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HomeSampling Mold Growth

Is Sampling and Testing for Indoor Mold Growth Necessary?

Questions always arise as to whether sampling for mold in the so-called sick building environments is necessary, especially if mold growth is visible. This question may be difficult to answer if the objectives of the overall investigations are not well defined. The first step would be to define the problem to be investigated and then formulate the objectives of the investigation. The objectives for sampling for mold may be as basic as:

• To confirm whether certain discolaration or staining on a surface is mold growth or not, and if mold which one? For visible mold growth, precise identification of the type of mold is important to:
  
  • Ensure that the correct mold removal strategies are used.
  • Avoid confusion with similar molds that may not present a problem. Also, building occupants may need assurance that they were not exposed to molds that may cause health problems.
  • Document the identity of the molds involved in case of litigation.
  
  
• To determine the presence/absence of airborne spores, and their composition and concentrations in situations where occupants complain of ill health but with no obvious visible mold growth. This information could be used in assessing the possibility of hidden mold growth and human exposure.
• To determine if spores from visible mold growth sources have become airborne. The information obtained in this case can be used as background information in monitoring the effectiveness of mold removal measures and/or as an indication of human exposure.
• Specific objectives may be to detect and quantify certain mold species, for example, in hospital environments, the objectives may include the following:
  
  
  • Detecting the growth of Aspergillus fumigatus, Aspergillus flavus and Aspergillus niger which are causes of Aspergilloses in immuno-compromised patients.
  • To determine if outbreaks of invasive aspergillosis were due to hospital construction or demolition activities
  • To determine potential sources of nosocomial aspergillosis
  • To monitor environmental spore contamination from outside sources
  • To identify cleaning procedures that may release high concentrations of airborne Aspergillus spores
  • To evaluate the efficacy of HEPA filters in laminar flow facilities
  • To evaluate efficacy of procedures to contain hospital building work from hospital wards and other areas where high risk patients are managed
  • To determine the level of mold contamination before initial occupancy of special controlled environments such as the operating rooms

Once the objectives of the investigations have been defined and the decision has been made to sample, the next question to answer is what data are required, e.g., is identification to genus sufficient?, is quantification required? The type of analytical data required will determine the type of samples to take and how many. The level of analytical details required depends on the questions the analytical results are required to answer. For example, if the investigator wanted to know whether certain discolorations were mold or due to mold growth and if so, which mold?, then a lift tape sample for direct microscopic examination (DME) analysis would be sufficient.

Types of Samples

Air Samples

It may not be necessary to take air samples if mold growth is visible. However, if mold growth is not visible, air samples could help in detecting hidden mold. Air samples can be collected in two ways:

• by impacting air on sticky surfaces for non-viable (non-culturable) analysis or
• by impacting air on some suitable growth media for viable (culturable) analysis.

If the objective of air sampling was to estimate the total airborne mold spore concentration, then sampling for non-culturable air testing would be selected. Non-culturable air testing for allows for determination of total fungal spores and hyphal fragments concentration since the particles are directly enumerated under a microscope. The other advantage of non-culturable analysis is that results can be obtained within a few hours after air sampling which is good for pre- and post-remendiation. However, non-culturable analysis does not allow for identification of mold spores to species and some spores (at times majority of spores) are reported as unidentified spores. On the other hand, if the objective of air sampling was to identify airborne species of molds or bacteria in the environment, then sampling air for culturable analysis would be the obvious choice. However, air sampling for culturable mold testing has two major disadvantages:

• Only the culturable structures (spores, hyphal fragments) can be detected on the growth media as colony forming units (CFUs). Also not all culturable structures would be detected because individual growth medium tend to be selective against some molds. Again, some molds tend to overgrow or inhibit the growth of other microorganisms. This means culture test could significantly under-estimate the contamination level of the air sample.
• Results take 10-15 days or more to be available.

The major advantage of culturable analyses is that resulting colonies of bacteria or mold can be identified to species. Some mold species such as those of Aspergillus, Fusarium and Penicillium are opportunistic pathogens. Therefore, their correct idenitification in hospitals and homecare facilities is critical.

Bulk and Lift Tape Samples

Bulk samples with or without visible mold growth are suitable for analysis. Bulk samples include pieces of building materials such as drywall, insulation material, baseboards, ceiling and floor tiles, carpets, or even dust. Collection of bulk samples may involve destructive sampling and should only be collected if other means of sampling, such as lift tape, are not possible or more detailed analyses than would be obtained from lift tape are required. Bulk samples can be analysed in two ways:

• Direct microscopic examination (DME) - DME is a non-culturable analysis, therefore results can be obtained on the same day. It is suitable for confirming mold growth or simply for identification of mold from surfaces with visible mold growth.
• Culturing - In culturing, pieces of bulk sample or lift tape are placed on suitable growth media and incubated. The major disadvantage of culturing is that only culturable microorganisms will grow on media. Therefore, unless it is critical to know the species of the culturable microorganisms on the bulk sample (which a good mycologist may determine using DME), it is not necessary to ask the lab to culture bulk samples.

Tips:

1. If bulk samples with visible mold growth are to be cultured, it is recommended to have the material also analysed by DME. DME allows the dominant molds on the sample to be identified, whereas with culturing alone, the dominant mold may not be culturable or may be masked by fast growing or inhibitory molds.
2. Microbial contamination on bulk samples could be quantified as Colony Forming Units (CFU) through serial dilution. Serial dilution allows a diversity of microorganisms to be recovered on culture media. The CFU data from bulk samples, however, is questionable due to a number of technical reasons.
3. It may be better to analyse dust samples by culturing than by DME but the limitations of culturing need to be considered.

Surface Samples

Surface samples are either:

• Lift tape samples
• Swab or wipe Samples
• Agar contact plates

These samples could be used to determine the level of contamination on a surface. They may also be used to demonstrate that a surface is "clean" after remediation work (but one has to be aware of the limitations of this kind of sampling). Lift tape is usually analysed by direct microscopic examination (DME). It can also be cultured. One major disadvantage with tape is that it is not suitable on wet and uneven surfaces. Swabs and wipes can be analyzed by DME or culturing. Tape sampling is not suitable for bacteria analysis.

Dust Samples

There could be many reasons why an investigator would want to take dust samples. Dust samples give an indication of the types of microbial particles that have settled on the surface over time. Therefore, dust samples could give an indication of whether there is hidden mold. However, dust from carpets may also contain microbial particles brought in from outside through soiled shoes or other items brought into the building from outdoors.

Collecting and Sending Samples To A Lab

The quality of laboratory results will depend on how the samples were handled during collection and shipping and also how they were handled by the receiving lab. There are specific procedures for collection, handling and shipping of samples of each type discussed above. For a copy of these procedures, please contact us or click Sending Samples. MBL is also happy to assist you in defining the objectives of sampling and determing the most suitable types of samples to collect, how to collect them and the analytical method(s) to use. Please call us or just fill in your questions in this form and send them to us.