Issue link: https://hi.iaq.net/i/191637
Climate Change, the Indoor Environment, and Health INFECTIOUS AGENTS AND PESTS 159 enced by the number of air exchanges in the work environment. Singleton and colleagues (2010) found that HRV was recovered from 44% of Alaskan native children hospitalized with a respiratory infection, but this rate was quite close to that in control children who were not hospitalized. Tovey and Rawlinson (2011) note that the rates of asthma rise precipitously two to three weeks after the start of school, indicating that some new exposure in the classroom is responsible. The authors hypothesize that these factors include HRV as well as numerous other costimulators of asthma such as endotoxin, proteins, and allergens. du Prel and colleagues (2009) found that HRV rates are associated with higher humidity levels, which might become more common as a result of climate change. Gram-Negative Bacteria The gram-negative bacteria present special issues in climate-associated infectious-disease epidemiology. They are not dependent on human-tohuman spread, are not dependent on human inhabitation for survival, and have the ability to form biofilms—slippery, poorly penetrable slimes that cover the inside of water conduits. Given their close ties to the environment and their access to humans through water consumption, aerosol generation, heating, and cooling, the epidemiology of gram-negative rod infections is a window into infectious diseases in the setting of climate change. Legionella From its initial recognition as a cause of human respiratory disease, Legionella infection has been closely tied to water-droplet exposure in hotels and hospitals (Stout and Yu, 1997). However, the modes of transmission clearly can involve both aerosol spread (by water misters in grocery stores, for example) and aspiration. Spread from potting soil has also been well documented (de Jong and Zucs, 2010). Regardless of the exposures or the modes of transmission, it is clear that legionellae are relatively common in some water supplies and has seasonal variation. In a case-crossover study in the greater Philadelphia area, Fisman and colleagues identified summertime occurrence of reported Legionella pneumonia to correlate with rainfall and increased relative humidity in the preceding week or so, rather than temperature (Fisman et al., 2005). Whether that reflects increased recruitment of legionellae into the water supply through rainfall, increased survival in higher humidity, indoor transmission, or outdoor transmission remains to be concretely determined. However, it is clear that in many instances, such as in hospitals, Legionella transmission is presaged by high levels of bacterial or bacterial DNA recovery from ambient water sources, such as faucets (Feazel et al., 2009). This Copyright © National Academy of Sciences. All rights reserved.