. This condition could cause the circulation of infectious agents to other wards and floors of the hospital because of shared heating, ventilating, and air conditioning [HVAC] systems," the investigators’ report stated. Here are some tips, based on the health hazard reviews and Centers for Disease Control and Prevention guidelines:

• Base your ventilation system design on a TB risk assessment, including the number of patients seen in your hospital and the incidence in the community. While all systems should meet minimum standards, higher-risk facilities may use more frequent air changes, HEPA filters, and upper-air room irradiation (UVGI lamps) to further reduce infectious droplets.

• Take advantage of a hospital renovation to update and improve your ventilation system to a minimum flow rate of 12 air changes per hour.

• CDC guidelines call for a minimum of six air changes per hour for existing facilities, and both CDC and the American Institute of Architects (AIA) recommend 12 air changes per hour for new or renovated facilities.

• Test your isolation room daily with smoke tubes to make sure the air is flowing from the hallway, under the door, and into the room. Air should not flow in the reverse direction.

• Make sure the air is exhausted directly outdoors and not near an intake.

• If some air must be recirculated through the hospital’s main HVAC system, use HEPA filters to remove organisms.

[Editor’s note: See the Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Facilities, 1994. MMWR 1994; 43(RR13):1-132. Or go to the CDC web site: The American Institute of Architects’ Guidelines for Design and Construction of Hospital and Health Care Facilities, 2001 Edition, are available from the AIA, 1735 New York Ave. N.W., Washington, DC 20006-5292. Telephone: (800) 242-3837. Web:]