High mold levels in urban homes linked to difficult-to-control asthma among youth

Mucor levels in urban homes where youth resided predicted difficult-to-control asthma, and these levels appeared more likely in homes with window air conditioning units, according to a study.

Difficult-to-control (DTC) asthma — indicating a lack of symptom control despite high-dose inhaled corticosteroids and maximal add-on therapies — is more prevalent among urban, nonwhite and under-resourced populations, according to Stephen J. Vesper, MS, PhD, of the U.S. Environmental Protection Agency Center for Environmental Measurement and Modeling, and colleagues.

DTC asthma also may lead to more frequent exacerbations, a poorer response to medication and less lung function than easy-to-control (ETC) asthma.

The Asthma Phenotypes in the Inner City (APIC) study showed that participants with DTC asthma — defined as requiring daily therapy of 500 g or more of fluticasone, with or without a long-acting beta-agonist — had significantly more common sensitization to mold, but not to dust mites, roaches, rodents, pets, pollen, peanuts or other foods compared with participants with ETC asthma, defined as requiring 100 g or less of fluticasone.

The researchers conducted a post-hoc analysis of APIC dust samples from homes in Baltimore, Boston, Chicago, Cincinnati, Denver, Detroit, New York City and Washington, D.C., using the Environmental Relative Moldiness Index (ERMI) panel of 36 molds.

Group 1 in ERMI includes 26 molds that indicate water damage in the home, whereas Group 2 includes 10 species that primarily originate outdoors and are commonly found indoors, even in homes that do not have water damage. Higher ERMI values indicate greater mold contamination in the home.

The APIC study initially collected 485 dust samples from the homes of children aged 6 to 17 years with DTC and ETC asthma by horizontal wiping above floor surfaces with a cloth. The current study assessed 265 of these samples that were frozen and held at –20°C. The median age of children represented in those samples was 11 years, and 57.73% were male.

The results, published in The Journal of Allergy and Clinical Immunology, showed no significant difference between the average summed logs of the Group 1 and Group 2 molds found in the homes of children with DTC and ETC asthma, nor were the average ERMI values significantly different between these homes, indicating that total mold contamination was not a distinguishing factor in asthma-control difficulty.

After comparing the average concentrations of each of the 36 molds in ERMI, however, the researchers found that Mucor — a microbial genus of approximately 40 mold species in the Mucoraceae family — was the only mold with a significantly greater concentration in homes of those with DTC asthma than those with ETC asthma (295 vs. 67 cell equivalents/mg dust; P < .001).

The researchers noted that Mucor grows in and around air conditioning (AC) systems and ducting due to condensation, especially if the unit is not cleaned or the filter is not changed regularly, so the researchers examined the occurrence of window AC units in these homes as well.

Mucor concentrations were a significant predictor of the probability of DTC asthma (P = .007) in homes with window AC units, but not in homes that did not have window AC units. In fact, Mucor concentration contributed an approximately 22% increase (OR = 1.6; 95% CI, 1.2-2.2) in the ability to discriminate between cases of DTC and ETC asthma.

The researchers called their results consistent with previous studies that identified mold exposures as relevant to the difficulty of controlling asthma. But they cautioned that they did not quantify other potential exposures, such as other molds and contaminants inside and outside the home, so high concentrations of Mucor only may be an indicator, not a cause, of DTC.

Further, the researchers wrote, new approaches are needed to help children with DTC asthma, including elimination of the conditions that contribute to high levels of Mucor.