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Tuesday, 20 March 2012

Mould: Much maligned, misinterpreted and far too often missed mediator of malaise

Mould – the word engenders images of slimy growths on old bread and cheese.  It stimulates revulsion and the immediate reaction to discard food as having gone bad.  Do these microscopic creatures that form vibrant colonies deserve such a tainted reputation.

Some moulds are beneficial like the penicillin producing species and those used in producing cheeses, sake, soy sauce, salami and other foodstuffs. Others are known for their association with illness; alfatoxins and liver cancers; ergots which were implicated in the psychiatric manifestations associated with the Salem witches and several others that are specific nephrotoxins or neurotoxins.  However saying that moulds are bad is like saying all bacteria are bad.   We just need to know our moulds better, and given there are thousands of them, our general knowledge is limited.

Considerable attention has been drawn to the issue of moulds in housing, but perhaps not the concerted attention of public health authorities – in part likely because it affects such a large proportion of the population

Moulds received considerable attention in the ‘90s in what is actually a public health myth. “Toxic mould” – Stachybotrys chartarum,   the nickname was the result of an investigation of pulmonary hemorrhage in infants.   In 2000 CDC reevaluted the original investigation and raised questions about whether such an association existed MMWR March 9 2000.  In essence the retraction of the widely disseminated and well entrenched “knowledge” that moulds could cause death in particular circumstances.  What a great public health controversy given millions spent in remediation and the continued propagation of the fallacy that Stachybotrys chartarum was associated with a severe allergic response that could result in death.  

Not to belittle the problems with mould and housing which is our focus of attention.

Moulds produce spores.  Spores can produce an inflammatory response when inhaled.   The extent of the inflammatory response is in part correlated with the burden of spores inhaled.   Inflammation can be manifest in eye, nose, throat, bronchial and pulmonary irritation.  More simply put, some cold symptoms and the potential for exacerbating asthma.  The following table gives some sense of the expected relative risk for symptoms in persons living in damp and/or mouldy housing

OR (95% confidence interval)
Upper respiratory tract symptoms
1.70 (1.44-2.00)
1.67 (1.49-1.86)
1.50 (1.38-1.64)
Current asthma 
1.56 (1.30-1.86)
Ever diagnosed asthma 
1.37 (1.23-1.53)
Asthma development 
 1.34 (0.86-2.10)
Adapted from Mudarri and Fisk as quoting Fisk WJ, Lei-Gomez Q, Mendell MJ, (2007) Meta-analyses of the associations of respiratory health effects with dampness and mold in homes.  Indoor Air 17(4): 284-295.  

Persons living in moist climates, flood prone areas,  poorly ventilated housing and poorly built buildings with plumbing problems are more likely to have conditions that are ripe for the growth of mould. A US study suggests that is about half the US housing stock.   So put simply, the problem likely affects half the US population, and while there may be reasons to think slightly less prevalence collectively in Canada, it is still much higher proportion than something like radon. 

Prevention is based on good construction practices.  In this respect, it is not surprising that mould has become a significant concern of First Nations. The fundamental problem is not the mould but the lack of application of Canada Building Code standards and lack of building inspection in housing construction on many reserves. 

Early Intervention:  Following a known water event; flooding, plumbing incidents, sewage back up – rapid drying and cleaning is very important. 

Mitigation  is not easy.  Cleaning is integral to reducing overall burden and often not adequately emphasized. Nor is a single cleaning likely to be sufficient for long term elimination of moulds.   Replacing water damaged materials is beneficial, recalling however that mould spores will have been widely dispersed within air spaces following water damage.  The Cochrane collaborative posted a recent review on the value of certain mitigation activities Cochrane review on mould mitigation.  

Perhaps just as disappointing is given the huge controversies regarding mould, and the burden of illness that  mould invokes, is the lack of public health attention to the basic problem of housing and mitigation of mould.  A good economic analysis from the EPA is available at Reprint of EPA funded work from Indoor Air Journal  and estimates the annual US costs at $3.5Billion for asthma alone. 

So while mould has received a bad rap through the toxic mould controversy, please don't underestimate its role as a very important public health concern and chronic manifestations of malaise.  

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