Comparing mould levels in the UK and Denmark

Testing dust or air sampled from buildings has become an important tool for revealing hidden mould and damp problems and for ensuring that a safe and healthy level of indoor air quality is maintained..

However, indoor dust and air will always contain mould spores from the outdoor air. Simply quantifying total mould levels in a sample will therefore not reveal whether the mould found in the samples originates from mould growing indoors or reflects natural background levels of mould originating in the outdoor air.

To distinguish between microorganisms originating from indoor microbial sources and spores that accumulate in the dust from the outdoor air, one needs to compare the species composition and quantity of mould material in a given sample with information from a database about relevant moulds and bacteria species from air and dust samples.

Geography matters

HouseTest’s DNA analysis was originally based on a Scandinavian database, but as the distribution of bacteria and fungi differs geographically in the outdoor air it limits the geographical area where it can be used.

Knowledge of the local microbial composition in any potential area is thus necessary to determine whether the microorganisms identified in a sample are a natural part of the local microbiome or a sign of a building infestation. We therefore engaged in a project to determine if the levels of mould and bacteria differ between UK and Danish sampling sites to expand the geographical area where the method can be used. Over a period of 19 months, samples were collected throughout the UK, analysed for 24 species or groups of moulds, bacteria and plant pollen, and compared to results from samples collected in Denmark.

The local microbiome in the UK

The results showed that the overall picture fits well with data previously collected from Scandinavian sampling sites: warmer regions show higher outdoor mould levels, and they appear earlier compared to colder regions. Importantly, the same species dominate the outdoor air, and the ratio between them is fairly constant.

Thus, samples from both the UK and Danish sites found highest levels of Cladosporium herbarum with lower levels of Cladosporium cladosporides which in turn were higher than Cladosporium sphaerospermum which again was higher than Aspergillus versicolor.

In conjunction with previous studies showing that the species composition from indoor air of damp buildings was similar in UK and Scandinavia, this project confirms that the HousTest's qPCR test for mould can be used in the UK, provided that the algorithm developed to distinguish between profiles from mouldy building to those from dry buildings is modified according to the newly gained insights