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A regimented microbial sampling scheme and exposure model was utilized to assess patient health risk associated with microbial contamination in heating, ventilating, and air-conditioning (HVAC) systems in a a general hospital. The health risk rating (HRR) categorized risks associated with microbial contamination as high, medium, low, and de minimis. The HRR were determined with input from an interdisciplinary team of experts in the fields of medicine, infection control, environmental health, engineering, microbiology, biostatistics, risk analysis, and industrial hygiene. A high risk rating recommends immediate intervention and environmental control, a medium risk rating recommends remediation activities in a staged manner, and a low risk rating calls for cleaning and possible remediation of isolated areas of contamination. A de minimis rating signifiesno microbial contamination. The exposure model accounted for the toxicity and pathogenicity potential (TP) of biological contaminants and contaminated surface area within the HVAC systems. A literature review was conducted to identify the pathogenic/opportunistic and toxigenic characteristics of species of fungal and bacterial contamination identified within the HVAC systems. Scores were developed to quantify the TP of each organism and used in the calculation of health risk. The health risk exposure assessment utilized the formula Health Risk = (Exposure)(TP). Exposure scores were determined according to the presence of an exposure pathway, location of HVAC system service (noncritical, critical, or super-critical area), and the contaminated surface area within the HVAC systems. Mean composite scores were utilized to provide a single HRR for the space under the environmental control of each HVAC system. The exposure model presented the combined health risk by a single unit of measurement so that hospital administrators could utilize the HRR in their decision making processes. The HRR model can be modified for use in other institutional settings, such as schools, dependent-care facilities, and geriatric-care facilities.

IAQ 2007 Conference held in Baltimore, Maryland, October 14-17, 2007

Units: I-P