«Health and Productivity Gains from Better Indoor Environments and Their Implications for the U.S. Department of Energy William J. Fisk1 Staff ...»
The authors suggested that architectural factors were the cause of the lower infection rate in Building A. The ventilation system of Building A supplied 100% outside air to the building (eliminating mechanical recirculation) while the ventilation systems of the other buildings provided 30% or 70% recirculated air.
The Building A ventilation system also had additional air filters. Finally, the public areas of Building A were larger (per resident), reducing crowding that may facilitate disease transmission.
Milton et al. (2000) studied the association of the rate of outside air supply with the rate of absence from work caused by illness in 3720 workers located in 40 buildings with a total of 110 independently-ventilated floors. While absence is not synonymous with respiratory disease, a substantial proportion of short-term absence from work caused by illness results from acute respiratory illness.
Ventilation rates were estimated based on ventilation system design, occupancy, and selected end-of-day carbon-dioxide measurements, and buildings were classified as moderate ventilation (~ 12 L s-1 per occupant) or high ventilation (~24 L s-1 per occupant). The absence rate, controlling for age, gender, seniority, crowding, and type of workspace was 35% lower in the high-ventilation buildings.
The association of mold problems in buildings with the incidence of respiratory infections has been investigated in a few studies. One study (Husman et al. 1993, Husman 1996) compared the rates of acute respiratory infection in 158 residents of apartments with verified mold problems to the rates of infection in 139 residents of apartments without mold problems. Approximately twice as many residents of the moldy apartments reported at least one acute respiratory infection during the previous year.13 A complex multi-stage study examined the association of high mold exposures within day-care centers with common colds as well as other health outcomes in children (Koskinen et al. 1995, 1997) with inconclusive results (i.e., one comparison suggests that mold significantly increased serious persistent respiratory infections while other comparisons found small statistically insignificant decreases in common colds with higher mold exposure.) The recent evidence that mold exposures may adversely affect immune system function (Dales et al. 1998) is consistent with the findings of a positive association between molds and respiratory infections.
Population Affected and Cost of Communicable Respiratory Illness. Virtually everyone is affected by communicable respiratory illnesses. Averaging data from ________________
13Relative risk is 2.2, 95% CI is 1.2 to 4.4, adjusted for age, sex, smoking and atopy 1992 through 1994, the civilian non-institutional population experienced 43.3 common colds and 25.7 cases of influenza per 100 population (US Department of Commerce 1997), for a total of 0.69 illnesses per person per year.
The obvious costs of respiratory illness include health care expenses and the costs of absence from work. Additionally, respiratory illnesses may cause a performance decrement at work. In controlled experiments, Smith (1990) has shown that viral respiratory illnesses, even sub-clinical infections, can adversely affect performance on several computerized and paper-based tests that simulate work activities. The decrement in performance can start before the onset of symptoms and persist after symptoms are no longer evident.
Estimates of the productivity losses associated with respiratory illness are based on periods of absence from work and restricted activity days as defined in the National Health Interview Survey (U.S. Department of Health and Human Services 1994). In the U.S., four common respiratory illnesses (common cold, influenza, pneumonia, and bronchitis) cause about 176 million days lost from work and an additional 121 million work days of substantially restricted activity (Dixon 1985, adjusted for population gain). Assuming a 100% and 25% decrease in productivity on lost-work and restricted-activity days, respectively, and a $39,200 average annual compensation (U.S. Department of Commerce 1997), the annual value of lost work is approximately $34 billion.14 The annual health care costs for upper and lower respiratory tract infections total about $36 billion (Dixon 1985, adjusted for population gain and health care inflation). Thus, the total annual cost of respiratory infections is approximately $70 billion. Neglected costs include the economic value of reduced housework and of absence from school.
Potential Savings. Without being able to substantially change the buildingrelated factors that influence disease transmission, we cannot realize these health care cost savings and productivity gains. A number of existing, relatively practical building technologies, such as increased ventilation, reduced air recirculation, improved filtration, ultraviolet disinfection of air, and reduced space sharing (e.g., shared office), and reduced occupant density have the theoretical potential of reducing inhalation exposures to infectious aerosols by more than a factor of two.
The studies cited above suggest that changes in building characteristics and ventilation could reduce indexes of respiratory illness by 15% (absence from school) to 76% (influenza in nursing homes), with the strongest study (Brundage ________________
14A similar estimate, $39 billion, is obtained based on the information in Garabaldi (1985) et al. 1988) suggesting that a 33% reduction is possible. The amount of time spent in a building should influence the probability of disease transmission within the building. If efforts to reduce disease transmission were implemented primarily in commercial and institutional buildings15 that people occupy approximately 25% of the time, smaller reductions in respiratory illness would be expected in the general population than indicated by the building-specific studies. To adjust the reported decreases in respiratory illness for time spent in buildings, we estimated the percentage of time that occupants spend in each type of building (100% of time in jails and nursing home, 66% in barracks and housing, and 25% in offices and schools) and assumed that the magnitude of the influence of a building factor on the incidence of respiratory illness varies linearly with time spent in the building. After this adjustment and neglecting the Gulf War study involving some housing in tents and warehouses, the nine remaining studies cited above yield 11 estimates of potential decreases in metrics for respiratory illness (some studies had multiple outcomes such as influenza and total respiratory infections), ranging from 9% to 41% with an average of 19% (see Figure 2). Considering only the studies with explicit respiratory illness outcomes Adjusted % Decrease
15There are no technical barriers to implementation of similar measures in residences; however, business owners will have a stronger financial incentive to take action than home owners.
(i.e., excluding the study with an absence outcome) results in nine estimates of decreases in respiratory illness, adjusted for time in building, ranging from 9% to 41% with an average of 18%. The range is 9% to 20%, if the outlier value of 41% (illness in schools) is excluded. This narrower range is adopted, i.e., 9% to 20%, for the potential reduction in respiratory illness. With this estimate and 0.69 cases of common colds and influenza per person per year), approximately, 16 to 37 million cases of common cold or influenza would be avoided each year in the US.
The corresponding range in the annual economic benefit is $6 billion to $14 billion.
Allergies and Asthma
Linkage. Symptoms of allergies and of asthma may be triggered by a number of allergens in indoor air including those from house dust mites, pets, fungi, insects, and pollens (Committee on Health Effects of Indoor Allergens 1993). Allergens are considered a primary cause of the inflammation that underlies asthma (Platts-Mills 1994). There is evidence (e.g., Arshad et al. 1992, Wahn et al. 1997) that lower exposures to allergens during infancy or childhood can reduce the sensitization to allergens. Asthma symptoms may also be evoked by irritating chemicals, including environmental tobacco smoke (Evans et al. 1987). Viral infections, which may be influenced by building factors, also appear to be strongly linked to exacerbations of asthma, at least in school children. A recent study of 108 children, age 9 to 11, found a strong association of viral infections with asthma exacerbation (Johnston et al. 1995). Viral infections were detected in 80% to 85% of asthmatic children during periods of asthma exacerbation. During periods without exacerbation of asthma symptoms, only 12% of the children had detectable viral infections.16 Building factors most consistently and strongly associated with asthma and allergic respiratory symptoms include moisture problems, indoor tobacco smoking, house dust mites, molds, cats and dogs, and cockroach infestation (Committee on the Assessment of Asthma and Indoor Air 1999, Committee on Health Effects of Indoor Allergens 1993). Platts-Mills and Chapman (1987) provide a detailed review of the substantial role of dust mites in allergic disease.
In a recent review of the association of asthma with indoor air quality by the National Academy of Sciences (Committee on the Assessment of Asthma and Indoor Air 1999), the prevalence of asthma or related respiratory symptoms is increased by approximately a factor of two17 among occupants of homes or ________________
16The difference between infection rates is statistically significant, p 0.001 17Neglecting one study in the review with a very high odds ratio of 16.
schools with evidence of dampness problems or molds (Figure 3). In the same review, environmental tobacco smoke exposure, indicated by parental smoking, is typically associated with increases in asthma symptoms or incidence by 20% to 40%.
Data from few office-based studies are available for asthma and allergy associations with indoor environmental conditions. In case studies, moisture and related microbiological problems have been linked to respiratory symptoms in office workers (Division of Respiratory Disease Studies 1984, Hoffmann et al.
1993). In a study of office workers 18 (Menzies et al. 1988), higher relative humidity, higher concentrations of alternaria (a mold) allergen in air, and higher dust mite antigen in floor dust were associated with a higher prevalence of respiratory symptoms.
Overall, the evidence of a linkage between the quality of the indoor environment and the incidence of allergic and asthma symptoms is strong. Additionally, the exposures that cause allergic sensitization often occur early in life and are likely to occur indoors; consequently, the quality of indoor environments may also influence the proportion of the population that is allergic or asthmatic.
Population Affected and Cost of Allergies and Asthma. Approximately 20% of the U.S. population have allergies to environmental antigens (Committee on Health Effects of Indoor Allergens 1993) and approximately 6% have asthma ________________
18This was a case-control study of ~ 17% of all workers in the buildings.
(Rappaport and Boodram 1998). Drawing upon five recent papers, Fisk (2000b) has estimated that the annual costs for 1996 of allergies and asthma in the U.S. is $15 billion. Approximately $10 billion are health care costs and the remaining costs are indirect costs, for example the costs of lost work and school. A significant portion of the costs of allergies and asthma reflect the burden of these diseases in children.
Potential Savings from Changes in Building Factors. There are three general approaches for reducing allergy and asthma symptoms via changes in buildings and indoor environments. First, one can control the indoor sources of the agents that cause symptoms (or that cause initial allergic sensitization). For example, indoor tobacco smoking can be restricted to isolated separately-ventilated rooms, or prohibited entirely. Pets can be maintained outside of the homes of individuals that react to pet allergens. Perhaps even more broadly effective are measures that reduce the growth of microorganisms indoors. Changes in building design, construction, operation, and maintenance could reduce water leaks and moisture problems and decrease indoor humidities (where humidities are normally high), leading to a reduction in dust mites and molds in buildings.
Known reservoirs for allergens, such as carpets for dust mite allergen, can be eliminated or modified. Improved cleaning of building interiors and HVAC systems can also limit the growth or accumulation of allergens indoors. There are no major technical obstacles to these measures.
The second general approach for reducing allergy and asthma symptoms is to use air cleaning systems or increased ventilation to decrease the indoor airborne concentrations of the relevant pollutants. Many of the relevant exposures are airborne particles. Technologies are readily available for reducing indoor concentrations of airborne particles generated indoors. Better filtration of the outside air entering mechanically-ventilated buildings can also diminish the entry of outdoor allergens into buildings. Filtration is likely to be most effective for the smaller particles linked to allergies and asthma, such particles from tobacco smoke. Allergens that are large particles, e.g., from dust mites, have high gravitational settling velocities and are less effectively controlled by air filtration.
The influence of particle air cleaners on symptoms of allergies and asthma is reviewed by Committee on the Assessment of Asthma and Indoor Air (1999), and one more recent study is provided by van der Heide (1999). Many published studies have important limitations such as small air cleaners, a small number of subjects, or a focus on dust mite allergies which may be poorly controlled with air cleaners due to the large size and high settling velocities of dust mite allergens. Five of twelve studies involving subjects with perennial allergic disease or asthma reported statistically significant improvements in symptoms or airway hyperresponsiveness, or reduced use of medication when air cleaners were used. In six of seven studies, seasonal allergic or asthma symptoms were significantly reduced with air cleaner use. Subjects were blinded, i.e., unaware of air cleaner operation, in only two of these studies involving seasonal symptoms;