Abstract
Indoor fungi are increasingly recognised to be associated with adverse respiratory health effects. However, how fungal exposure should be measured remains a complex issue. New Zealand has particularly high rates of respiratory illness, and also poor insulation and housing, which might contribute to high levels of indoor fungi. The extent to which indoor fungi contribute to asthma exacerbation and development in New Zealand children has yet to be characterised. This thesis therefore aimed to:
1. Determine the levels, genera and seasonality of fungi in homes in New Zealand.
2. To establish whether indoor fungal air or dust samples were more advantageous to measure inhalation exposure, and whether measurement methods correlate.
3. To explore the potential aerosolisation and inhalation risk of fungal materials from carpet and hard flooring.
4. To determine whether there was evidence of an association between indoor fungi and health effects in New Zealand children.
Mean levels and genera of viable and total fungi in indoor and outdoor air, and viable fungi and ergosterol in indoor flooring dust were established in an intensive study of 20 homes over four seasons, the first such study carried out in New Zealand (Aim 1). As observed in overseas studies of temperate climates, Cladosporium and Penicillium were found to dominate air samples. Genera of viable fungi in flooring dust samples had a wider range of fungal diversity, as measured using Recognisable Taxonomic Units, than viable fungi in air samples, with less dominance of a single genus, and a greater abundance of yeasts, Aureobasidium, and pycnidial groups (Aim 2). Notably, none of the four methods used to measure fungi (viable spores in air, total spores in air, viable spores in dust, ergosterol in dust), were found to correlate with each other, suggesting that the various methods chosen represent unique and separate exposure measures of indoor fungi (Aim 2).
Experiments conducted to examine where fungal material is found in carpeting, determined that betaglucan (a biomass marker of fungi) is found throughout the carpet pile, and does not just remain on the surface of the carpet after deposition from the air (Aim 2). Aerosolisation experiments from flooring should attempt to replicate the vertical distribution of fungal material, rather than assume contaminants remain on the surface of the flooring. An embedding process was developed to distribute the dust and fungal spores in carpet to replicate this distribution. A comparison of concentrations of PM 2.5 dust particles was conducted above vinyl hard flooring, and cut and loop pile nylon carpets, seeded with varying amounts of dust, in a purpose built disturbance chamber, to examine the potential for aerosolisation of dust from flooring. Flooring type and carpet construction were both found to influence aerosolisation rates of PM2.5 (Aim 3). Highest rates of aerosolisation occurred on hard flooring at 1 g/m2 and 3 g/m2 dust seeding rates, followed by cut pile, then loop pile, carpet at 75 g/m2. Almost no aerosolisation occurred on cut and loop pile carpet seeded with low levels of dust (3 g/m2). This indicates that dust may be readily aerosolised from hard floor surfaces, but does not appear to do so from carpeted surfaces (Aim 3). Differences in aerosolisation rates of six types of fungal spores were also examined. Differences in aerosolisation rates were again found between flooring types, and between spore types (Aim 3). Like PM2.5, almost all spores were more readily aerosolised from hard flooring than from carpeted flooring. A notable exception was that larger Alternaria spores were disturbed in equal levels from both carpet and hard flooring, although low quantities were disturbed when compared to the various Penicillium spores.
Evidence of an association between indoor fungi and health effects in New Zealand children were investigated in three separate studies (Aim 4). Statistically significant links were observed in univariate analysis between self reported and researcher reported mould and an increased prevalence of colds, chest infections and cough in children from the New Zealand Allergy and Asthma Cohort Study at age 3 months and 15 months (P≤0.05). Some mould assessments were also positively associated with an increased incidence of wheeze and asthma in children, including researcher observed smell of mould at 3 months and current asthma and wheeze at 15 months, parentally observed dampness at 15 months and current asthma and wheeze at 15 months, and parentally observed visible mould at 15 months and wheeze at 15 months (P≤0.05). Betaglucan levels (µg/m²) in bedroom flooring at 3 months were significantly related to colds, chest infections and cough at 3 months, and to chest infections, wheeze and atopy at 15 months (P≤0.05). This is the first study to observe a link between increased betaglucan levels in flooring dust and wheezing in young children.
In a study of 450 children in the Wellington region, higher levels of visible mould were observed in the bedrooms of new onset wheezing children than those with no wheezing history (P≤0.05), when examined by parents and researchers (Aim 4). A mould severity scale show card was designed to allow a semi-quantitative measure of mould severity for each bedroom. Both the parental and researcher observed mould severity scores were significantly associated with new onset wheezing status (P≤0.05). Smell of mould was also closely associated with wheezing status, followed by visible mould presence on the curtains (P≤0.05). Both parental and researcher observed mould severity scores were positively associated with average bedroom temperature and humidity (P≤0.05), with colder damper bedrooms more likely to have a higher level of mould, and mould in more than one location, than warmer drier bedrooms.
Bedroom levels of airborne fungi were compared in a pilot study of 20 children with severe asthma and 20 age, gender and area matched control children with no asthma or wheezing history (Aim 4). Several fungal measurement methods were used, including traditional short sampling of viable spores and total spores, and a new method of measuring long term exposure – the electrostatic dust cloth. The static dust cloth was placed in homes for four weeks to measure airborne levels of fungi using fungal DNA and ergosterol. The results of the study indicate that fungal levels in the bedrooms of children with severe asthma were no different to those in control children’s bedrooms, irrespective of the method used to quantify fungi (P>0.05). This implies that current airborne fungal levels in the bedroom do not contribute to severe asthma, at least in this small pilot study. When comparing methods, two correlations were found for measures of fungi in indoor air; viable spores were found to correlate to levels of DNA on static cloths and total spores were found to correlate to levels of ergosterol on cloths (Aim 2). Viable spores did not correlate with total spores in indoor air samples but did correlate with total spores in outdoor air samples. This pilot study indicates that longer term measures of fungal levels in airborne dust using static cloths is possible and may provide a link between viable and total spores (Aim 2). This new technique may prove a useful additional method of collecting indoor fungi.
Measurement of indoor fungi remains a complex issue. However, this thesis makes a significant contribution to our understanding of fungal spore aerosolisation from flooring, and the question of whether flooring dust samples are representative of inhalation exposure. This thesis has also demonstrated that careful attention should be given to how well different methods to quantify fungi predict inhalation exposure. Adverse health associations with fungi, such as those observed in this thesis, can only be unequivocally confirmed or refuted when independent and accurate inhalation exposure measures are found.