Ulla Haverinen-Shaughnessy

Background: The physical school environment is a key factor influencing illness-related absences, particularly those caused by infectious diseases transmitted through air and surfaces. Previous studies, often underpowered, have been unable to conclusively quantify the impacts of improved classroom indoor environmental quality (IEQ) on illness-related absences, while also accounting for sociodemographic factors, such as gender and ethnicity. Objective: This study evaluates the impacts of district-wide renovations on student absences due to specific illness types, based on exceptional district data on daily absenteeism and socioeconomic factors, covering 1217 school days and 45,428 students. Methods: Between 2016 and 2021, over 45 schools in a district located in a mountain west region of United States underwent comprehensive renovations, which included upgrading heating, ventilation, and air conditioning systems. At the same time, cleaning protocols were developed to reduce surface contamination. Data from pre- and post-renovation monitoring included classroom temperature, relative humidity, and surface biocontamination levels. Carbon dioxide levels were used to estimate ventilation rates, while temperature and relative humidity were used to estimate absolute humidity. Results: Independent associations between illness-specific absences and school renovations, along with several IEQ parameters, were quantified. Based on the results, over one-third of absences due to respiratory illnesses could be reduced by keeping school facilities up to date and adhering to recommended standards for ventilation. Increased frequency of cleaning could help to reduce absences due to gastrointestinal illnesses. Additional reductions could be achieved by maintaining higher humidity and cooler temperatures in classrooms. Significance: These findings highlight the importance of maintaining good IEQ in schools, resulting in fewer absences from infectious diseases. Impact: The study is based on a large-scale natural experiment, incorporating daily student-level absence data specifying illness types and background information for all students in the district, collected over seven school years - the longest follow-up period to date, to our knowledge. These data, combined with state-of-the-art IEQ monitoring conducted before and after the renovation of 45 schools, provides superior statistical power to quantify the impacts of renovations and how IEQ parameters may partially explain their effects on illness-related absences. The findings can inform policies at the school, district, and national levels, guiding renovations, maintenance and operational practices aimed at reducing airborne pathogens and surface contamination, and reducing illness-related absenteeism in schools.