Classroom dust bacteria linked to reduced lung function in children across Europe

Researchers studying nearly 300 classrooms across 22 European countries have found that two common types of bacteria living in classroom dust are linked to measurably reduced lung function in children. The discovery, presented at the European Respiratory Society Congress in Barcelona, suggests that the invisible microbial landscape of a school building may shape how well a child's lungs develop and perform.

Dr. Soutrik Banerjee and his team at the University of Ferrara, working with the French technology company Alten S.A., focused on two bacterial groups: Streptomyces and Mycobacterium species, both naturally present in soil, dust, and water systems. The researchers collected dust samples from classrooms and measured bacterial concentrations, then tested the lung function of children in those same rooms using spirometry—a standard breathing test in which a child inhales deeply and exhales as forcefully and quickly as possible into a measuring device. The test quantifies how much air the lungs can hold and how rapidly that air moves in and out.

The findings were striking in their specificity. Children in classrooms with higher Streptomyces levels showed a 0.08-litre reduction in forced vital capacity, the maximum volume of air a child can exhale after a full breath. Those exposed to elevated Mycobacterium had slightly lower readings in two other measures: a 0.06-litre reduction in FEV₁, which tracks how much air exits in the first second of exhalation, and a 0.13-litre-per-second reduction in peak expiratory flow, the fastest rate at which air can be expelled. The researchers accounted for age, gender, body mass index, secondhand smoke exposure, pet allergens, socioeconomic factors, building age, geographic region, and local air pollution levels—a rigorous adjustment that strengthens confidence in the association.

These reductions are modest when measured in a single child, but Banerjee emphasized their statistical significance and population-level importance. A child spends roughly 180 days a year in the classroom, five days a week, breathing the same air. A mild to moderate loss of lung capacity in childhood, he noted, may foreshadow preventable respiratory disease later in life. Reduced lung function limits oxygen intake and the body's ability to clear carbon dioxide, producing fatigue and shortness of breath.

The mechanism remains uncertain. Banerjee proposed two pathways: the bacteria might directly irritate airways or trigger immune and inflammatory responses in developing lungs. Alternatively, the bacterial presence could signal broader environmental problems—poor ventilation, dampness, inadequate cleaning, or outdoor dust infiltration—that are themselves damaging to respiratory health. The bacteria may be a symptom rather than the sole cause.

Professor Alexander Möller of the University Children's Hospital Zurich, who reviewed the study, cautioned against interpreting the findings as a call for sterile classrooms. Instead, he framed the research as evidence that school buildings matter for children's health. His practical recommendations centered on fundamentals: adequate ventilation, control of moisture and mold, regular cleaning, and proper maintenance. These measures cost money and require sustained attention, but Möller suggested the investment pays dividends in protecting developing lungs.

The study does not explain why these particular bacteria accumulate in some classrooms more than others, nor does it establish whether removing them would restore lung function. It does establish a measurable association across a large, geographically diverse sample—a foundation for further investigation and, potentially, for schools to reconsider how they manage their indoor environments.