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Penicillium species are very common moulds. About 200 species have been described. They are commonly called the blue or green moulds because they produce enormous quantities of greenish, bluish or yellowish spores which give them their characteristic colours. Their spores are found everywhere in the air and soil. They are the most common causes of spoilage of fruits and vegetables. For example, Penicillium italicum and Penicillium digitatum are common causes of rot of citrus fruits, while Penicillium expansum is known to spoil apples. Most species are active producer of toxins.
The most common Penicillium species in indoor environment is Penicillium chrysogenum. It is widespread and has a wide range of habitats. In indoor environment, it is extremely common on damp building materials, walls and wallpaper, floor, carpet mattress and upholstered furniture dust. It produces a number of toxins of moderate toxicity. It is allergenic and can infect immuno-compromised patients.
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They say “the dose makes the poison”. But what’s the dose for indoor mould? Currently there is no answer to this question. Determining this dose would be a difficult task for a number of reasons:
- There are several species of moulds with differing health effects.
- People are not just exposed to mould but also to other environmental pollutants including bacteria, protozoa, dust mites and non-biological compounds.
- Some people are highly sensitive to mould even at concentration levels that may be considered ‘normal’.
It is generally accepted that no amount of mould should be allowed in occupied dwellings. However, it is impractical to get rid of all the mould in a building. A number of organisations have provided some guidelines in the past on what levels of mould would be considered a problem in occupied dwellings. But none of these guidelines have been accepted widely and some have even been dropped as more information concerning indoor mould became available. Below is a summary of some of these guidelines.
In 1989, the American Conference of Governmental Industrial Hygienists (ACGIH®) had considered fewer than 100 colony forming units per cubic meter of air (CFU/m3) as of no concern. For duct insulation, the Department of Environmental Health and Safety (DEHS) of the University of Minnesota, considers 10,000 CFU/gram as low, 10,000 to 100,000 CFU/gram as medium, 100,000 to 1,000,000 CFU/gram as medium to heavy and > 1,000,000 as heavy contamination. The Health Canada Technical Guide, 1993, states that if more than 50 CFU/m3, of the same species other than Cladosporium or Alternaria were detected in indoor air, there may be reason for concern. It also states that up to 150 CFU/m3 would be acceptable if there was a mixture of species reflective of outdoor air. Also, up to 500 CFU/m3 would be acceptable in the summer, if the species present were primarily Cladosporium.
There are other guidelines. The German Federal Environmental Agency (Umweltbundesamt, 2002) has probably the most comprehensive guidelines. Unfortunately the guide is only available in German language.
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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.
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Hazard classes of indoor mould
Indoor moulds have been grouped into 3 hazard classes based on associated health risk. These classes are similar to risk groups assigned to micro-organisms handled in laboratory environments.
- Hazard Class A: includes fungi or their metabolic products that are highly hazardous to health. These fungi or metabolites should not be present in occupied dwellings. Presence of these fungi in occupied building requires immediate attention.
- Hazard class B: includes those fungi which may cause allergic reactions to occupants if present indoors over a long period.
- Hazard Class C: includes fungi not known to be a hazard to health. Growth of these fungi indoors, however, may cause economic damage and therefore should not be allowed.
Health Problems Associated With Indoor Moulds
Exposure to indoor mould has been associated with the following health problems:
- Lower respiratory symptoms such as coughing and wheezing;
- Respiratory infections such as aspergillosis;
- Allergic diseases, including allergic asthma and bronchitis;
- Non-inflammatory, unspecific symptoms, such as eye and skin irritation, fatigue, headache, nausea, and vomiting.
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