Estimates of Improved Productivity and Health from Better Indoor Environments

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Hand-to-hand transmission of rhinovirus colds.

J Hendley, Chad J Gwaltney, P B Moskalski (1978)

Rhinovirus was transmitted from experimentally infected volunteers (donors) to susceptible recipients and the efficiencies of spread by hand-to-hand contact and large- and small-particle aerosols compared. Transmission of infection was very efficient by the hand route: 11 of 15 hand-contact exposures initiated infection, compared with one of 12 large-particle (P less than 0.005) and none of 10 small-particle (P less than 0.005) exposures. Rhinovirus was present in nine of 18 (50%) nasal swab specimens, 28 of 43 (65%) hand rinses, and seven of 18 (39%) saliva specimens of donors; geometric mean titers of positive specimens were 10(1.5), 10(1.4), and 10(1.2) tissue culture infectious dose 50/ml (TCID 50/ml), respectively. Rhinovirus was present in 20 of 43 (46%) recipient hand rinses, with a geometric mean titer of 10(1.4)TCID50/ml. Virus on donors' hands was transferred to recipients' fingers during 20 of 28 (71%) 10-second hand-contact exposures. These findings support the concept that hand contact/self-inoculation may be an important natural route of rhinovirus transmission.

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Aerosol transmission of rhinovirus colds.

Nicole Jennings, C D Wartgow, Ivy E. Dick … (1987)

Rhinovirus infections may spread by aerosol, direct contact, or indirect contact involving environmental objects. We examined aerosol and indirect contact in transmission of rhinovirus type 16 colds between laboratory-infected men (donors) and susceptible men (recipients) who played cards together for 12 hr. In three experiments the infection rate of restrained recipients (10 [56%] of 18), who could not touch their faces and could only have been infected by aerosols, and that of unrestrained recipients (12[67%] of 18), who could have been infected by aerosol, by direct contact, or by indirect fomite contact, was not significantly different (chi 2 = 0.468, P = .494). In a fourth experiment, transmission via fomites heavily used for 12 hr by eight donors was the only possible route of spread, and no transmissions occurred among 12 recipients (P less than .001 by two-tailed Fisher's exact test). These results suggest that contrary to current opinion, rhinovirus transmission, at least in adults, occurs chiefly by the aerosol route.

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Airborne infection. Theoretical limits of protection achievable by building ventilation.

E. Nardell, Jorn Cheney, Sue C Etkind … (1991)

Of 67 office workers 27 (40%) had documented tuberculin skin test conversions after an estimated 4-wk exposure to a coworker with cavitary tuberculosis. Worker complaints for more than 2 yr before the tuberculosis exposure prompted investigations of air quality in the building before and after the tuberculosis exposure. Carbon dioxide concentrations in many parts of the building were found to be above recommended levels, indicating suboptimal ventilation with outdoor air. We applied a mathematical model of airborne transmission to the data to assess the role of building ventilation and other transmission factors. We estimated that ventilation with outside air averaged about 15 feet 3/min (cfm) per occupant, the low end of acceptable ventilation, corresponding to CO2 levels of about 1,000 ppm. The model predicted that at 25 cfm per person 18 workers would have been infected (a 33% reduction) and at 35 cfm, a level considered optimal for comfort, that 13 workers would have been infected (an additional 19% reduction). Further increases in outdoor air ventilation would be impractical and would have resulted in progressively smaller increments in protection. According to the model, the index case added approximately 13 infectious doses (quanta) per hour (qph) to the office air during the exposure period, 10 times the average infectiousness reported in a large series of tuberculosis cases. Further modeling predicted that as infectiousness rises, ventilation would offer progressively less protection. We conclude that outdoor air ventilation that is inadequate for comfort may contribute to airborne infection but that the protection afforded to building occupants by ventilation above comfort levels may be inherently limited, especially when the level of exposure to infection is high.