NEW YORK (Reuters Health) - Although an estimated 7.5% of children nationwide have asthma, the prevalence of asthma among students at many Baltimore schools ranges from 10% to 20%. New study findings suggest that this higher prevalence may be due to students' exposure to dust mites and other allergens trapped in their school's carpets and rugs.

"Unless there is a thorough, frequent cleaning--vacuuming--with an HEPA filter to stop the dust from being re-suspended, avoiding wall-to-wall carpet and/or rugs is highly recommended for the schools," study author Dr. Sania Amr, an occupational and environmental medicine physician at the University of Maryland School of Medicine, told Reuters Health.

For their study, Amr and her colleagues, along with the study's lead author Dr. Mary E. Bollinger, collected and analyzed dust samples from 10 different sites in 12 Baltimore schools with asthma prevalences ranging from 2% to 27%.

"Overall, the levels of indoor allergens in Baltimore City public schools were low," the investigators report. "However, the presence of carpet or rugs led to significantly higher allergen levels potentially capable of causing asthma symptoms and sensitization."

The presence of rugs or carpets was associated with higher levels of dog allergens and dust mites, both of which correlated with higher asthma prevalence in schools, study findings show. Rugs and carpets were also linked to higher levels of mouse and cat allergens, while asthma prevalence in schools was also associated with higher levels of cockroach allergen, the researchers report.

"Carpet and rugs trap dust and whatever the dust contains," Amr said. "People sit on the rugs (and) carpet--especially children; they also wipe their shoes and whatever they bring on the soles from home or outside."

Dust samples from teachers' lounges and school cafeterias reportedly contained the highest average levels of both cockroach and mouse allergen. Samples from the kindergarten and 2nd grade classrooms revealed equally high levels of cockroach allergen.

"One way to reduce the presence of these allergens is to eliminate some of the reservoirs, and that is carpet (and/or) rug," Amr said. "In addition, the absence of carpet and rug makes it easier to clean floors and especially mop them--mopping with a wet rag reduces airborne dust, and its redistribution in a room."

Further, this recommendation applies "not only to the schools, but (also) to the homes of children with asthma," Amr said.

The findings were presented this month in New York during the American Academy of Allergy, Asthma and Immunology's 58th annual meeting.