Assessment of Indoor Airborne Microorganisms in a Densely Populated Malaysian Public University

Background and Context

Indoor air quality (IAQ) is a significant public health concern, particularly in tropical countries like Malaysia where the warm, humid climate favours microbial growth and where buildings extensively utilise air-conditioning systems that continuously recirculate indoor air. Modern humans spend approximately 90% of their time indoors, and the composition of indoor air — including its biological component of bacteria, fungi, and other microorganisms — directly impacts respiratory health, allergic sensitisation, and overall well-being of occupants.

University buildings represent a category of indoor environment with particularly high relevance to IAQ concerns. Lecture halls, tutorial rooms, libraries, and common areas accommodate large numbers of occupants in relatively enclosed spaces, often for extended periods. The high occupant density generates elevated levels of bioaerosols through breathing, coughing, sneezing, and skin shedding, while the air-conditioning systems designed to maintain thermal comfort may inadvertently create conditions that support microbial proliferation if not properly maintained.

In Malaysia, the Department of Occupational Safety and Health (DOSH) published the Industry Code of Practice on Indoor Air Quality (ICOP IAQ) in 2010, establishing acceptable limits for various indoor air pollutants including biological contaminants. The code specifies maximum acceptable concentrations for total bacterial counts and total fungal counts in indoor air, providing a regulatory benchmark against which IAQ monitoring results can be evaluated. However, compliance monitoring in educational institutions has been limited, and the microbial ecology of Malaysian university buildings remains incompletely characterised.

Study Design and Methodology

This study assessed the concentrations and composition of airborne microorganisms (bacteria and fungi) in the indoor environment of a densely populated Malaysian public university. Air sampling was conducted across multiple building types and functional spaces — including lecture halls, laboratories, office areas, and corridors — to capture the variability in microbial loads across different usage contexts. Culturable airborne microorganisms were collected using single-stage impaction samplers (biosamplers) in accordance with the National Institute of Occupational Safety and Health (NIOSH) Manual Analytical Method 0800, which is the reference method specified by the Malaysian ICOP IAQ 2010.

Air samples were collected on appropriate culture media — tryptic soy agar for bacterial enumeration and Sabouraud dextrose agar or malt extract agar for fungal enumeration. After incubation under standard conditions, colony-forming units (CFU) were counted and expressed as CFU per cubic metre of air (CFU/m³). Concurrent measurements of environmental parameters — including temperature, relative humidity, and air velocity — were recorded at each sampling location to enable correlation analysis between physical conditions and microbial concentrations.

Microbial Concentrations and Species Composition

Airborne bacterial concentrations varied substantially across sampling locations, with higher counts generally observed in spaces with greater occupant density and less effective ventilation. Lecture halls during occupied periods showed among the highest bacterial concentrations, consistent with the well-established relationship between human occupancy and indoor bioaerosol levels. The predominant bacterial taxa identified in indoor air samples were Gram-positive cocci and rods — including Micrococcus, Staphylococcus, Bacillus, and Corynebacterium species — all of which are commonly associated with human skin, oral, and respiratory microbiota.

Fungal concentrations were also variable across locations, with moisture-prone areas and spaces adjacent to outdoor environments tending to show higher fungal loads. Common indoor fungal genera identified included Aspergillus, Penicillium, and Cladosporium — ubiquitous environmental fungi that are also among the most common causes of allergic sensitisation and respiratory symptoms in susceptible individuals.

Environmental Parameter Correlations

Analysis of the relationships between environmental parameters and microbial concentrations revealed several significant associations. Relative humidity showed a positive correlation with fungal concentrations, consistent with the well-established requirement of fungi for moisture to support growth and sporulation. Temperature also showed associations with microbial levels, though the relationship was more complex and influenced by the interaction between outdoor conditions and air-conditioning system performance.

Occupant density emerged as one of the strongest predictors of bacterial concentrations, reflecting the direct contribution of human occupants as sources of airborne bacteria. Spaces with higher air exchange rates and better ventilation generally showed lower microbial concentrations, highlighting the importance of adequate ventilation design and maintenance in controlling indoor bioaerosol levels.

Regulatory Compliance

When compared against the acceptable limits specified in the Malaysian ICOP IAQ 2010, some sampling locations exceeded recommended thresholds for total bacterial and/or fungal counts. These exceedances were most commonly observed in densely occupied spaces with suboptimal ventilation — a finding that is consistent with international IAQ monitoring studies in educational facilities. The identification of non-compliant locations provides actionable information for building management, enabling targeted interventions such as enhanced ventilation, improved air-conditioning system maintenance, cleaning protocol modifications, and occupancy management strategies.

Public Health Implications

Poor indoor air quality in educational institutions can contribute to a range of health effects among students and staff, including respiratory infections, allergic reactions, headache, fatigue, and reduced cognitive performance. In a tropical country like Malaysia, where buildings are sealed against outdoor heat and humidity and rely extensively on recirculated air-conditioned environments, the maintenance of acceptable indoor microbial loads requires deliberate attention to ventilation system design, filter maintenance, moisture control, and cleaning practices.

The findings of this study support the need for regular IAQ monitoring in Malaysian educational institutions, with particular attention to densely occupied spaces. Integration of IAQ considerations into building design standards, maintenance protocols, and institutional health and safety policies would help ensure that learning environments support rather than compromise the health of their occupants.

Limitations

The study was conducted at a single university, limiting the generalisability of findings to other educational institutions with different building designs, ventilation systems, and occupancy patterns. Culture-based air sampling methods detect only viable, culturable microorganisms and may underestimate total microbial diversity. Seasonal variation in microbial concentrations was not assessed. The health effects of the observed microbial exposures were not evaluated directly in the study population. Future research should employ molecular-based methods alongside culture-based approaches to provide a more comprehensive characterisation of indoor air microbiota.

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