Indoor Microbiological Contaminants in Residential Homes in Spain

The indoor microbiological contaminants present in the built environment, including residential buildings, can pose significant risks to human health and well-being and the sustainability of indoor environments. Therefore, the total aerobic microbial count (TAMC) and total yeast and mold count (TYMC) are key indicators used to evaluate microbial contamination levels in indoor spaces. This study presents an assessment of TAMC and TYMC in residential indoor environments in two cities in Spain, Pamplona and Seville, which represent different climate zones, with Seville characterized by extensive air conditioning use due to its high summer temperatures. We conducted sampling and analysis in 20 dwellings over two summer campaigns to quantify microbial populations and identify parameters that worsen TAMC and TYMC and promote amplification (I/O, indoor/outdoor). The results show that ventilation type, building design, and climatic conditions significantly influence indoor bacterial amplification. The study indicates that the implementation of the Spanish building code in 2006 has improved microbial Indoor Air Quality (IAQ), even in airtight and energy-efficient dwellings, highlighting the importance of integrating ventilation and health considerations into sustainable building design. Environmental parameters such as temperature and CO 2 concentration were reliable indicators of bacterial proliferation. Kitchen design and the presence of pets also emerged as relevant determinants of microbial loads. Overall, the use of I/O ratios proved effective for identifying indoor microbial amplification, supporting their application in future IAQ assessments, sustainable building evaluations, and healthy housing strategies.