When people cough and sneeze, they can expel bacteria and viruses into the indoor air. For some types of common respiratory illnesses, inhalation of these bacteria or viruses can lead to infection and illness. These illnesses may also be transmitted by direct person-to-person contacts and other means. In theory, increased ventilation can reduce respiratory illness rates by lowering the indoor air concentrations of these bacteria and viruses, and thereby decrease sickness absence rates (see next section).
Three studies of ventilation and respiratory illness (one performed in military barracks, one in a jail, and one in a nursing home) found an increase in respiratory illness with very low ventilation rates compared to substantially higher ventilation rates (2.5 versus 20 cfm per person, 8 versus 26 cfm per person, 4 versus 8 cfm per person ). In these studies [25-27], the percentage increase in respiratory illness in buildings or spaces with the lower, compared to higher, ventilation rates ranged from approximately 50% to 370%. Similar results might be expected in other high density buildings such as school classrooms, though no data are available. However, it is not clear that effects of ventilation rate on respiratory illness would be comparable in more typical buildings with lower occupant density.
In a recent literature review performed by a multidisciplinary panel , a broader set of evidence was considered to evaluate the role of both ventilation rates and indoor airflow patterns in respiratory disease. The review panel concluded that "there is strong and sufficient evidence" to demonstrate that lower ventilation rates and indoor airflow from infected to uninfected people are associated with increased transmission of infectious diseases "such as measles, tuberculosis, chickenpox, influenza, smallpox and SARS". Based on the literature reviewed, the panel stated "This evidence supports the use of negatively pressurized isolation rooms for patients with these diseases in hospitals.....". However, the panel also concluded that the available data were insufficient to form a basis for specifying the minimum ventilation rates needed to limit infectious disease transmission in various types of buildings.