Human cases have been confirmed, but currently the virus has not mutated to a state of transmissibility from human to human. So far it has traveled from Asia to parts of Europe. Some health experts have predicted that it is only a matter of time until the virus is capable of spreading through person-to-person contact.

Isolation Strategies

It might be useful to think in terms of indoor air quality (IAQ) strategies in general. The best way to prevent contamination is by not allowing the contaminants into the building (as in the case of tobacco smoke), or by filtering them out. When hospital administrators look at minimizing the spread of disease, one of the first strategies they look at is the isolation of infected populations.

"The issue here is isolation," Hermans said. "Hospital operators can prepare now, and already have been in some cases, for mass casualties and airborne transmissions. How you go about that depends on where you are and what your numbers could be."

Health care facilities in rural areas are not exempt from dealing with high numbers of infectious patients, he pointed out.

"Urban hospitals, under extraordinary circumstances, may need to move people out to the rural communities," he said.

Hermans is chairing a committee writing proposed Standard 170P, "Ventilation of Health Care Facilities." The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and the American Society for Healthcare Engineering (ASHE) are developing the standard.

"People are making different preparations," he said, depending on their population density and demographics. Some communities are planning isolation areas that actually are offsite of the hospital itself, in case of mass casualties and airborne transmissions.

"Here in Minneapolis it could be someplace like the convention center," Hermans said. "It's very difficult to isolate large numbers of infectious people from everybody else."

Steps To Take

The first thing mechanical systems operators will want to do, he said, is make sure their hospitals' existing isolation rooms' ventilation systems work effectively.

He recommended that they perform testing using in-house staff or an outside testing company, possibly in conjunction with system recommissioning.

Such spaces need separate ventilation systems that do not mix airstreams with ventilation from other areas of the hospital. Air needs to be exhausted outdoors, but may require some filtration. They also need to be pressurized appropriately to protect both the patient in isolation and the rest of the hospital's staff and patients.

"Pressurization is checked whenever an infectious patient enters isolation," said Hermans, who has done work on tuberculosis (TB) isolation systems.

"Any hospital with TB patients will have isolation rooms," he continued. "A newer hospital will have an isolated ventilation system in the ER if nothing else."

Mechanical systems maintenance should be focused on containment, "on HVAC exhaust systems more than anything else," he said. Exhaust systems need to be inspected to ensure that they are functioning properly; this includes fans and connecting ductwork, Hermans said. "Seal up the room envelope, the windows, and doors. Get 'em as tight as possible."

Of course, the system must provide heating and cooling as appropriate for the patients and staff based on weather conditions. You would think it would be a given. However, "in extraordinary events, sometimes priorities shift," Hermans said. "The normal rules of how you handle infection changes." In short, don't take heating and cooling for granted.

According to Standard 170P, ventilation for airborne infection isolation rooms must meet the following requirements:

Provide a continuous differential air pressure monitor that alerts staff when the space's differential pressure is not maintained. ("Things like flutter strips and smoke trails would be fine," Hermans said. Flutter strips may be more practical than smoke trails for long-term monitoring, he added. "The point is, you don't have to get too expensive with this.")

All air from airborne infection isolation rooms must be exhausted directly outside.

All exhaust air from airborne infection isolation rooms, associated anterooms, and associated toilet rooms, must not be combined with any nonisolation exhaust system.

Exhaust grilles or registers in the patient room must be located directly above the patient bed on the ceiling, or on the wall near the head of the bed.

The reverse of the isolation room is the patient protective environment room; this patient room is intended to protect an immunocompromised patient from human and environmental airborne pathogens. Ventilation for these rooms would require:

A room envelope that is well sealed.

A continuous differential air pressure monitor that alerts clinical staff when differential pressure is not maintained.

Supply air diffusers above the patient bed.

Return/exhaust grilles or registers located near the patient room door.

Importance Of Ventilation

Controlled ventilation plays a key role in preventing cross contamination, whether it is from a biological agent such as a virus or a chemical agent released in a spill, he said. Requirements to ensure appropriate ventilation can be found in Standard 170P.

"Without high-quality ventilation, patients, health care workers, and visitors can become infected through normal respiration of particles in the air," said Hermans. These are called nosocomial infections.

"Poorly ventilated health care facilities are places where the likelihood of pathogenic particles occurring in the air is quite high. Because such pathogens can be found everywhere in health care facilities, and because patients are susceptible to them, additional care should be taken in the design of ventilation systems."

The proposed standard defines requirements for ventilation system design intended to provide environmental control for comfort, as well as infection and odor control.

It addresses systems, equipment, space ventilation for a variety of areas in health care facilities (including airborne infection isolation rooms, critical care units, burn units, surgery rooms, and Class B and C operating rooms), plus planning, construction, and system startup.

The standard also considers "chemical, physical, and biological contaminants that can affect the delivery of medical care to patients, the convalescence of patients, and the safety of health care workers and visitors." Its review period has just ended.

Hermans would like to see plenty of comments from hospital engineers. "The standard is intended for design engineers, but it needs to be practical and useful. For instance, think about what you're going to do when a whole bunch of infectious people come in. That's tough.

"There are a lot of clever ideas out there," he continued. "It's a great thing that people are out there sharing ideas. The more we talk, the better prepared we can be."

Publication date: 11/07/2005