Children in classrooms with higher levels of two common soil bacteria had measurably lower lung function than children in classrooms with less of them, according to an analysis of nearly 300 classrooms across 22 European countries presented in Barcelona.
The differences were small in absolute terms and consistent in direction. Higher levels of Streptomyces in classroom dust were associated with 0.08 liters lower forced vital capacity, a measure of how much air a child can blow out after taking a deep breath. Higher levels of Mycobacterium species were associated with 0.06 liters lower forced expiratory volume in one second and 0.13 liters per second lower peak flow, both measures of how fast air moves out of the lungs. The researchers adjusted for age, gender, body mass index, passive smoking, pet allergens, socioeconomic indicators, school building age and region, and local air pollution levels.
The word doing the most work in that sentence is associated. This study measured bacterial levels in dust and lung function in children at the same time. It did not show that the bacteria caused the reduction, and the researchers did not claim it did.
The Dataset and the Two Organisms Involved
The work drew on SINPHONIE, a European school environment study covering 22 countries and close to 300 classrooms. Researchers measured concentrations of Streptomyces and Mycobacterium species in settled classroom dust and tested children from each classroom with spirometry, the standard breathing test in which a child takes a deep breath and blows out as hard and fast as possible.
Both bacterial groups are ordinary rather than exotic. They live in soil, dust, and water systems, and they turn up in indoor environments routinely. That is part of why the finding is interesting and part of why it is hard to interpret. These are not contaminants that point to a specific failure. Their presence may instead be a marker of something else about a room, such as dampness, poor ventilation, cleaning practices, or how much outdoor dust gets tracked in.
The study was presented by Dr Soutrik Banerjee of the Department of Environmental and Prevention Sciences at the University of Ferrara in Italy, working with the French technology company Alten S.A. Banerjee said the team wanted to test whether higher classroom exposure to these bacteria is linked to children's lung health across Europe, noting that indoor air quality research in schools has focused far more on pollutants, humidity and ventilation than on which specific bacteria are growing in the dust. "The bacteria may either have a direct biological effect," he said, or they may be indicators of other indoor conditions that influence lung function. The commercial affiliation is disclosed in the materials released with the presentation.
Reading the Size of the Effect Honestly
A difference of 0.08 liters in forced vital capacity is not something a parent would notice in a child, and it is not a diagnosis. For an individual healthy child, a difference of that size falls within the range of normal variation between one test and the next.
Where it matters is at population scale and across time. Lung function in childhood follows a growth trajectory, and researchers increasingly think that where a child lands on that curve by early adulthood shapes respiratory risk decades later. Banerjee made the same argument, describing the reductions as modest for each child but potentially important for the wider population because children are in classrooms every weekday. Small average shifts across a whole school population are a different kind of signal than a small shift in one child. They point at the room rather than the individual.
The study also cannot separate the bacteria themselves from whatever conditions allow them to accumulate. A classroom with high Streptomyces levels may also be a classroom with a damp corner, an aging ventilation system, or a window that never opens. Each of those has its own established relationship with children's breathing, and this analysis was not designed to tell them apart.
The Limits That Matter Before Anyone Acts
The findings were presented as a conference abstract and have not been published in a peer-reviewed journal, so the full methods have not been through external review. Cross-sectional measurement means bacteria and lung function were captured at one point in time, which cannot establish sequence, let alone cause.
There is also a geographic limit that American readers should hold onto. The classrooms were European, and there is no equivalent public dataset pairing bacterial dust measurements with spirometry in United States schools. That absence does not mean the pattern would differ here. It means nobody has checked, and the finding cannot be transplanted onto a specific American district without that work.
The society's own framing was cautious. Professor Alexander Möller, head of the European Respiratory Society's Paediatric Assembly and professor of pediatric pulmonology at the University Children's Hospital Zurich, who was not involved in the research, said the results support the idea that healthy school buildings matter. "The practical message is not that schools should become sterile environments," he said, pointing instead to ventilation, dampness control, regular cleaning and building maintenance.
Reasonable Steps for Parents and School Districts
Nothing in this study warrants alarm about sending a child to school, and no health authority has changed guidance based on it. Parents do not need to have classroom dust tested, and there is no consumer test a household could act on.
What the finding does support is attention to the parts of school buildings already understood to affect children's breathing. Functioning ventilation, prompt repair of leaks and water damage, and routine cleaning of settled dust are established practices with independent justification, and they line up with existing guidance on school air quality. Districts that upgraded HVAC systems with federal pandemic relief funding have already done a version of this work, and districts that did not are the ones where the underlying conditions are most likely to persist.
Parents of children with asthma have a more specific interest. If a child's symptoms reliably worsen on school days and improve during breaks, that pattern is worth raising with both a clinician and the school, independent of this study. It may reflect the building, or allergens, or something else entirely, and it is addressed through an asthma action plan and, where warranted, a conversation with school administrators about the classroom itself.
Researchers presenting at the ERS Congress in Barcelona framed the work as a step toward understanding what makes schools healthy environments for developing lungs rather than as grounds for intervention. That framing is the right one. The next step is longitudinal work following the same children over time, and studies designed to separate the bacteria from the building conditions that let them accumulate.
Until that exists, the useful takeaway for families is narrow. School buildings shape children's breathing; the evidence for that is broader than this one study, and the levers that matter are held by districts rather than households.
Key Questions Answered
What did researchers measure? Levels of Streptomyces and Mycobacterium species in settled classroom dust, paired with spirometry results from children in those classrooms, across nearly 300 rooms in 22 European countries.
How big were the differences? Higher Streptomyces levels were associated with 0.08 liters lower forced vital capacity. Higher Mycobacterium levels were associated with 0.06 liters lower forced expiratory volume in one second and 0.13 liters per second lower peak flow.
Does this mean the bacteria damaged children's lungs? No. The study found an association at a single point in time. It cannot show that the bacteria caused the difference, and other classroom conditions could explain both.
Are these unusual bacteria? No. Both groups are common in soil, dust, and water systems and are found indoors routinely.
Should parents have their child's classroom tested? No. There is no consumer test that would produce actionable information, and no health authority has recommended testing.
Does this apply to American schools? Unknown. No comparable public dataset pairs bacterial dust measurements with children's lung function in United States classrooms.
What should a parent do if a child's asthma worsens at school? Raise the pattern with a clinician and with the school. That is worth doing regardless of this study, and it is addressed through an asthma action plan and building-level questions.
