home News Hurricane Sandy and the Microbiology of the Built Environment: Guest Post by James Scott.

Hurricane Sandy and the Microbiology of the Built Environment: Guest Post by James Scott.

(The following is a guest post by James Scott, from the University of Toronto)

The receding waters of hurricane Sandy left a trail of destruction along the eastern seaboard of North America – demolishing homes and businesses, flooding neighborhoods and transportation systems, disrupting electricity and water supplies. The havoc wrought by Sandy poignantly affirms the brutal power of nature, eerily echoing the fury that hurricane Katrina inflicted on the Gulf Coast seven years ago, and the much more recent devastation brought by the Haitian earthquake in 2010 that left a country in ruin and over a million people homeless. While the damage left by Sandy awaits finally tally, early estimates place reparation costs over $52 billion, just half that of hurricane Katrina, making Sandy the second costliest US Atlantic hurricane – nearly double hurricanes Ike in 2008 and Andrew in 1992.

Damage to Casino Pier in Seaside Heights, New Jersey (from Wikipedia)

The shocking images, captured furtively in the worst minutes and systematically throughout the aftermath, document the singular, raw and unmitigated power of these events. Still, these physical effects are only a portion of nature’s full destructive force. In the days and months following a catastrophic storm or flood, a methodical but correspondingly fierce second act unfolds, performed this time not by physical agency but rather biology in the form of microbes, most notably molds. Within as little as a day or two after flooding, molds sprout, awakened by a rush of moisture and nutrients. In a month’s time, if their growth remains unchecked, nothing is likely to remain beyond their grasp.

Indoor mold

Molds are some of the least noticed though arguably most influential members of the strange kingdom of creatures known as Fungi, whose ancient ancestry is to be sought somewhere midway between Animals and Plants. Unlike their large and showy cousins, the mushrooms, molds bear their spores on microscopic reproductive organs that pepper the surface of their characteristic ever-widening fuzz. Devouring the traces left behind by other organisms is the most passionate and proficient activity of mold, whether the target is scraps of wood or paper, biscuit crumbs, toenail clippings, or leftover meatloaf.

Given that there is never any lack of either mold spores or appealing residues, one wonders why all earthly matter has not surrendered to mold’s unseemly embrace. The key lies in water, or rather in the lack of it. Water is the third prerequisite in the unharmonious triad of decay. Its absence is protective, its presence destructive. Moisture is mold’s universal call to action. Hence, to control moisture is to control decay. Getting things dry is the first and most urgent step in mold prevention.

Molds and health

For the most part, molds and humans lead a peaceful, even mutually beneficial co-existence. The conflicts that arise between us and our diminutive neighbors, the molds, usually involve property disputes: rights to a refrigerated leftover, claim to a closet wall, or ownership of a vital organ (problematic when its human proprietor has not yet finished with it). In asserting their entitlement to our possessions, molds exert a variety of effects upon hapless humans, some intended, others accidental.

Since the latter part of the 20th century, we have become increasingly aware of their impact on our health and well-being. In particular, indoor pollutants such as molds have received considerable scrutiny as contributors to human illness. Scientists have convincingly linked the growth of mold in houses to numerous health problems. People should not live in moldy houses. To do so can jeopardize health. This concept is not a new one, but scientists are now beginning to understand the short-term and long-term health consequences of living in mold-contaminated housing. It does not matter what type of mold is involved, it simply needs to be cleaned up.

Repairing mold damage

Several years ago I wrote a guide on behalf of Canada’s national housing authority, CMHC, describing approaches to cleaning up mold in buildings (Scott 2004). Others since have produced highly useful documents on mold and other microbial problems on a larger scale associated with flooding and natural disasters (Brandt et al 2005; 2006). Particular attention is given to a rapid response in drying affected materials as a way to minimize or prevent mold growth. This ideal is challenging to meet, especially in the setting of an emergent disaster. Often clean-up efforts must be prioritized, with many buildings remaining damp well past the point when mold is likely to grow. These buildings will require later evaluation to determine how clean-up efforts should be deployed. However in all cases, environmental sampling for mold is not routinely done to assess a building (Brandt 2005). Instead, a thorough visual inspection to evaluate the extent of the mold problem is usually all that is needed to determine clean-up strategies and protective measures. Brandt et al (2005) expanded on this general concept and noted the few situations where sampling might yield useful guidance:

If visible mold is present, then it should be remediated regardless of 1) what types of microorganisms are present 2) what species of mold is present, and 3) whether samples are taken. Other than in a controlled, limited, research setting, sampling for biological agents in the environment cannot be meaningfully interpreted and would not significantly affect relevant decisions regarding remediation, reoccupancy, handling or disposal of waste and debris, worker protection or safety, or public health. If sampling is being considered, regardless of the purpose, there should be a clear question that the sample results will help to answer. The following are examples of instances when different types of sampling may be required:

– To help evaluate a source of mold contamination. For example, testing the types of mold and mold concentrations indoors versus outdoors can be used to identify an indoor source of mold contamination that may not be obvious on visual inspection.

– To help guide mold remediation. For example, if mold is being removed and there is a question about how far the colonization extends, then surface or bulk sampling in combination with moisture readings may be useful to answer this question.


Physical removal of heavily damaged materials coupled with normal cleaning for incidentally contaminated items is usually sufficient to remove mold (Scott 2004). Biocidal chemicals are useful supplements to cleaning when the contaminants in question are also an infectious substances (e.g., hospital pathogens), but they are not useful in mold clean-up. This is because no commonly occurring indoor fungi regularly cause human infection and most do not respond uniformly well to biocides. To the contrary, the most significant hazards presented by environmental molds exist whether the spores are living or dead. Despite a great many marketing claims to the contrary, there is no spray, gas or other quick treatment that short-cuts this process. Once again, the only way to prevent mould problems is to eliminate superfluous moisture and safely clean or discard affected items.


  1. Brandt M et al. 2005. Prevention strategies and possible health effects in the aftermath of hurricanes Katrina and Rita. CDC Mold Work Group. Atlanta GA: US-CDC.
  2. Brandt M et al. 2006. Mold prevention strategies and possible health effects in the aftermath of hurricanes and major floods. MMWR June 9, 2006 / 55(RR08);1-27
  3. Scott JA. 2004. Clean-up procedures for mold in houses. Ottawa, Canada: Canada Mortgage and Housing Corporation (CMHC).



David Coil

David Coil is a Project Scientist in the lab of Jonathan Eisen at UC Davis. David works at the intersection between research, education, and outreach in the areas of the microbiology of the built environment, microbial ecology, and bacterial genomics. Twitter

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