Fungi that trigger allergies go under scrutiny.
Industry researchers have produced the largest study yet of airborne fungi in US buildings. The fungal fingerprints may help scientists understand their role in triggering allergies and other medical conditions.
Exposure to spores released by moulds is known to cause or worsen allergies and trigger asthma episodes in sufferers. Spores enter buildings through air ducts or open windows and can thrive in moist indoor conditions.
Brian Shelton and his colleagues at the microbiology laboratory PathCon in Norcross, Georgia, found Stachybotrys chartarum, a fungi thought to be toxic, in 6% of indoor air and in 1% of the outdoor air from buildings surveyedsup>1
"Finding some of these organisms is not uncommon," says Shelton. He hopes the study will provide baseline figures on the natural occurrence of fungi. This could be of use in future studies on the health effects of particular species.
"The list of identified fungal species is certainly a contribution to science," says David Miller, who studies allergens at Carleton University in Canada. But he cautions against extrapolating detectable quantities of fungi to an individuals exposure level.
Isolation of the mould does not necessarily indicate exposure to toxins that they produce. It is not known whether spores produce toxins as the mould does, or exactly what their health effects are, Shelton says.
Other rare health effects, such as bleeding lungs, have been attributed to Stachybotrys chartarum - dubbed toxic mould. But the link is disputed: "There is no good evidence that mould in indoor environments is a significant health problem other than being a potential cause of allergy and asthma," says Richard Wasserman, allergist and spokesman for the American Academy of Allergy, Asthma, and Immunology.
The controversy is, however, highlighting mould-related heath issues. "Mould is replacing asbestos as the next issue for industrial hygiene," says Henry Lick, president of the American Industrial Hygiene Association.
The PathCon lab received over 12,000 samples during air-quality investigations in 1996 to 1998 - primarily from indoor samples of 1,700 buildings across the United States. This allowed it to provide detailed lists and concentrations of fungi for individual regions, including moulds.
The survey measured culturable fungi, which are those that can be isolated on specially designed laboratory media. Even though cultures provide the best available measures, they are subject to limitations because not all fungi can be grown in this way.
"The number of viable spores detected by this method is extremely low," says Miller. Shelton counters that those that cant grow on culture arent of concern in buildings.
A National Academy of Sciences report in 2000, called Clearing the Air, identified a need for a standardized method, other than culturable fungi, to document exposure to fungal allergens.
The authors concede that this is primarily a descriptive study. However, it provides profiles that would probably not come from any other source, given the cost and logistics involved in collecting samples.
- Shelton, B.G. Kirkland, K.H. Flanders, W.D. Morris, G.K. Profiles of airborne fungi in buildings and outdoor environments in the United States. Applied and Environmental Microbiology, 68, 1743 - 1753, (2002).
VIRGINIA GEWIN | © Nature News Service