Basic Documentation

Page 2 of 12 Siemens Industry, Inc.
Document No. 149-903
Preventing the Spread of Disease
in Healthcare Facilities
In the years leading up to 1985, the annual number
of new cases of Mycobacterium Tuberculosis (TB) in
the United States was continuously decreasing and
it was assumed, that for all practical purposes, this
disease could be considered eradicated in the U.S.
However, a reversal in this downward trend occurred
in 1985, and in the years that followed, new
infections were reported at an alarming rate.
In 1990, this resurgence in TB prompted the U.S.
Centers for Disease Control and Prevention (CDC)
1
to issue an initial set of guidelines intended to
prevent the transmission of TB in healthcare
facilities. In 1994, an enhanced set of guidelines
superseded the 1990 version and called for
increased room ventilation and additional
engineering controls on ventilation systems serving
TB isolation rooms. In 1996, the CDC also issued
guidelines on isolation precautions in hospitals.
More recently, the outbreak of Severe Acute
Respiratory Syndrome (SARS) in Asia and Canada,
and the potential for biological terrorism has
heightened the focus on ensuring that healthcare
facilities incorporate state-of-the-art ventilation
systems and associated engineering controls for
protecting both patient populations and those
responsible for providing medical treatment of those
infected with an airborne transmitted disease.
This technology report summarizes the requirements
and recommendations for the prevention of
transmission of an airborne transmitted disease in
healthcare facilities based on the current industry
guidelines listed in the following section, as well as
the experience of knowledgeable healthcare facility
designers.
Current Industry Guidelines
In 2004, the CDC drafted an updated version of its
1996 Guideline on Isolation Precautions in Hospitals
for public comment before official release. This draft
is entitled: Preventing Transmission of Infectious
Agents in Healthcare Settings.
In 2003, the CDC issued guidelines for reducing the
propagation of diseases in healthcare facilities
entitled: Guidelines for Environmental Infection
Control in Health-Care Facilities.
1. U.S. Department of Health and Human Services, Centers for
Disease Control and Prevention, Atlanta, GA 30333, Web
site: http://www.cdc.gov/
In 2001, the Canadian Standards Association
published CAN/CSA-Z317.2-01 entitled: Special
Requirements for Heating, Ventilation, and Air
Conditioning (HVAC) Systems in Health Care
Facilities.
In 2006, the AIA published an updated version of its
2001Edition: Guidelines for the Design and
Construction of Hospital and Health Care Facilities.
The requirements for Airborne Infection Isolation
Rooms appear in section (3.2.2 and 10.2.2.1),
Protective Environment Rooms are in section
(10.2.2.2) and ventilation is in (Table 2.1-2).
In 2008, the American Society of Refrigeration,
Heating and Air Conditioning Engineers (ASHRAE)
released for public review a Proposed New Standard
170, Ventilation of Health Care Facilities, Fourth
Public Review (March 2008).
Disease Transmission
Aerosols and Moisture Droplets, and Direct Contact
are the two major avenues that transmit disease-
carrying pathogens from an infection source to
another person.
Aerosols and Moisture Droplets
Aerosols are 10 microns or smaller in size and are
often between 1 and 5 microns. They’re not visible
and can float indefinitely on room air currents.
Moisture droplets are much larger than aerosols and
are usually visible. Both aerosols and droplets
containing infectious pathogens are generated when
an infected person coughs or sneezes and even
when the person speaks.
Although moisture droplets can transmit disease,
they are a lesser concern than aerosols because the
larger size of a droplet causes it to sink faster and
mostly affect an area within about three feet from the
patient. Aerosol transmission is the greatest concern
because normal room air movement can cause
aerosols containing infectious pathogens to travel
appreciable distances. In fact, most airborne disease
transmission is by aerosols containing bacterial
agents (rather than viral agents). The most common
diseases that are transmissible by aerosol and
droplet transmission include TB, Influenza, Bacterial
Pneumonia, SARS, Measles, and Smallpox.