| Isolation facilities for infection control in Hong Kong hospitals were put under the spotlight after the outbreak of severe acute respiratory syndrome (SARS) in 2002-2003. Hospital design in Hong Kong normally allows 5 percent to 6 percent of the space for infection isolation, but some hospitals, especially the older ones, may not meet these requirements.
Major concerns included the adequacy of infectious disease wards and wash-up and gown/ de-gown facilities, standards of air conditioning systems, and the effectiveness of space pressure control, etc. In light of these deficiencies and concerns, the need for upgrading infection-isolation facilities is paramount. Hong Kong’s Hospital Authority has plans to upgrade existing hospitals to international standards and in the long-term to build an infectious-disease hospital. Renovation works in nine hospitals were nearly completed at the time of writing and will provide more than 1200 beds for infectious disease patients if the next possible wave of SARS occurs, as is predicted by medical experts.
Isolation Rooms and Biosafety Level-3 Laboratories
Laboratory safety related to infection control measures also became a concern after technicians in Singapore and Taiwan who handled SARS specimen became infected with the disease. Now, according to World Health Organization guidelines, only laboratories with rating of biosafety level-3 or higher are safe for handling the SARS virus. The World Heath Organization’s levels of safety for laboratory design are: 1- basic, 2 - basic with additional limitations for access and personnel, 3 - containment, and 4 - maximum containment.
A biosafety level-3 laboratory is for work involving microorganisms that usually cause serious human or animal disease but for which effective treatment and preventive measures are available. The design of a biosafety level-3 laboratory is similar to that of an isolation room. Both demand an environment that is safe for workers handling objects containing airborne infectious diseases and that prevents the spread of diseases to the outside. Both demand chemical-resistant and cleanable wall/floor surfaces and anteroom, negative space pressure control, etc.
From our design experience of several new hospitals and three accredited level-3 laboratories (under Australian Standards) in the Medical Complex of the University of Hong Kong, we have formulated a set of practical design guidelines aimed at achieving a workable, safe, yet cost-effective solution for isolation rooms. The recommendations described in this article were derived from local/international research studies, fundamental engineering concepts, local/international healthcare institutes’ recommendation and our design experience in regard to Hong Kong hospitals and biosafety level-3 laboratories. Our findings in the key issues of room planning, containment control, space pressure control, airflow control and system performance monitoring are presented below.
Room Planning
As in most guidelines, we recommend the provision of an anteroom (Figure 1 on the following page), which serves as a barrier between the isolation room and outside corridor and:
- Is used by health-care workers to scrub and gown/de-gown
- Provides for storage of clean/soiled materials
- Cushions the impacts of opening doors and traffic.
Figure 1: Layout planning of infection Isolcation room. |
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A typical isolation suite includes a bathroom for patient use. Wash-hand basins are needed inside the isolation room and anteroom for healthcare workers. These should preferably be automatically operated to avoid contact infection. The inner surfaces of each room in the isolation suite should be smooth, chemical-resistant and easy to clean. Typical finishing materials are vinyl sheet flooring, special coating on dry/masonry partition, and metal ceiling or plasterboard ceiling with special coating.
Containment Control
Despite it not being emphasized in current isolation room design guidelines, a sealed room construction as mandatory for biosafety level-3 laboratory is equally crucial to an isolation room in its effectiveness to curb the spread of disease. The “sealed box” concept will correctly maintain the precise and stable control of space pressure relationships among each member room and outside corridor, making it a prerequisite of a sound design for isolation suites.
The key is whether the prescribed pressure differentials can be established at the minimum required air volumes supplied to and exhausted from the member rooms in a cost-effective manner. From surveys, we identified common problems of being unable to precisely maintain the target pressure differentials due primarily to the absence of a sealed envelop. In some cases, the pressure differentials were ac hieved but at the expense of unnecessarily large air volumes operated by over-sized central air handlers. From design experience in biosafety level-3 laboratories, achieving a well sealed room simply demands good coordination in construction details.
Tests should be performed to ensure the room air tightness before operation. Key design issues suggested for isolation rooms (and not discussed elsewhere in this article are:
- Structural soffit should be used as the airtight barrier surface.
- Door should be proprietary-sealed type and self closing.
- Windows should be sealed and junction of the window mullion to the wall be engineered.
- Services penetration should be airtight and well coordinated with the wall/slab construction method.
- Special attention should be paid to services outlets, such as sockets, lighting switches, thermostats and data outlets.
- No floor drains should be considered inside the isolation room and anteroom.
- Access panels should be minimized. If unavoidable, an airtight access panel should be adopted.
Pressure Control and Airflow Distribution
Constant offset between the supply and exhaust air volumes should be controlled continuously to quantitatively maintain the space pressure and pressure relationship between each member room. The amount of the offset is a function of the as-fitted room leakage area and the target pressure differential. The final exact figure of offset is ascertained during testing and the commissioning stage.
Constant space pressure control will establish a series of desirable airflow patterns; for instance, air flows from the cleaner area towards the dirtier area. The airflow direction for an isolation room should be from the outside corridor via the anteroom into the isolation room, which is the most negative pressure zone.
The anteroom doors should be interlocked such that both doors cannot be opened simultaneously to help to maintain the negative space pressure condition inside the isolation room during healthcare worker circulation or patient transportation.
System Performance and Monitoring
The system operation status should be continuously monitored and alarms generated when system fails, the air pressure differential between the isolation room and adjacent anteroom or corridor is not maintained, or there is an airflow failure. Monitoring panels should be located in front of the anteroom and at the nurse station. The pressure failure alarm should also be interlocked with the door open status such that a nuisance alarm is prevented during normal health-care worker/patient transient traffic.
Testing and Commissioning, Operation and Maintenance
The performance of an isolation room relies not only on the design accuracy, but also on the installation coordination and testing and commissioning, all of which should be documented.
Given its usefulness for the biosafety level-3 laboratory, a validation process is also suggested for the isolation room. The validation should be executed by an independent reviewer who pursues design checking, installation inspection and final performance testing of the isolation room to certify the system is operated as designed. Finally, a proper operating and maintenance schedule of the system is essential.
Medical Surveillance Policy
Successful operation of an infection isolation suite relies not only on the correct design, but also on a medical surveillance policy, which relates mainly to the staff training, infection control procedures enforcement, risk assessment, disinfection procedures, preventive maintenance policy, operation procedures, and periodic checking of the system and equipment performance. Early involvement of hospital’s infection control committee during design stage will help to precisely identify the design requirements relating to infection control objectives.
Conclusion
By reviewing the current design guidelines of isolation suites and biosafety level-3 laboratories and from our design experience, we derived a number of design analogies that formed a set of practical design guidelines we recommended for isolation suites. The key design issues include the significance of sealed construction, space pressure and airflow control, air distribution and quality system monitoring, testing and commissioning, and operation and maintenance. Each of the above aspects must be engineered before an infection isolation suite can meet its functional objectives in a cost-effective manner.
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