Household mold as a predictor of asthma risk: Recent progress, limitations, and future directions

Abstract

Asthma prevalence in the United States increased dramatically from 1980 through 1997 and has continued to increase, albeit at a slower pace, over the past decade. Some have speculated that this upward trend is, at least in part, related to modern housing construction, which tends to increase indoor exposures. Installation of central heating systems and highly insulated windows has been shown to decrease air-exchange rates, increase indoor temperature and absolute humidity, and increase levels ofmold in carpet dust. The presence of mold spores in the indoor environment is not in itself a problem when the source is the normal interchange of outside air and when the amount and types of spores inside are the same or less than outside. However, in the setting of inadequate or poorly maintained ventilation systems that might not provide enough air for dilution or dehumidification and the presence of water in materials or condensation from high humidity, mold can actively grow on indoor substrates, potentially adding unhealthy chemicals and bioaerosols to the indoor air. There is now a fairly robust body of evidence suggesting that living in moldy households increases the risk of childhood asthma. Early cross-sectional and case-control studies had reported an association between asthma development and household moldiness crudely measured by identifying moldy odors or signs of water damage in homes. Investigators from the Cincinnati Childhood Asthma and Air Pollution Study have strengthened the evidence for causation in a series of articles that have observed significant relationships between mold levels collected in household dust during infancy and subsequent development of recurrent wheeze and asthma at 1, 3, and 7 years of age. The prospective design of this birth cohort study minimized the potential for recall bias that can occur in cross-sectional and case control studies (eg, parents might be more likely to recall moldy odor if their child has asthma). Instead of relying on subjective identification of moldy households, dust samples were assayed by polymerase chain reaction (PCR) for common mold species. A quantitive and standardized designation of moldiness for each household was used called the Environmental RelativeMoldiness Index (ERMI). The ERMI is a method to quantify household moldiness based on the difference in levels of 26 mold species