By Kathryn Doyle

(Reuters Health) – - Mouse allergens in school buildings may be an important environmental factor aggravating kids’ asthma, a U.S. study suggests.

Researchers found mouse allergen in nearly 100 percent of dust samples from the schools studied, and exposure to it was linked to increased symptoms and decreased lung function among children with asthma.

“We always hypothesized that the school was important, but this study comprehensively evaluated school and home environments,” said senior author Dr. Wanda Phipatanakul of Boston’s Children’s Hospital and Harvard Medical School.

Most research on this question has focused on homes, not schools, she told Reuters Health by email.

The researchers evaluated 284 students with asthma aged 4 to 13 years who were enrolled in 37 inner city elementary schools between 2008 and 2013. The kids had clinical exams before the start of the school year and were observed for the following year, including keeping count of their days with asthma symptoms, asthma-associated healthcare use and lung function.

Over the same year, classroom and home dust samples were collected and analyzed for common allergens, like rat, mouse, cat and dog allergens and dust mites.

Mouse allergen was present in 441 out of 443 school dust samples, or 99.5 percent, cat allergen in 420 samples, or about 95 percent, and dog allergen in 366 samples, or about 83 percent.

Kids exposed to the highest mouse allergen levels, compared to those exposed to the lowest, were 27 percent more likely to experience asthma symptoms on any given day and scored about 4 points lower on tests that measured how well their lungs worked when they exhaled.

“There is no known ‘danger’ level of allergens and allergens are ubiquitous in our environment - homes, schools, and all public places in a variety of environments,” Phipatanakul said.

“The study just provides evidence that schools are important and resources and support to help the schools could be beneficial,” she said.

The study took into account kids’ exposure to allergens at home, and did not find any associations between school exposure to the other indoor allergens tested and worsening asthma outcomes, according to the report in JAMA Pediatrics.

“In home environments many allergens have been found to be important, but in many inner-city home studies, mouse allergen and cockroach allergen were found to be important,” Phipatanakul said.

Air filtration and pest management may help reduce allergen levels, she said.

“Schools are already doing the best they can with the resources they have,” she added.

Allergens have been found, sometimes at high levels, in schools, daycares and other public use buildings, said Dr. Elizabeth C. Matsui of Johns Hopkins School of Medicine in Baltimore who coauthored an accompanying editorial.

“In this particular study, it was puzzling that the association between mouse allergen levels and asthma symptoms did not depend on whether the child was allergic to mice,” Matsui told Reuters Health by email. “This suggests that perhaps the mouse allergen is not causing the asthma symptoms, but instead may be a marker of some other exposure(s) that are triggering the asthma symptoms.”

Even so, Matsui and her coauthor write in the editorial, “One of the study’s significant contributions is that it highlights the importance of collaborating with schools to understand the effect of the school environment on student health."

SOURCE: http://bit.ly/2gcHHUW and http://bit.ly/2fOfSoY JAMA Pediatrics, online November 21, 2016.