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发表于 2009-6-24 23:03
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国内最新版的教科书都是这么描述的，空气传播包括了经飞沫、飞沫核（气溶胶）和尘埃传播，确实与胡教授的理念有所不同啊！尤其是对飞沫、飞沫核、气溶胶等确实需要按微粒的大小和在空气中沉降的速度来区分。
潮水 发表于 2009-6-24 22:23
说明我们很多专家包括CDC的权威专家，对这个概念没有完全弄清楚。
2003年，美国CDC发布的《Guidelines for Environmental Infection Control in Health-Care Facilities》
对空气传播的疾病有明确的描述。
C. Air
1. Modes of Transmission of Airborne Diseases
A variety of airborne infections in susceptible hosts can result from exposures to clinically significant
microorganisms released into the air when environmental reservoirs (i.e., soil, water, dust, and decaying
organic matter) are disturbed. Once these materials are brought indoors into a health-care facility by
any of a number of vehicles (e.g., people, air currents, water, construction materials, and equipment),
the attendant microorganisms can proliferate in various indoor ecological niches and, if subsequently
disbursed into the air, serve as a source for airborne health-care–associated infections.
Respiratory infections can be acquired from exposure to pathogens contained either in droplets or
droplet nuclei. Exposure to microorganisms in droplets (e.g., through aerosolized oral and nasal
secretions from infected patients33) constitutes a form of direct contact transmission. When droplets are
produced during a sneeze or cough, a cloud of infectious particles >5 μm in size is expelled, resulting in
the potential exposure of susceptible persons within 3 feet of the source person.6 Examples of
pathogens spread in this manner are influenza virus, rhinoviruses, adenoviruses, and respiratory
syncytial virus (RSV). Because these agents primarily are transmitted directly and because the droplets
tend to fall out of the air quickly, measures to control air flow in a health-care facility (e.g., use of
negative pressure rooms) generally are not indicated for preventing the spread of diseases caused by
these agents. Strategies to control the spread of these diseases are outlined in another guideline.3
The spread of airborne infectious diseases via droplet nuclei is a form of indirect transmission.34
Droplet nuclei are the residuals of droplets that, when suspended in air, subsequently dry and produce
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particles ranging in size from 1–5 μm. These particles can a) contain potentially viable microorganisms,
b) be protected by a coat of dry secretions, c) remain suspended indefinitely in air, and d) be transported
over long distances. The microorganisms in droplet nuclei persist in favorable conditions (e.g., a dry,
cool atmosphere with little or no direct exposure to sunlight or other sources of radiation). Pathogenic
microorganisms that can be spread via droplet nuclei include Mycobacterium tuberculosis, VZV,
measles virus (i.e., rubeola), and smallpox virus (i.e., variola major).6 Several environmental pathogens
have life-cycle forms that are similar in size to droplet nuclei and may exhibit similar behavior in the
air. The spores of Aspergillus fumigatus have a diameter of 2–3.5 μm, with a settling velocity estimated
at 0.03 cm/second (or about 1 meter/hour) in still air. With this enhanced buoyancy, the spores, which
resist desiccation, can remain airborne indefinitely in air currents and travel far from their source.35 |
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发表于 2009-6-23 10:16
发表于 2009-6-24 11:33
发表于 2009-6-24 13:25
