Identifying moulds in homes

Humid air or condensation is one of the most significant contributors to dampness in homes. Moisture not only can damage the structure of homes, but it can also promote the growth of mould. Mould has been linked to various health issues such as allergies, asthma and sick building syndromes. Therefore, having drier houses also means healthier homes.

The most effective method to reduce dampness is by creating ventilation in homes. It includes opening windows and doors to get airflow between indoors and out. Alternatively, home ventilation systems (HVS) achieve similar movement by blowing dry air indoors from the roof spaces in houses. 

But how effective is an HVS in really removing dampness in houses? The AMSRC lab is leading a research study looking into the effect of an HVS on mould growth in homes. This research is part of a larger project investigating the impact of HVS on indoor air quality led by Associate Professor Teri-Ann Berry and her IAQ Research Team. Using a molecular genetics approach, we can identify the species composition and amount of mould growth in homes to detect changes in mould presence following the installation of HVS. All we need are samples of surface swabs, dust or air from houses.

How do we identify mould species? We use Next Generation Sequencing, which enables us to target specific regions of mould DNA and to sequence the DNA from multiple species all at once. We will then identify species using global genetic databases. Currently, there is not much knowledge on the diversity of mould species found in New Zealand homes. This study will obtain some baseline information on moulds and potentially identify important species that may be linked to human health issues or ones associated with water damage in buildings in New Zealand.

How do we quantify the amount of mould? We use real-time PCR (similar equipment to that being used to detect COVID-19), which can estimate the amount of mould DNA in the sampled environment. Quantity of DNA is usually used as a proxy for estimating the amount or number of organisms present – more DNA detected suggests more mould in the environment. Here, we will quantify specific moulds of potential health concern (e.g. AspergillusPenicilliumStachybotrys) and the overall mould DNA present in the sampled environment before and after installation of the HVS. If the HVS is able to suppress moulds’ growth and production, we would see overall mould DNA to be significantly less post-installation. A significant reduction in mould would suggest that the HVS may effectively prevent or reduce human health issues associated with damp housing.

In a pilot study last year, we collected swab and dust samples from different rooms in a single house before and after the installation of an HVS. We wanted to identify the types of mould found in the home and if species diversity changes after installing an HVS. Here, we first cultured the samples to isolate pure mould species before sequencing their DNA. We found that each room had different types of mould species, and it varied after the installation of an HVS. In particular, the number of species in the bathroom significantly dropped post-installation. We detected various airborne moulds and mould species brought into the house by the occupants (e.g. on shoes, bags, clothes). We found some moulds associated with humidity (e.g. Cladosporium spp.) and potentially pathogenic to humans (e.g. Penicillium spp., Rhodotorula spp.) and sheep (Pithomyces chartarum)! The  latter, we suspect, was either wind-blown or brought in by the occupants from outdoors.

This year, we will continue with the main study, which involves sampling from various homes from two cities in New Zealand. Our research will feedback to the larger multidisciplinary project (engineering: air quality and social sciences: lifestyle) to provide a more complete and meaningful picture on maintaining healthy homes in New Zealand.

Dr Marleen Baling

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