A biocontainment patient-care unit (BPCU) is a facility designed and operated to maximize patient care with appropriate infection-control practices and procedures. A BPCU is secure, is physically separated from other patient-care areas, and has special air-handling systems.1

The National Institutes of Health's new Special Clinical Studies Unit (SCSU) in Bethesda, Md., is a highly specialized BPCU, housing patients with extremely infectious diseases transmissible by respiratory aerosolization, direct contact with primary body fluids, or dried infectious particles from body fluids. The SCSU has three patient rooms plus an occupational-exposure isolation room (OEIR). It is equipped to meet all clinical-care needs, including basic medical observation, minor surgical procedures, and intensive care. Thus, planning had to address housekeeping, security, emergency evacuation, and the use of experimental therapeutics.

This article will discuss design criteria used for the SCSU, which can be applied for any other type of airborne-infection-isolation suite (AIIS).

General Design Features

The SCSU receives air via the main clinical supply-air system, which is served by air-handling units located in another part of the building. This is a manifolded system providing supply air to all patient rooms and support spaces (Figure 1).

All clinical spaces are served by a non-recirculating (100-percent exhaust) HVAC system. All general clinical spaces, as well as the adjacent Vaccine Evaluation Clinic (VEC), are served by general exhaust systems consisting of multiple exhaust fans connected to a common exhaust-air manifold. Dedicated isolation-room exhaust systems consist of multiple exhaust fans connected to a common exhaust-air manifold. If one fan fails, the remaining fans compensate to provide the required design exhaust-air quantity.

The VEC is exhausted through the general clinical exhaust system, while the SCSU is exhausted through a dedicated system. Exhaust air from all SCSU spaces, including the OEIR, is manifolded in the dedicated exhaust system.

The dedicated system is equipped with high-efficiency-particulate-air (HEPA) filters prior to exhaust fans and discharges outside (Figure 2).

At both entrances to the SCSU are vestibules maintained at negative pressure relative to the adjoining corridors. The OEIR has an anteroom maintained at negative pressure relative to the rest of the SCSU to mitigate the risk of release of an airborne agent. The negative pressure of the patient rooms, the OEIR, and the SCSU is monitored and alarmed at the nurses' station.