False Negative Mold Test Results & What They Mean InspectAPedia® -
What causes False Negative or ok toxic mold test results - and why are these a Source of Error in Indoor Mold Tests
What are the sources of variation in the mold level that air tests can detect?
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Here we define and explain the causes of False Negative or ok toxic mold test results as Sources of Error in Indoor Mold Tests. This document is a brief tutorial which provides information about the accuracy of and sources of errors in tests for the level of allergenic and toxic mold in residential buildings: Are
spore counts valid? Are cultures and swab tests valid? These critical questions are discussed in this paper.
Readers should also see MOLD LEVEL IN AIR, VALIDITY, and
for a more in-depth critique of popular mold testing methods than this
tutorial see MOLD TESTING METHOD VALIDITY
Mold spore counts are questionable in the first place, given the high variability that we discuss in this article.
But "low" or "negative" mold spore counts, especially if not accompanied by a thorough visual inspection and collection of the building's
leak history and occupant complaint history, are particularly suspect.
Individual samples of particles in air show tremendous variation from minute to minute, making "ok" airborne mold spore test results a thing to view with skepticism.
Examples of factors which can cause an exponential difference in particle levels in indoor residential air over short time intervals include: mechanical disturbance (walking across a carpet or
moving a moldy cardboard box), operation of hot air heating system or central air conditioning system, operation of other building fans, particularly ceiling
fans and vacuum cleaners, turning lights on and off, and opening or closing windows and doors. In situations of particular risk, additional or periodic testing should be considered.
Below we list these sources of mold test variation and give photos and mold test examples for specific variation sources.
Our experience is that the variation in the level of small (mold spore sized) indoor airborne particles is so significant that any indoor airborne particle count is likely to be an inaccurate
guess at the actual occupant exposure level where indoor problematic molds are present. This means that visual inspection, building history,
and occupant complaints or occupant health fragility need far more attention than they receive if the "mold investigator" simply
performs a cursory visual inspection or worse yet, simply collects a few air samples in a building.
At Conditions that Cause High Variation in Indoor Airborne Particle Levels
this article list some of the chief sources in the short term variation in the level of airborne particle levels.
Even if we used a long term sampling method, say 24 hours, or interval sampling over days, these same variations will occur, and worse,
without careful study of the actual sources of airborne particle level variation in a specific building, and without a documentation of
the typical conditions in the building during the time that it is occupied we cannot describe the occupant exposure level
with any accuracy whatsoever.
Risk of false negative mold tests: Experienced mold contamination investigators should have little confidence that a one-time low or "ok" "toxic mold test spore count" is an assurance that problematic particles are not
present.
The presence of certain spores or fungal particles, even at low levels in air can indicate or confirm an indoor reservoir and amplifier of mold spores
in the building, particularly if a careful microscopic examination of the "low level" sample contents shows evidence of nearby
active fungal growth such as Aspergillus sp. or Penicillium sp (or certain other genera/species) spore chains.
The presence of extensive off-season pollen can also indicate a pollen reservoir in the building - a potential concern for people with
pollen allergies or asthma.
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Additional technical contributors & reference sources for this article are listed below.
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Thanks to Susan Flappan, Flappan Consulting, moldetect.com, Overland Park KS, 913-402-1131, for contributing comments and some suggested text from ACGIH Bioaerosols: Assessment and Remediation 12/2006.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home",
U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon)
Atlas of Indoor Mold, Online Clinical Mold Atlas, Toxins, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
Black Mold that is Harmless Photos of recognizable, usually harmless black mold on wood, bluestain, ceratocystis, ophistoma
Building Floods: quick steps after a building flood or plumbing leak can prevent costly mold contamination
Classes of Mold: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
"Disease Prevention Program for Certain Vegetable Crops," David B. Langston, Jr., Extension Plant Pathologist - Vegetables, University of Georgia (PDF document) original source: www.reeis.usda.gov/web/crisprojectpages/209797.html
"Disease Prevention in Home Vegetable Gardens,"
Patricia Donald,
Department of Plant Microbiology and Pathology,
Lewis Jett
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold
Mold or allergens may not be the only or even the main indoor environmental contaminant. Don't let media attention to mold
cause so much enviro-scare fear that other, possibly more urgent hazards go un-addressed.
Ozone Warnings - Use of Ozone as a "mold"
remedy is ineffective and may be dangerous.
Pet control - if you can't say goodbye to your bird, cat, dog, guinea pig, hamster, tropical fish, then limit the
areas they occupy and limit the airflow from that area to sleeping or other areas of the building, use allergenic
bedding, eliminate wall-to-wall carpeting, improve housecleaning including use of a HEPA-rated vacuum cleaner. For more details
see our article Dog, Cat, and Other Animal Dander - Information for Asthmatics and Indoor Air Quality
Rodents, Mice, Squirrel Control - I find high levels of mouse and rodent dander, fecal dust, and urine-contaminated dust in some buildings,
and high levels of these materials in building insulation in those locations. If you have a mouse problem, particularly if mice and their waste (fecals or urine) are contaminating
the building HVAC or building insulation, may need both steps to clean up or remove infected materials and steps to stop an ongoing
rodent problem. If squirrels are a problem, the cleanup needs to include closing off entry openings into the building. Get some
help from a licensed pest control expert.
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