The floods have come and gone in Queensland and in their wake are heartbreak, devastation and months, if not years, of clean-up and rebuilding. Those affected now face a hidden risk to their health from water-damaged, damp and mouldy buildings.
There is a large body of scientific evidence that supports an association between various health problems and damp, mouldy environments. This evidence was examined and summarised in a 2004 Institute of Medicine report and a 2009 World Health Organisation report. The message is clear: damp home environments are associated with respiratory problems including asthma, coughs, respiratory infections and upper airway problems.
But the cause-and-effect proof for this association is lacking. In other words, while damp living environments is associated with increased risk of a number of respiratory symptoms, the reason the risk increases is unknown. It’s tempting to conclude that mould is the cause, as mould grows in damp conditions and, in many cases, visible mould is reported in damp housing.
Mould exposure and health risks
Moulds are complex organisms that are difficult to quantify reliably. Mould is associated with two broad categories of human illness: infectious diseases and non-infectious illness, usually allergy-related conditions.
Invasive (infection-causing) illness caused by mould is uncommon and usually occurs in people whose immune systems are compromised. There was no measurable increase in invasive mould infection reported in New Orleans after Hurricane Katrina, perhaps the best studied model for post-flood health effects.
Allergic sensitivity to various moulds, detected by skin and blood tests, is associated with exacerbation of asthma. There’s evidence linking asthma exacerbation in sensitised individuals to damp indoor environments, but not enough evidence to suggest that such environments cause asthma.
There are non-immune effects of mould exposure and these are mostly irritant in nature. Exposure to high levels of (1-3)B-D-glucan, a chemical found in mould cell walls, has been linked to chronic cough, throat irritation and irritation of upper respiratory tract.
Damage from damp
Along with mould, numerous bacteria and amoeba species may flourish in damp housing, and there may be synergistic effects between them and other toxins, an area open to further research.
Damp buildings often have raised levels of endotoxins (toxins within bacteria). Endotoxin has been associated with animal exposure and farm environments, and may protect against the development of allergic conditions. But in association with other dampness-related factors, it may have negative effects.
There are also other potentially harmful factors to consider. Flooding and dampness may damage building materials and furnishings, causing them to release toxic chemicals such as formaldehyde from composite wood products and plasticizers (2-ethyl-1-hexanol) from vinyl flooring.
As you can see, there are many factors to consider when attempting to establish causal relationships between dampness and respiratory illness. This explains why proof of cause and effect has been difficult to obtain.
Lessons from Hurricane Katrina
The devastation of New Orleans caused by Hurricanes Katrina and Rita left communities homeless and entire suburbs destroyed. The clean-up was massive, taking many people months and years and exposing them to damp, mouldy environments. Many of those involved in restoration developed a chronic cough, which was dubbed the “Katrina cough” and became widespread after the hurricanes. It was attributed to irritant phenomena.
A number of scientific studies monitored and measured the health effects of long-term exposure to damp, mouldy environments. Monitoring demonstrated high mould and spore levels in the wake of Katrina, but the clinical studies performed at the time did not show the anticipated impact on health.
A 2006 study looking at 50,000 visits to emergency departments and medical clinics measured presentations for cough, wheeze, sinus drip, sore throat and chest congestion and found no increase in respiratory presentations compared to other parts of the country. But those with a history of asthma were more likely to experience symptoms because of mould and dust exposure.
Problems with sampling, bias in reporting and use of qualitative assessment have been cited as possible reasons for a lack of association in these studies.
Chronic allergic and non-allergic respiratory diseases are global problems that extract enormous human, economic and social costs. It’s estimated that 20% to 50% of all building stock in the United States and Europe have problems with damp. If the two are linked, then removing pollutants from housing and better planning and building codes must become a priority. The challenge to the scientific community is to clarify the components of dampness that are key, how to measure them and how to effect change.
As Queensland cleans up from the floods, it’s important that asthmatics wear good-quality face masks while handling mouldy things. If someone is immunosuppressed (for example, receiving chemotherapy for cancer), it’s best for them to stay out of the environment or wear proper respiratory protection.
Where possible, infants and young children shouldn’t be continuously exposed to mouldy environments. Most important for those in flood-affected areas is cleaning up and restoring a dry living environment as quickly as possible.