In a study conducted in a Swiss textile mill, negative ionizers were placed in two, 60’ by 60’ rooms, each containing 22 employees. In one room, the negative ion electronic air cleaner was turned on during the course of the study. In the other room, the negative ion air purifier was permanently turned off, although the employees in this room were led to believe they were working in a room enriched by negative ions. During this six-month study, a total of 22 sick days were lost by employees working in the room in which the negative ionizer was operating. In the room where the machine was not operating, a total of 64 days were lost to sickness. During a month-long flu epidemic, the first group lost a total of 3 days to sickness, while the second group lost a total of 40 days to sickness (Stark, 1971).

In a test involving a Swiss bank office, one group of 309 worked in a negative ion-treated environment. A second group of 362 worked in an untreated environment. Over the next several months, for every day lost to respiratory illness (cold, flu, laryngitis, etc.) in group one, 16 days were lost to respiratory illness in group two (Soyka, 1991).

In a Surrey University study at the Norwich Union Insurance Group headquarters, eight negative ion generators were placed in the computer and data preparation section. Before the test, the research team spent a month compiling incident rates for complaints of sickness and headaches. During the test in which the negative ion air purification systems were in operation, incidents of sickness and headaches were reduced by 78%. After testing was completed, the Norwich Union opted to keep the negative ion electronic air cleaners (Soyka, 1991).