Daily testing ordered for TB isolation rooms
Monitoring devices fail to function properly
Officials in New York State are going low-tech to test airflow in hospital tuberculosis isolation rooms as a result of recent evaluations revealing high rates of faulty airflow that could have infected both health care workers and patients.
TB investigations conducted by the New York State Department of Health (NYSDOH) between 1992 and 1998 found that 38% of 140 respiratory isolation rooms evaluated had positive airflow relative to adjacent areas. In addition, rooms with electronic continuous airflow monitors failed to indicate actual airflow direction 50% of the time.
Those findings have prompted NYSDOH to require hospitals to test isolation rooms daily with smoke tubes that release visible smoke. Movement of the smoke within the room indicates airflow direction, and it’s easy to see if smoke is escaping into hallways under or around doors. All isolation rooms that are occupied by a potentially infectious TB case must be smoke-tested, regardless of the use of continuous electronic monitors, according to the directive issued to hospital administrators throughout the state.
If only one or two isolation rooms had airflow problems, they would have been considered an exception, but because problems "did not seem to be uncommon, that’s why we wanted to alert hospitals that these relatively new monitoring systems may still need further exploration," Margaret J. Oxtoby, MD, director of the NYSDOH’s Bureau of Tuberculosis Control, tells Hospital Employee Health.
Smoke-tube testing is not done routinely on a daily basis, Oxtoby says, but "given the expense and massive engineering efforts that have gone into developing these isolation rooms throughout the state, it’s also important to do standard low-tech monitoring. We just shouldn’t spend all our money, create these rooms, and feel like we’re home free."
HCWs at low risk for exposure
Oxtoby points out that no HCWs were found to have been exposed to infectious TB due to faulty airflow.
"Overall, the big picture here is that health care workers appear to be at relatively low risk for exposure on the job," she says. "When we have health care worker cases reported, we go back very carefully to sort out where they might have had exposure, and most of them have been documented to have been infected when they started employment, often coming from other countries where TB is much more prevalent than it is in the United States. The [occupational] risk is really related to the undiagnosed person who’s coughing and hasn’t yet been suspected of having tuberculosis."
The risk to workers after a patient is suspected of having TB is minimal, she adds.
However, minimizing risk to HCWs and other patients depends upon well-functioning isolation rooms for suspected or confirmed infectious TB cases. The Centers for Disease Control and Prevention (CDC) issued guidelines in 1994 for preventing TB transmission in health care facilities. Until the U.S. Occupational Safety and Health Administration (OSHA) issues a final TB standard, the regulatory agency generally is enforcing the CDC’s recommendations for engineering controls. The guidelines specify the need for monitoring and controlling airflow patterns within isolation rooms as well as airflow direction throughout a facility. Isolation rooms must be maintained at negative air pressure relative to adjacent areas.1
Negative pressure in a room can be measured by using smoke tubes to observe airflow within or between areas, the guidelines state. The CDC also requires periodic checks to ensure negative pressure and proper operation of continuous monitoring devices.
Officials with the National Institute for Occupational Safety and Health (NIOSH), the worker safety arm of the CDC, note that the NYSDOH directive for daily smoke-tube testing is consistent with CDC guidelines, which state: "If smoke tubes or other visual checks are used, TB isolation rooms and treatment rooms should be checked frequently for negative pressure. . . . TB isolation rooms should be checked daily for negative pressure while being used for TB isolation. . . . If pressure-sensing devices are used, negative pressure should be verified at least once a month by using smoke tubes or taking pressure measurements."
NIOSH never has been notified of problems relating to faulty operation of airflow monitoring devices, says spokesman Fred Blosser.
The agency has not been asked to become involved in NYSDOH’s isolation room evaluations, but "we’re always concerned when problems or questions about the safety of workers are raised," Blosser states. "We’re looking at issues raised by the New York findings, but at this point we don’t have any determination of what, if anything, we need to do."
Oxtoby says the NYSDOH directive exceeds CDC recommendations.
"Even if you have electronic devices, it would be best to also do daily smoke-tube testing," she advises. "We tend to trust that any high-tech device with a readout will tell us the truth, when in fact sometimes a very simple manual measure is more reliable because we know exactly what it means. Sometimes readout devices may only partially reflect what is happening and can be falsely reassuring if one depends on them entirely."
In evaluating the 140 isolation rooms, NYSDOH used a commercially available smoke-tube kit to generate visible smoke around doors and observed the smoke’s movement at the bottom of doors and through spaces between doors and frames. Primary factors associated with outward (positive) pressure were identified as:
• ventilation systems not balanced, 54% of failed rooms;
• shared anterooms, 14% of failed rooms;
• turbulent airflow patterns, 11% of failed rooms;
• automated control system inaccuracies, 10% of failed rooms.
In 50% of isolation rooms equipped with continuous monitors, airflow direction revealed by the smoke test was the opposite of that indicated by the continuous monitoring device. The inability of monitors to qualitatively indicate actual airflow direction was associated with instrument limitations (74%) and device malfunction (26%). Those shortcomings were not associated with any particular manufacturer or technological design.
"The question of where the air flows is important," Oxtoby states. "The risk [to HCWs] is not as high as it was before a lot of attention was given to standards for operating isolation rooms. Workers who go into isolation rooms to work directly with patients are wearing masks, so their risk of breathing in TB from direct contact with the patient is still minimized as long as the airflow is adequate in the room. We’re basically talking about a low risk and minimizing it even further."
Reference
1. Centers for Disease Control and Prevention. Guidelines for preventing the transmission of Mycobacterium tuberculosis in health care facilities, 1994. MMWR 1994; 43(No. RR-13): 1-132.
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