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Sampling for Airborne Mould: When Should One Use Viable, Non-viable or Both Methods?

An air quality investigation may require determining airborne mould (spores and hyphal fragments) concentration. Air can either be sampled onto some growth media for culture analysis or on a sticky surface or a filter membrane for direct microscopic examination. It is sometimes debated as to whether one should take non-viable samples, viable samples or a combination of the two. Either method can be used without the other or both can be used together (at the same time) depending on the objectives of the investigation.

Due to lack of standardization some terminologies used in air sampling are technically incorrect or misleading. Let’s discuss these terms first.

Non-viable Air Samples
“Non-viable air samples” refer to samples that are taken on some sticky media or on a filter membrane or tape and subsequently examined directly under a microscope for enumeration and identification of mould spores and hyphal fragments without culturing. In other words, the samples are taken for analyses by direct microscopic examination (DME). Results are presented as a listing of various categories of moulds and the corresponding number of spores or hyphal fragments per cubic meter of air (Spores/m3). This term is technically inaccurate since viable and non-viable propagules are indistinguishable under the microscope and hence both are enumerated.

Viable Air Samples
“Viable air samples” refer to samples that are taken on some growth media and subsequently incubated for mould propagules (spores and/or hyphal fragments) to germinate and form colonies. The resulting colonies are then enumerated and/or transferred to other media for identification to genus or species. Results are presented as a listing of the recovered moulds and their corresponding number of colony forming units per cubic meter of air (CFU/m3). That is, the analysis of viable air samples involves culturing. The term is also technically inaccurate because some (sometimes most) of the propagules impacted on the growth media may not germinate not because they are not viable but because of the selectivity of the growth media used, competition from fast growing moulds or that some moulds can only grow on living hosts.

Spore traps
“Spore traps” is commonly used to refer to non-viable air samples. However, whether sampling is done for culture analysis with an RCS, Andersen or for DME with Air-O-Cell or other similar cassettes it involves spore trapping. “Spore traps” is therefore applicable to both viable and non-viable samples.

When should one use viable, non-viable or both sampling methods?

The easiest way to decide on this is first to define the objectives of air sampling, data required from sample analysis and the questions these data are meant to answer. The objective might be broad or very specific.

  • When to use non-viable sampling

If the objective of air sampling was to have an idea of how contaminated the air is, then the data required would be total counts. Non-viable samples would then be the best to take because counting includes both those propagules that can grow on laboratory media and those which cannot grow either because they are dead or would not grow on the selected media. Non-viable sampling may also be selected when the objective of air sampling is to determine the total counts for airborne spores prior to and after remediation to assess the effectiveness of remediation. In this case viable air samples would not be necessary.

  • When to use viable sampling

If the objective of air sampling was to find whether the air contains a specific species of mould e.g., Aspergillus fumigatus, then identification to species would be required. Since non-viable analysis would not distinguish A. fumigatus from other Aspergillus species and not even from Penicillium species and related genera, then sampling for viable analysis would be selected. For detecting a specific species, a selective media that would support the growth of the mould of interest would also be selected. If identification to species was required for a broad range of moulds, then media that support growth of a wide range of moulds would be selected.

  • When to use both non-viable and viable sampling

If the objective of air sampling was to determine the total airborne mould concentration and at the same time determine the proportion of viable propagules, then both sampling methods would be used. This would possibly be the case in hospitals where concern is not only the total concentration of airborne mould but also the viable species present.

Conclusion
These are not the only reasons why one may sample for non-viable, viable or both non-viable and viable analysis. It all depends on the objectives of air sampling, the data required and the questions these data are intended to answer. Read Interpreting Numerical Data of Viable Airborne Mould Samples and Guidelines for Interpreting Numerical Data of Non-viable (Spore Traps) and Viable Airborne Mould Samples.

To get hands-on experience on the application of these guidelines register for our Mould Training Seminars today!

Do you have a question on mould? Send it to us at Contact US.

Cryptococcus gattii: What is It?

An alert has been issued on the spreading of Cryptococcus gattii from the Vancouver Island to Mainland British Columbia (CBC News, Friday, June 03). What is this Cryptococcus gattii? It is a yeast-like fungus belonging to a group of fungi called Basidiomycetes (where mushrooms also belong!). This fungus was thought to have a restricted geographic distribution in the tropics and subtropics. It is has been reported in Australia, Papua New Guinea, parts of Africa, the Mediterranean region, India, south-east Asia, Mexico, Brazil, Paraguay and Southern California. The BC report was the first outside the tropics and subtropics.

Cryptococcus gattii has an unusual association with trees. In Australia it is associated with some Eucalyptus trees. In British Columbia, however, Cryptococcus gattii has been recovered from multiple species of native trees, but not from any of the introduced Eucalyptus species. It has been isolated from soil, barks of trees and from the air.

Unlike indoor moulds and yeasts, Cryptococcus gattii is a true pathogen and therefore can infect even healthy people. It has a preference for respiratory and nervous systems of humans and animals. Exposure to humans is mainly through inhalation of airborne spores into the lungs.

Should you have a question on mould, send it to us at My Question.

Airborne Mould Spores: Could They Be Dangerous To Health?

Mould spores are tiny structures produced by moulds for reproduction purposes. They are so small that we can hardly see some of them even when magnified 400 times. One cubic meter of outdoor air may contain as many as 1,000,000 spores. The volume of air we inhale at rest is estimated at 10 litres per minute. Therefore, in an hour we inhale close to 600,000 spores. The air in some working environments including mouldy buildings may contain up to 1,000,000,000 spores per cubic meter of air.

In indoor environments moulds grow on moist surfaces such as the drywall, wallpaper, carpet, baseboards, and heating, ventilation and air-conditioning systems (HVACs). As these moulds grow, a stage is reached when they produce spores. The spores become airborne after drying out or if disturbed.

Could airborne spores be dangerous to our health?
About 20% of the population is allergic to mould spores. Apart from being allergenic, spores of some mould species such as Stachybotrys contain toxic compounds called mycotoxins. Symptoms associated with mould spores may include allergy, headache and fatigue, running nose, sneezing, coughing, pneumonia and Asthma among other non-specific symptoms. Young children, the elderly and people undergoing medical treatment are particularly susceptible to mould spores.

How can we control indoor mould spores?
It is extremely difficult to get rid of spores completely. We can, however, reduce their numbers by controlling mould growth in our houses or offices. Mould growth is associated with moisture problem as a result of flooding, leaks in roofs or plumbing and condensation in case of poor ventilation or inadequate insulation. The key to controlling mould growth is keeping our houses or offices dry by maintaining low relative humidity (below 70%) thus eliminating or slowing the growth of most mould species. Any water leakage should be repaired immediately and the water dried out within 48 hours. Constant monitoring for mould growth in the kitchen, bathrooms, window frames, carpets and baseboards is recommended. The earlier the mould is discovered the cheaper and easier it is to get rid of the problem.

What should you do if you notice mould growing in your house or office?
Do not panic! Seek professional advice. Not all moulds are dangerous to health, but no mould should be allowed to grow in our dwellings. Also the health effects of indoor moulds depend on the amount of mould one has been exposed to, length of time of exposure, the types of moulds present and individual’s resistance. Therefore, presence of mould does not necessarily mean the occupants have been affected.

Which are the most dangerous moulds?
People have come to believe that black moulds are the most dangerous.
The truth is, colour does not determine whether a mould is of health concern or not. To know whether a mould is dangerous or not requires the mould to be identified by a qualified mycologist.

Should you have a question concerning moulds, please send your question to us at My Question.

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