City air to go under microscope

Steve Pointing says Auckland needs to know what parts of its dust are potentially harmful. Photo / Sarah Ivey

Researchers hunting down dust microbes in Auckland to better understand fallout of increasing urbanisation

Does working in a high-rise building or spending a lot of time downtown expose you more to dust-borne bugs?

AUT University scientists will for the first time measure what microbial allergens Aucklanders come into contact with every day in a study to provide insights for health authorities and city planners.

Microbes are everywhere, but urban development and increased human occupation can affect the numbers and types of microbes we are exposed to.

Common symptoms of microbial allergens include headache, dry cough, throat and nasal irritation and fatigue, but some can cause disease.

A joint study, led by Professor Steve Pointing of AUT's Institute for Applied Ecology and in collaboration with US-based Duke University's Global Health Institute, seeks to understand the effects of urbanisation on their prevalence.

Allergens could take the form of anything, from food to pollen from trees, Professor Pointing told the Herald.

"But one class of allergens that is really under-appreciated is microbial allergens, compounds that come from the dead cell walls of bacteria and fungi, and basically form a large component of dust."

It was estimated as much as 60 per cent of dust consisted of dead microbial cells, and Auckland was considered a very dusty city.

"We are a large city surrounded by a lot of natural areas that are conducive to dust formation - large tidal flats and agricultural areas - and we get a lot of dust here anyway."

The changing land use in the city was also driving up dust levels.

"High rise buildings, construction, the use of ducted air conditioning, all of these things increase dust loading, so if we are being responsible urban citizens, we need to find out what parts of the dust are potentially harmful."

A World Health Organisation working group on allergies recognised that microbial growth leading to greater endotoxin and beta-glucan levels was a potential health hazard.

The WHO estimated between 10 and 50 per cent of buildings in Australasia were susceptible to conditions that promote microbial growth and allergen production.

But little is known about levels in this country, or their role in occupational and domestic allergen exposure.

Professor Pointing said high-rise buildings could be hot-spots because of a high density of people within them and most such buildings were centrally air-conditioned.

"It's almost as though they act as a reservoir for microbes."

To gauge levels, the researchers will set up across the city high-tech pumps capable of sucking thousands of litres of air each minute, and analyse what microbes they collect.

"We want to be able to deliver a predictive tool for use by the council and other organisations, telling them these are the ranges and patterns we can expect."

Microbes are everywhere

* Dust microbes, found on the street, in your home or in air conditioning units, are the source of allergens that come in two forms.

* Bacterial allergens are mainly endotoxins, which can be highly allergenic in the respiratory tract and can also cause intestinal tract problems, while fungal allergens are mainly beta-glucans, a type of sugar polymer.

* Pathogenic bacteria account for about 0.5 per cent of urban airborne microbes, and pathogenic fungi about 1 per cent.

* Microbial allergen levels rise with increasing human habitation, and probably account for a significant portion of unexplained allergies in humans.