6 Several environmental pathogens have life-cycle forms that are similar in size to droplet nuclei and may exhibit similar behavior in the air. 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). 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).

remain suspended indefinitely in air, and.

be protected by a coat of dry secretions,.

contain potentially viable microorganisms,.

34 Droplet nuclei are the residuals of droplets that, when suspended in air, subsequently dry and produce particles ranging in size from 1–5 μm. The spread of airborne infectious diseases via droplet nuclei is a form of indirect transmission. Strategies to control the spread of these diseases are outlined in another guideline. 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. 6 Examples of pathogens spread in this manner are influenza virus, rhinoviruses, adenoviruses, and respiratory syncytial virus (RSV). 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. Exposure to microorganisms in droplets (e.g., through aerosolized oral and nasal secretions from infected patients 33 ) constitutes a form of direct contact transmission. Respiratory infections can be acquired from exposure to pathogens contained either in droplets or droplet nuclei. 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. Modes of Transmission of Airborne DiseasesĪ 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. Summary of ventilation specifications in selected areasġ. Strategy for managing TB patients and preventing airborne transmission in operating room Example of AII room with anteroom and neutral anteroom Example of negative-pressure room control for AII Example of positive-pressure room control for protection from airborne environmental microbes

Environmental Infection-Control Measures for Special Settings.

Infection-control measures for internal construction Construction/repair projects that require barrier structures

Internal Demolition, Construction, Renovations, and Repairs.

Strategies to reduce dust and moisture intrusion during external demolition and construction Unresolved issues associated with microbiologic air sampling Construction design and function considerations for environmental infection control Suggested members and functions of a multi-disciplinary coordination team for construction Ventilation hazards that may be associated with increased potential of airborne disease transmission

Construction, Renovation, Remediation, Repair, and Demolition.Infection Control Impact of HVAC System Maintenance and Repair.Engineered specifications for positive- and negative pressure rooms Heating, Ventilation, and Air Conditioning Systems.Microorganisms associated with airborne transmission

Clinical and epidemiologic characteristics of TB Tuberculosis and Other Bacterial Diseases.Clinical and epidemiologic characteristics of aspergillosis Aspergillosis and Other Fungal Diseases.Modes of Transmission of Airborne Diseases.

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