The Consequences of Flooding: Mold, Mycotoxins, and Bacteria; Oh My!!

Flooding and water damage can happen when you least expect it. Severe weather patterns such as hurricanes and heavy rain can have an impact on the buildings integrity, causing moisture retention and microbial growth.

Hello again to the TMP blog. This month we are going to talk about flooding, mold, mycotoxins, bacteria, and Endotoxins.  The southern and eastern parts of the United States have experienced extreme weather the last several months.  Similar to previous years, hurricanes and tropical storms have led to large amounts of rain and flooding.  In this article I will discuss how previous storms have led to massive amounts of mold growth and environmental illnesses.  

In 2005, the hurricanes Katrina and Rita caused massive rainfall and flooding in the southern parts of the United States.  In New Orleans the levees protecting the city broke, which resulted in the flooding of thousands of houses. About 134,000homes flooded in the New Orleans area(1). Some homes remained underwater for weeks and when it receded many were concerned with mold and bacterial growth. The studies done afterwards can give us some insight into what we might experience in the next few months as well as into next year.  

As seen in table 1 (from Solomon et al) the number of different types of molds increased dramatically in the flooded verses the minimally flooded homes.  In the flooded homes there are measurable amounts of Stachybotrys (the infamous black mold), however, both flooded and minimally flooded we see Aspergillus and Penicillium. Studies of spore concentrations showed that the amount of mold spores increased in the homes that were flooded increased between5-10-fold (2) as seen from table 2 (also from Solomon et al).  Seeing Aspergillus/Penicillium in both is not surprising because of their ability to thrive in drier environments.  The high humidity in the New Orleans area makes these types of molds very prevalent in without dangerous storms.  This same study found no increase of endotoxins in homes that were affected by flooding (2).

Table 1: Fungal taxa identified at >1% of total spore count.
Table 2: Daily mean fungal spore concentrations and predominant taxa: indoor sampling sites.

These increases in molds also led to increased in respiratory issues in children around New Orleans.  Months after the storms, doctors saw 100% increase in upper and lower respiratory issues(2). These respiratory problems are most likely caused by allergenic reactions to mold (i.e. IgG and IgE reactions). Later problems such as headaches, nerve inflammation, memory issues, and immune reactions were later seen in these populations (3). These issues can most likely be attributed to the formation of mycotoxins from molds that thrived in these wet and humid conditions.  The presence of mycotoxins in homes affected by flooding from the hurricane was confirmed by a study (4). I have talked with a lot of individuals that were dealing with these mold issues 5-10 years after this hurricane. These are issues that won’t go away on their own and should be dealt with.  So, what should a home owner do?

I’m sure most people are aware of the Ben Franklin quote “an ounce of prevention is worth a pound of cure.”  That is very true in these cases.  Here are some important aspects to consider:  

· Any structure flooded after hurricanes or major floods should be presumed to contain materials contaminated with mold if those materials were not thoroughly dried within 48 hours.

· Cleanup and dry out the building quickly. Open doors and windows and use fans or dehumidifiers to dry out the building.

· Remove all porous items that have been wet for >48 hours and that cannot be thoroughly cleaned and dried. These items can remain a source of mold growth and should be removed from the home or building. Porous, noncleanable items include carpeting and carpet padding, upholstery, wallpaper, drywall, ceiling tiles, insulation material, some clothing, leather, paper, some wood and wood products, and food. Removal and cleaning are important because even dead mold can cause allergic reactions.

· Clean wet items and surfaces with detergent and water to prevent mold growth.

· Temporarily store damaged or discarded items outside the home or building until insurance claims can be processed.

· All surfaces of an HVAC system and all its components that were submerged during a flood are potential reservoirs for dirt, debris, and microorganisms, including bacteria and mold. In addition, moisture can collect in areas of HVAC system components that were not submerged (e.g., air supply ducts above the waterline), and this also can lead to the growth of microorganisms. Therefore, all flood water-contaminated and moisture-laden components of the HVAC system should be thoroughly inspected, cleaned of dirt and debris, and disinfected by a qualified professional. If HVAC systems are not properly cleaned and disinfected to prevent the dissemination of mold and other debris throughout abuilding, bioaerosols of mold and other microorganisms might exists and can cause a variety of adverse health effects to the building's occupants. Ensure that the HVAC system is shut down before any remedial activities.


If you have a home that was affected by severe weather, please let us come in to see if mold growth has been root in your home.  Early detection can help prevent further spread and will help prevent medical issues down the road.  As I said in an earlier blog “Mold is rarely a do-it-yourself project.”  I hope this info helps and hopefully we can help you in the future.

Resource List

1. L. Manuel, One year later: remembering Katrina caregivers. RN 69, 14 (2006).

2. G.M. Solomon, M. Hjelmroos-Koski, M. Rotkin-Ellman, S. K. Hammond, Airborne mold and endotoxin concentrations in New Orleans, Louisiana, after flooding, October through November 2005. Environ Health Perspect 114, 1381-1386 (2006).

3. M. Brandt et al., Mold prevention strategies and possible health effects in the aftermath of hurricanes and major floods. MMWR Recomm Rep 55, 1-27 (2006).

4. E. Bloom, L. F. Grimsley, C. Pehrson, J. Lewis, L. Larsson, Molds and mycotoxins in dust from water-damaged homes in New Orleans after hurricane Katrina. Indoor Air 19, 153-158(2009).

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