Dual burden of PM and airborne viruses in primary schools: A pilot study in Patras, Greece

Background

Children spend substantial time in schools, yet indoor air quality (IAQ) and airborne pathogen burden remain under-characterised. Following 2021 WHO Air Quality Guidelines (AQG), this study quantified the gap between recommended standards and real-world conditions while assessing exposure to airborne respiratory viruses as a combined public health risk.

Methods

In March 2026, air sampling was conducted in 28 classrooms across seven primary schools in Patras, Greece. Triplicate PM2.5/PM10 measurements were obtained alongside RT-qPCR detection of airborne SARS-CoV-2, hMPV, RSV, rhinovirus, and influenza A. Non-parametric tests (Mann-Whitney U, Kruskal-Wallis) and Cliff’s delta evaluated ventilation and occupancy effects. Reliability: RSD<5%.

Results

Mean PM2.5=37.8 µg/m³; mean PM10=109 µg/m³. All classrooms exceeded WHO 24-hour AQG limits. At least one respiratory virus was detected in every classroom; SARS-CoV-2 most frequent. No significant urban/peri-urban differences (p > 0.5), indicating indoor sources and regional background outweigh local traffic. Frequent natural ventilation was associated with lower particulate concentrations (p < 0.033, Cliff’s delta>0.58) and reduced viral RNA detection. PM2.5/PM10 ratio=0.35 suggests dust resuspension as the dominant indoor PM source.

Conclusions

Primary school children in Patras face dual exposure to elevated particulate pollution and airborne viruses. Natural ventilation is a highly effective, low-cost, equitable intervention. Aligning school infrastructure and policies with WHO AQG, alongside standardised ventilation protocols, offers a sustainable strategy to reduce chronic environmental and acute infectious risks.

Key messages

• Greek schoolchildren face simultaneous chronic particulate matter and acute (virus) airborne hazards, undocumented until now.

• Mandating WHO-aligned ventilation protocols in schools can mitigate both environmental and infectious disease burdens simultaneously.