Fact checked byKristen Dowd

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June 07, 2023
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Upper respiratory infection risk in asthma elevated with high classroom relative humidity

Fact checked byKristen Dowd
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Key takeaways:

  • The risk for upper respiratory infections in children with asthma went up when they were taught in classrooms with high relative humidity.
  • Classroom temperature was not linked to upper respiratory infections.

WASHINGTON — In elementary school children with asthma, greater relative humidity in classrooms heightened the risk for upper respiratory infections, according to research presented at the American Thoracic Society International Conference.

Peggy S. Lai

“It is not surprising that there are building-specific factors that impact respiratory viral infections; however, this really highlights a gap in the field,” Peggy S. Lai, MD, MPH, of Massachusetts General Hospital, told Healio. “Most school studies are based on models or laboratory conditions that simulate schools. Lab studies are ‘perfect’ conditions; field studies performed in schools reflect real life. If we can find what built environment factors impact the risk of viral infections in students and teachers, then we have the potential to develop public health interventions focused on environmental interventions that are durable because they don't rely on individual behaviors (like masking, vaccine mandates) that are hard to enforce over the long term.”

School classroom
In elementary school children with asthma, greater relative humidity in classrooms heightened the risk for upper respiratory infections, according to research presented at the American Thoracic Society International Conference. Image: Adobe Stock

Lai and colleagues at Massachusetts General Hospital and Boston Children’s Hospital evaluated 236 elementary school children (mean age, 8.1 years; 48% girls) with mild persistent asthma in the Northeastern U.S. over 1 year to evaluate how classroom environment factors, such as carbon dioxide, relative humidity and temperature, impact the risk for upper respiratory infections (URIs).

Throughout the school year, researchers utilized the Smart Home Weather Station (Netatmo) to track these factors in the classroom for 2-week periods, according to the abstract.

To see how many children developed a URI, the child’s parents/caretakers were given a standardized symptoms survey to complete every 2 months.

Further, to find out how classroom temperature and relative humidity were related to URIs, researchers employed statistical models that accounted for season (based on day of the year) and indoor air quality (based on carbon dioxide levels of the classroom). Age, race and gender were also counted in as covariates.

Of the total cohort, 93% of children had a self-reported URI during the school year with a per child average of 4.2 (standard deviation, 3) URIs during that time.

When evaluating carbon dioxide levels in classrooms, the median was 810 ppm, and poor indoor air quality (> 1,000 ppm) was observed 18.7% of the time, according to the abstract. Additionally, the researchers reported an average 43.4% (interquartile range, 34.8%-50.9%) relative humidity in this study.

Researchers found a linear relationship between relative humidity and URIs, with a greater risk for a URI with every increase in relative humidity of 1% (adjusted incidence rate ratio, 1.015; 95% CI, 1.001-1.03). In contrast, classroom temperature was not linked to URIs.

A nonlinear relationship was found between season and URIs, as well as carbon dioxide levels and URIs, according to the abstract. Future work focuses on testing for respiratory viruses collected from students during the school year, Lai told Healio.

“The findings indicate the potential that there are interventions focused on buildings to make them safer,” Lai told Healio. “[In terms of future studies,] we need more field studies in schools.”