Background. Energy-efficient buildings may have inadequate ventilation which increases the risk of mold problems, due to an increased humidity. Several laboratory and field studies have demonstrated that the enzyme β-N-acetylhexosaminidase (NAHA) is a good marker of fungal cell biomass. The purpose of the study was to further extend measurements of NAHA in buildings with and without humidity problems.

Material and methods. Air samples were taken in buildings with or without suspect mold growth. 300 L air was sucked though a preloaded filter (0.8 m pore size) or a cyclone sampler. After sampling, an enzyme activator was added to the filter, followed by a developer. The fluid was sucked through the filter and the fluorescence was read, expressed as the NAHA enzyme activity in units (U/ m³). The buildings were inspected for the presence of fungal growth or odours indicating fungal growth.

Results. NAHA values in rooms with fungal growth were significantly higher than in clean rooms (p= 0.001). Fungal spore fractions comprised about 40 % of the total fungal biomass. NAHA measurements could be used to monitor the effect of movements in the sampled room
and of cleaning.

Comments. Enzyme measurements of fungal biomass are rapid and easy to perform. As with all measurements the limitation is conditions at the moment of measurement. The sensitivity and specificity of the method is high which makes it suitable for field use. Incorporation of the small fractions in assessment of fungi is important as this fraction has a higher penetration rate into the deep parts of the lung and is hence important to include for proper risk assessment.