Indoor air quality in schools and daycare environments can affect millions of people including students and staff. In the US, more than 50 million children are enrolled in public and private schools, and more than half of the children ages 3–5 have attended center-based childcare programs over the past decade.53
Asthma and allergies are important public health concerns, not only in terms of health care costs but also in terms of lost productivity and reduced quality of life. For example, asthma and allergies account for more than 16 million missed school days per year in the US.54, 55
Among school-aged children, asthma is the leading cause for absenteeism and can influence a child's academic performance and ability to participate in school related activities.56
Importantly, the burden of asthma in schools extends beyond children; a recent report suggests that asthma within the educational services industry is an occupational health problem, particularly among teachers and teacher's aids.57
Although people tend to spend the majority of their time at home,58
allergen exposures can be encountered in environments other than the home. Schools and daycare centers, where children and teachers spend a large part of their time, may be important sites for indoor allergen exposures. Especially for younger children, the timing of exposure can be critical because IgE-mediated sensitivity to specific aeroallergens develops in early childhood.59
In daycare and elementary school classrooms, which often have a variety of potential allergen reservoirs (e.g., upholstered furniture, pillows, stuffed animals and toys), exposure levels may be higher than in middle and high school classrooms.16, 26
Moreover, the disturbance of allergen reservoirs is more likely because children at younger ages are more physically active.
Remarkably few studies to date have evaluated the relationship between asthma and allergy related outcomes and indoor allergen exposures in school and daycare environments. Most studies that assessed allergen exposures in these environments were primarily designed to determine exposure characteristics. Although some studies reported prevalence rates for atopic outcomes, few studies used multivariate analysis to investigate relationships between health outcomes and exposures. Only a small number of the reviewed studies assessed allergen levels simultaneously in school and home environments (Tables E1-E5).
In schools and daycares where occupant density is high, the magnitude of indirect exposure to pet allergens may be sufficient to induce or maintain symptoms. Indeed, several Swedish studies have suggested that indirect exposure to cat and dog allergens in schools may influence asthma morbidity.25, 60, 61
In a recent study, asthmatic children who had diagnosed cat allergy, but did not report any direct contact with pets, were evaluated after they returned to school following summer break. Those children who attended classes where more than 18% of the students owned cat(s) reported significantly decreased peak expiratory flow rates, more asthma symptom days, and increased use of asthma medication than children who attended classes with fewer cat owners (≤ 18%).60
Another study demonstrated that asthmatic children with cat and dog sensitivity had significantly increased bronchial reactivity to inhaled methacholine after one school week.61
In this study, concentrations of cat and dog allergens were found higher in school dust than in dust collected from children's homes, suggesting greater exposure in school than in home. Among Swedish schoolchildren, cat allergen levels in dust samples have also been associated with the incidence of asthma diagnosis.32
Recently, a German study examined whether exposure to cat allergen in the school environment was associated with allergic sensitization rates.62
Among school-aged children who did not have regular contact with cats, cat-specific sensitization rates increased with in a dose-response fashion, depending on the percentages of students in class or school reporting regular contact with cats.
In the US, only one study has examined asthma prevalence in relation to the presence of common indoor allergens in the school environment. This study found a positive correlation between asthma prevalence rates and levels of cockroach allergen in schools.18
Over the past decades, numerous studies have reported positive associations between respiratory morbidity (e.g., asthma) and exposure to fungi in indoor environments,63, 64
including schools and daycare centers.65-68
However, the underlying mechanisms for the observed health effects are not well characterized. Although fungal allergens can induce IgE-mediated hypersensitivity, 69
exposure to fungi may also induce non-IgE-mediated inflammatory and immunological processes; particulates derived from fungi not only contain allergens but also contain a variety of biologically active molecules (e.g., β-1,3-glucans).3, 70
It has also been suggested that fungal exposure may promote adjuvant effects on allergic immune responses.71
In summary, although published studies demonstrate the importance of the school environment, the relationship between allergic respiratory diseases and indoor allergen exposures in schools and daycares is not well characterized. Although studies suggest that exposure to pet allergens in schools may influence asthma morbidity, studies provide limited information on whether exposures to indoor allergens in schools and daycares contribute to the development of allergic sensitization and asthma.