Tehran University of Medical Sciences Journal of Air Pollution and Health 2476-3071 10 3 2025 09 15 395 410 Bibi Ally Charles Department of Medical Laboratory Sciences, School of Allied Health, College of Medical Sciences, University of Guyana, Georgetown, Guyana Ede Tyrell Department of Medical Laboratory Sciences, School of Allied Health, College of Medical Sciences, University of Guyana, Georgetown, Guyana Kevin Hohenkirk Savanna La Mar General Hospital, Westmoreland, Jamaica Andrew Hutson School of Medicine, College of Medical Sciences, University of Guyana, Georgetown, Guyana Obena Vanlewin Department of Medical Imaging, School of Allied Health, College of Medical Sciences, University of Guyana, Georgetown, Guyana 2024 09 16 2025 08 26 Introduction: Indoor environment contributes to human health and productivity. The absence of climatic control systems may lead to microbial contamination. The air quality of public institutions should be monitored. Therefore, this study was conducted to determine the microbial load of the air in the main library at the University of Guyana and to evaluate the effectiveness of a disinfection intervention on the microbial load of the air. Materials and methods: This was an experimental- observational study involving three phases: analyzing the microbial quality of the air, a disinfection experiment, and a disinfection intervention. Phase 1 was done before the rehabilitation of the library, Phase 2 was done during the rehabilitation, and Phase 3 was carried out after the rehabilitation and the disinfection intervention. Samples were collected on settle plates and incubated. ColonyForming Units (CFUs) were enumerated and the microbial load was determined using a standardised equation. Several disinfectants were tested against two bacteria and a specific disinfection protocol was developed for the disinfection intervention. Results: The bacterial load for Phase 1 (13,114 CFU/m3) and Phase 2 (7,636 CFU/m3) was higher than that of Phase 3 (4,648 CFU/m3). There was an extremely high fungal load (4,067 CFU/m3) before the disinfection intervention but no growth after. Conclusion: We concluded that a high microbial load was found in our study before the disinfection intervention which was considerably diminished after the intervention. We recommend implementing the cleaning regimen we developed as part of the library’s cleaning protocol. https://japh.tums.ac.ir/index.php/japh/article/view/821 https://japh.tums.ac.ir/index.php/japh/article/download/821/449