HVAC officemate.

Heating, ventilation, and air-conditioning (HVAC) systems, particularly those in humid climates, frequently harbor microbial growth that may contribute to illness among workers. Researchers are on the lookout for technologies that can kill pathogens before they circulate throughout a work space. One such technology, ultraviolet germicidal irradiation (UVGI), has long been used to inactivate microbial aerosols, mostly in the occupied spaces of medical facilities. A study published in the 29 November 2003 Lancet suggests that UVGI lights installed in office HVAC systems can effectively reduce microbial growth and improve worker health.

Dick Menzies, director of the Respiratory Epidemiology Unit at Canada's McGill University, led a team of researchers in a double-blind trial of 771 participants working in three Montreal office buildings. UVGI lights were installed in the buildings' HVAC systems to irradiate cooling coils, drip pans, and filters. The lights were turned on for 4 consecutive weeks, then off for the next 12 weeks several times over one year. Office workers reported at several points throughout the year whether they had any of 10 specific symptoms, including headache, nasal congestion, and irritation of the skin, eyes, and nose.

During the test period, the researchers measured airborne microbes and endotoxins within the HVAC systems, in the outdoor air, and at selected workstations. Following exposure to UVGI, median concentrations of viable microorganisms and endotoxins on HVAC surfaces were reduced by an overall average of 99%. With UVGI on, workers reported 30% fewer work-related mucosal symptoms, 40% fewer respiratory symptoms, and 20% fewer symptoms overall than with UVGI off.

The authors believe UVGI lamps could be installed in most existing office buildings and, based on the incidence of building-related illnesses among U.S. workers, could resolve work-related symptoms due to HVAC microbial contamination in about 4 million people in the United States alone. They estimate the cost of installing these systems at approximately $52 per worker, with annual maintenance costs of approximately $14 per worker. A report in the September 2002 American Journal of Public Health estimates productivity losses among U.S. workers due to building-related illnesses at $20-70 billion annually, or $225-787 per worker.

While agreeing that UVGI can be effective in killing microbes, critics question the relevance of the study's conclusions for widespread application. Karin Foarde, director of the Microbiology Department at Research Triangle Institute in Research Triangle Park, North Carolina, who has extensively studied the effectiveness of UVGI, notes, "The buildings had such low levels of contamination to begin with, I have concerns about the strength of the authors' conclusions on surface and airborne reductions." She adds, "It would be interesting to know how UVGI would perform in a humid climate like the Southeast with higher levels of contamination."