OUTDOOR SPORE COUNTS ARE OFTEN HIGHER THAN THOSE INDOORS. DO THESE OUTDOOR SPORES HAVE HUMAN HEALTH EFFECTS?
Yes, they do. Several papers in the literature document the relationship between asthma outbreaks and especially high concentrations of specific spore types. “New Orleans Asthma” is a syndrome blamed on basidiospores. Thunderstorm asthma has been blamed on a particular type of ascospore. In addition, clear relationships have been found between increased hospital admissions for asthma and outdoor spore concentrations. In the American Southwest, outdoor Alternaria exposure may actually initiate asthma in children.
None of this is surprising. Indoor fungi are simply those outdoor fungi that have found a food source indoors. All the indoor fungi are also present outdoors, often in concentrations higher than commonly found indoors. This means that the fungal agents of disease are also outdoors – allergens, toxins, glucans, chitin, etc. Even volatile organic compounds can be detected in outdoor air, especially clean country air.
Obviously, some kinds of fungi can become greatly amplified indoors. In New Orleans, wet wallboard became infested with Aspergillus and Penicillium species so that spore concentrations in houses were higher even than those outdoors (exceeding 106/m3). The same thing happens when wet or damp houses are closed for weeks or months. As long as water is there, certain molds will grow and conditions will become worse, at least with respect to one or two kinds of fungi, than those outdoors.
Generally, however, these are not the conditions under which most non-specific health effects blamed on fungi are found. Usually, someone will detect a “moldy” odor or see a stained ceiling tile or perhaps see mold growing in some isolated spot in their environment. Especially if they have no immediate control over their environment (e.g., in an office environment), the observation may lead to worry and concern that health effects may occur. This concern is often followed by symptoms.
However, if these same conditions are observed in a home, especially an old one in which contractors have not recently been involved, the problem is remedied and no symptoms occur. Also, the same fungi found under these conditions (Penicillium, Aspergillus, Cladosporium) are probably at least as abundant in the outdoor air as they are on the inside.
Also consider the fact that gardening is considered to be a healthy form of exercise. You are outdoors breathing the “fresh” air (assuming you don’t live in the Los Angeles basin!) and are encouraging things to grow. You happily pull weeds and dig holes for the plants, breathing in the wonderful odors of the microbial volatiles responsible for the odor of new-turned soil along with all the spores (including those of Stachybotrys) that are growing on the dead leaves you are digging up.
Obviously, there are people who cannot enjoy these activities. If you have severe mold-related asthma or hypersensitivity pneumonitis related to Aspergillus or actinomycete exposure, you will not be comfortable. On the other hand, gardening has never been reported to cause “toxic” symptoms such as headache, fatigue (other than that induced by using your muscles), memory loss, etc.
Finally, people whose occupations give them opportunities to work outdoors often experience much higher spore concentrations than would be found in the vast majority of interior situations. Sawing wood, working with municipal compost, moving stored lumber around, harvesting grain, sweeping the streets – the list is endless – all lead to spore exposures that can be orders of magnitude above that experienced by office workers living with moldy ceiling tiles or homeowners with a leaky bathroom sink.
Dr. Harriet Burge is director of aerobiology at EMLab P&K and associate professor and director of the microbiology laboratory at Harvard School of Public Health. Widely considered the leading expert in IAQ, Dr. Burge pioneered the field more than 30 years ago. She has served as a member of three National Academy of Sciences committees for IAQ, including as vice chair of the Committee on the Health Effects of Indoor Allergens.
To submit a question to Dr. Burge, write to her by e-mail at askdrburge@emlab.com. All questions posed to her will receive a reply, although space limitations prevent us from publishing them all. By submitting, you agree that your question and Dr. Burge’s answer may be published in a future edition of IE Connections.
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