Environmental Reporter
Home > Resources > Education > Environmental Reporter > How Much Proof Is Needed To Determine That Mold Is Causing A Problem? | Curvularia species

How Much Proof Is Needed To Determine That Mold Is Causing A Problem? | Curvularia species

How Much Proof Is Needed To Determine That Mold Is Causing A Problem?

By Dr. Harriet Burge

How much proof is needed to determine that mold is causing a problem? The answer depends on innumerable factors, not the least of which is the definition of the word "proof". Proof, to a scientist, means that sufficient evidence has been gathered to demonstrate, using statistics, that there is less than a given probability (usually 5%, but sometimes 1% or even a 0.1%) that the problem is caused by a mold. Thus, any statement of "scientific proof" has a defined probability that it could be wrong. Generally scientists are only willing to be wrong 5%, or less, of the time. On the other hand, a jury may consider proof to mean a "preponderance of the evidence", which means that there is at least a 50% chance that the proof is wrong and the problem is not caused by mold. To a physician, any chance that a mold-related problem exists is worth consideration because of their obligation to the patient to be cautious. For this reason, physicians often propose low probability diagnoses and then seek to exclude them. In the case of a potentially life-threatening problem, a physician may even act on an improbable diagnosis if the action is relatively benign.

Obviously, it is much harder to meet the scientific definition of proof than it is to meet the "preponderance of evidence" standard, so what we consider "proven" may be different than what will win in court.

Scientists are convinced that there is a connection between mold and infections and allergies for certain populations of people. However, it can be difficult to establish that mold is actually the causative agent of these symptoms for the specific individual(s) being helped by an environmental investigator. Although environmental investigators must think somewhat like physicians, none are trained to diagnose connections between mold problems and human disease. The environmental investigator needs to remain focused on the environment. The fact that the scientific community agrees that mold can cause health problems is a solid basis for finding and eliminating indoor sources of mold from which aerosolization and human exposure is likely to occur.

In the case of the connection between "toxic" mold and human respiratory illness, scientists are not convinced that sufficient proof (to the 95% level) exists to make this connection. Juries, on the other hand, have been convinced to the 50% level (i.e., more likely than not) that individuals' health have been affected by inhalation of toxic mold spores. Many physicians are not convinced of the connection, but accept it, then seek to exclude the diagnosis.

How should an environmental investigator proceed, given these circumstances?
First and foremost, no environmental investigator can be expected to collect sufficient data to conclude, with 95% probability, that mold growth is causing a problem. (Note that they can conclude with 100% probability that mold growth is occurring if they see it!). Scientists have the luxury of not having to consider individuals and their day-to-day problems and, therefore, do not have to strike a balance between ideal and practical solutions.

Additionally, no competent investigator is going to be satisfied with being wrong 50% of the time. Juries do the best they can (often with no specific knowledge of the problem at hand) and are generally not affected, in the long run, by their decisions. Attorneys are paid and advance their careers by winning cases, whether or not they are defending the "truth". An environmental investigator, on the other hand, is expected to have specific knowledge of the problem and their business will certainly suffer if they are wrong.

I believe that environmental investigators are like physicians. They are trying to diagnose problems in buildings and they should examine all reasonable hypotheses. Of course, this approach requires education and training. An amateur cannot go into a building and make intelligent guesses. Making recommendations for remediation that take into consideration future problems that might occur if the recommendations are not followed, or the impact of the recommendations on the home or building owner or occupants, requires considerable knowledge and experience.

Because formal training programs are not available for mold investigators, acquiring the needed education can be difficult. I consider knowledge in the following areas essential for a good mold investigator:

1. Building science: How buildings are put together, how they operate, and how water travels through them.

2. Mycology: What fungi are, where they grow, how they spread, what are background levels and, very generally, what kinds of health effects might they cause (this last is only for perspective).

3. Sampling: What constitutes a reasonable sample of an environment (i.e., how much sample is needed); what kind of sample (and sample analysis) is most useful; how are samples handled; what kinds of information can be derived from samples; how is data interpreted.

4. Remediation: What kinds of remediation work best for preventing mold growth; how is mold effectively stopped and removed; how will remediations affect the environment; what are the implications if remediation recommendations are not followed.

Education in all of these areas can be obtained through extensive reading, attendance at short courses (or University-based curricula) and by working with experienced people (i.e., apprenticeships). Although basic knowledge in all of these areas is essential, nothing substitutes for experience and common sense.


Fungus of the Month: Curvularia species

By Dr. Srivandana Kilambi

Ever wonder during spring and summer why your lawn grass looks dried up with thinning irregular patches, and the leaves on your trees are turning yellow and brown from the tip down despite of all our care to revive it? Well, it may not be due to lack of constant care but due to a leaf spot fungus called Curvularia. It is a widespread airborne facultative weak pathogen of soil and plants, which mostly survives as a saprophyte in tropical and sub-tropical areas. Few are found in temperate zones, although spores are seen in the Midwest during fall crop harvest. Curvularia is easily isolated from dead turf (thatch) and other weakened dead plant tissue. Although it is primarily an outdoor fungus, Curvularia is often isolated from indoor building materials.

Curvularia was first described by Boedijn in 1933. Its teleomorphs are included in the ascomycete genus Cochliobolus. The genus Curvularia contains approximately 30 species. Cuvularia spp., are darkly pigmented fungi with spores (conidia) efficiently adapted for aerial dissemination. It has very distinctive and beautiful spores, which can be easily identified in both spore traps and direct exams. The shape of the spore is so distinct that it's name came from its shape. Microscopically, the spore appears boomerang shaped to more or less spindle shaped and bent. The spores are smooth walled with 3-4 true transverse septa (cross walls), resulting in 4 and 5 celled spores. In the 4 septate (5- celled) spores, the central cell is swollen, distinctively enlarged and darker than the other cells. In the 3 septate (4-celled) spores, the central crosswall is truly meridional (centrally located) and darker than the other two. Macroscopically, colonies on agar media appear black, hairy and expanding.

Agriculturally, Curvularia is known to be a plant pathogen, especially infecting grasses (e.g., sorghum, wheat, and corn). As mentioned above, it can also affect lawn grass in warm climates.

In the last half century, this species has emerged as a human pathogen, although such diseases are extremely rare outside of the tropics. Due to its relatively large size, the spore remains in the nose or sinus after inhalation. Rarely, a chronic, allergic sinusitis may be provoked in patients with existing allergic rhinitis (hay fever). A Serine protease has been identified as a major allergen of C. lunata. A potent mycotoxin curvularin has been isolated from C. lunata, a rice contaminating species. Experimental mycotoxicosis were produced in albino rats. Another toxin, curvularol, from Curvularia sp., RK 97-F166 (Nagasaki, Japan) inhibited cell cycle progression of normal rat kidney cells in G1 phase at 150ng/ml. These effects have not been observed in people, and exposure to sufficient toxin to cause illness is extremely unlikely.


1. Ellis, M. B., 1971. Dematiaceous Hyphomycetes. Common Wealth Mycological Institute, Kew, Surrey.
2. www.ttuhsc.edu
3. www.mycology.adelaide.edu.au
4. JCM (Journal of Clinical Microbiology) website.


This article was originally published on April 2005.