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How To Interpret Laboratory Results for Airborne Fungal (Mould) Samples

Laboratory results for airborne mould and bacteria concentrations can be difficult to interpret for two major reasons.

  • Maximum exposure limits have not been set
    Currently, there are no set maximum exposure limits (MELs) or threshold level values for airborne indoor mould and bacteria concentrations. Setting MELs would be difficult for reasons which include limitations in air sampling techniques (Kung’u, 2004), variability in sensitivity to microbial exposure among the human population, occurrence of a large number of different types of biological and chemical pollutants in indoor environment (Morey, 2001) and limited data on exposure-response relationship.
  • Failing to clearly define air sampling objectives
    In some cases investigators fail to clearly define the objectives for taking air samples for microbial analysis. A well defined sampling objective helps the investigator to design an appropriate sampling strategy which includes the data required and hence the type of samples to take (i.e., viable or non-viable), the minimum number of samples to take, when to take them and how to interpret the resulting data. An initial walkthrough of the building under investigation is recommended prior to designing the sampling strategy.

Principle guidelines in data interpretation

In absence of set MELs, concentrations and composition of indoor airborne mould and bacteria are compared with those of outdoor (Miller, 2001, Health Canada, 2004). The investigator, therefore, should have some background information on:

  • typical airborne fungal or bacteria concentrations including seasonal, diurnal and temporal variation in concentrations and composition for outdoor and indoor environments,
  • factors affecting airborne microbial concentrations,
  • mycological or bacteriological terms used in the reports.

Understanding Terms Used in Laboratory Reports

Terms used in non-viable analysis report

Mould spores sampled from air

Amerospores: single celled spores (width to length ratio <15:1). Since spores from many groups of fungi can be referred to as amerospores, this term is not useful in reports.
Basidiospores: spores produced by a group of fungi called basidiomycetes, for example mushrooms, some wood-rotting fungi.
Ascospores: spores produced by a group of fungi called ascomycetes
Smut: refer to spores produced by smut fungi.
Rust: refer to spores produced by rust fungi.
Myxomycetes: slime moulds. Not true moulds.
Hyphal fragments: refer to fragments of the filamentous structures (hyphae) that make up the body of moulds by branching extensively to form a complex network called mycelium.

Terms used in Viable Analysis Report
Colony Forming Units (CFU): for moulds, a colony refers to a group hyphae. The term “Units” refers to the mould component(s) from which a colony developed. The unit could be a single spore or a single hypha, a group of spores or hyphae or a mixture of both spores and hyphae.
Non-sporulating (non-sporing) isolates: refer to moulds that fail to produce spores either because they have lost this ability, conditions were not suitable or requires very long periods to produce spores. Fungi that are strictly non-sporulating are called mycelia sterilia (sterile mycelia).
Sp (plural written as spp).: short form for species, e.g., Penicillium sp or Penicillium spp referring to a single species or more than one different species of Penicillium respectively.

How to interpret laboratory reports

Air samples on RCS agar strips
Air samples on RCS agar strips

As indicated above interpretation of airborne concentration of indoor moulds and bacteria is primarily based on experience and professional judgement. Basic knowledge in ecology of moulds is helpful. For example if lab results show that dominating spores for an indoor sample were mainly smut and rust spores while the outdoor sample showed dominant moulds as Aspergillus/Penicillium, then the investigator would suspect the samples were swapped and may want to resample again. To be able to interpret the results there are key steps to follow:

  1. Review the air sampling objective Let us say the primary objective of the investigation was to determine if there were elevated mould spore concentrations and/or indoor amplification sources in complainant room.
  2. Bearing in mind the sampling objective, compare total airborne spore concentrations from complainant room with those from outdoors and non-complaint rooms. This would answer the question whether levels of mould spore concentration were elevated in complainant room compared to outdoor and non-complaint room.
  3. Compare the dominant spore types (and their concentrations) from complainant room with those from control samples. Our objective was also to know whether there were amplification sources in the complainant room. The data we need to answer this question are:
    • Dominant moulds present in complainant room but not in the control samples. For examples if Cladosporium is dominating in complainant room but is insignificant in outdoor and control sample, we can conclude the source is in complainant room, even though Cladosporium can originate from outdoor.
    • Presence of indicator moulds. These are moulds frequently found in water damaged buildings. These include Aspergillus and Penicillium species, Acremonium spp., Sporobolomyces spp., Stachybotrys chartarum, Memnoniella echinata, Tritirachium oryzae, Ulocladium botrytis, U. chartarum, Cladosporium spp., and Chaetomium spp.
Air Sample taken with an Andersen Sampler
Air Sample taken with an Andersen Sampler

Some of these moulds such as Aspergillus fumigatus, A. niger, Penicillium oxalicum, P. thomii, and Cladosporium species, may also originate from outdoor environment. Building history i.e., whether there has been previous water problem would give further evidence as to whether there was mould growth in the complainant room. Register for the course How To Interpret Mold Results to earn more.

For details about mold and bacteria testing, contact us via phone or email.

References

Kung’u, J. N.(2004). Limitations and Considerations in Air Sampling, Sample Analysis and Result Interpretation for Airborne Mould Spores. Inoculum, 55(5):1-4.

Miller, J.D. (2001). Mycological Investigations of Indoor Environments. In: Microorganisms in Home and Indoor Work Environments. Diversity, Health Impact, Investigation and Control. Edited by Brian Flannigan, Robert A. Samson and J. David Miller. Taylor & Francis, London and New York 2001, hard back ISBN 0-415-26800-1. Pages 231-246.

Morey, P. R. (2001). Microbiological Investigations of Indoor Environments: Interpreting Sampling Data- Selected Case Studies. In: Microorganisms in Home and Indoor Work Environments. Diversity, Health Impact, Investigation and Control. Edited by Brian Flannigan, Robert A. Samson and J. David Miller. Taylor & Francis, London and New York 2001, hard back ISBN 0-415-26800-1. Pages 275-284.

How IAQ Professionals Can Improve Their Laboratory Reports

Currently there are no standardized methods for the analysis of indoor samples for microbial contamination. Neither are there guidelines for the limit of what is to be reported by laboratories and how to present the results.

Without guidelines reports from different laboratories are difficult to compare. The quality of laboratory reports is also sometimes compromised. Despite lack of standards and guidelines, the quality of laboratory reports could be improved with better communication between the IAQ professionals and the microbiologists.

While the microbiologists may be conversant with the biology, ecology and physiology of the organisms they deal with, it is possible that they may have very little knowledge or idea of what data would be most relevant to investigations on indoor microbial contamination.

Quality Microscope for Quality Service
Quality Microscope for Quality IAQ Service

Unlike with clinical samples where presence of certain organisms is enough to make decisions on the treatment to administer, with IAQ samples the types of organisms present, their quantities and the visual inspection data of the contaminated place are used to decide whether remediation is necessary and the level of containment required.

The microbiologist understands the laboratory data well and the methods they have applied while the IAQ professional has the field data such as the size of the area colonized, history of the building, occupants health information and other useful data which should be used together in decision making. A two-way communication between the microbiologist and the IAQ professional is therefore critical.

This article is an attempt to provide the kind of information the IAQ professionals and microbiologists should exchange to improve the quality and usefulness of laboratory results.

How the IAQ professionals could help improve laboratory reports

  • Discuss with the laboratory the objectives of the investigation: If the laboratory understands the objectives of the investigation, they may help in deciding the most suitable types of samples to collect for the intended investigation. The laboratory would also know what to report and how to report it. (click this link for information on how to collect and send samples).
  • Provide adequate amount, size and/or number of samples for analysis: The size or amount of sample should be adequate to allow the microbiologist to perform the test and retain some of the material for reference or for retesting in case something goes wrong during the first test or if detailed tests were required after the initial basic test. Where resources allow, the minimum number of samples that can allow statistical analysis of the resulting data should be provided.
    • IAQ Sample Analysis Flow Chart
    Sample Analysis Flow Chart
  • Provide clear instructions on the tests required: If the IAQ consultant has not discussed the objectives of the investigations with the laboratory, they should clearly indicate the tests they require the laboratory to perform and how they desire the results reported or presented. This is particularly important with some types of samples that can be analysed in more than one way (see sample analysis flow chart below).

    For example a swab or a dust sample can be analysed by direct microscopic examination (DME), culturing by direct plating or culturing for quantification (serial dilution). The results for quantification could also be expressed as colony forming units (CFU) per unit area (or per unit weight in case of dust). Each of these analytical methods has its own limitations and gives different data.

    Similarly a bulk sample such as a drywall could also be analysed by culturing or DME. If the laboratory is not directed on what analysis to perform, they may use methods which may not give the results that were expected by the consultant or that may not adequately answer the question being investigated. For instance if the consultant was interested in species present on a bulk sample, DME analysis may not provide this information. The flow chart below shows how various samples could be analysed.

How laboratories could improve the quality of their reports.

  • Give adequate information in the reports: Inadequate information may lead to inappropriate decisions being taken. So, reports generated by the laboratory should include adequate, useful, organized, informative and easy-to-understand information.
  • Provide helpful comments in the reports: Reporting without comments may also lead to inappropriate action. Consider this case: a consultant takes pre-remediation (background) air samples to a laboratory. The samples are highly overloaded with dust particulates and therefore become difficult to analyze. The resulting counts are therefore very low. After remediation, samples are taken again to assess the effectiveness of remediation. This time the samples are not overloaded with dust and counts are significantly higher than the pre-mediation results. If the lab had commented on the first report that the samples were overloaded with dust and that this may result to low counts, the consultant would have decided on whether to take another set of samples or not.
  • Provide information on medical significance of reported moulds: Most laboratories avoid commenting on the medical significance of the moulds or bacteria they identify claiming that they were not qualified to make such comments. While this is true, one of the most important functions that a laboratory should perform is to decide what organisms are of health concern and what constitutes normal flora since this information is already documented in reputable journals or textbooks. By providing this information the laboratory is not in anyway taking the role of medical professionals. If such information is not available the laboratory should indicate so in the reports.
  • Provide a list of references: The laboratories should provide a list of references where the consultant can obtain more information concerning the identified moulds and bacteria and their health significance.

Conclusion

Communication between the IAQ professionals and the laboratories is the key to quality reports.

References

Lee A, McLean S. The laboratory report: a problem in communication between clinician and microbiologist? Med J Aust 1977;2:858-860.

Guidelines for Interpreting Numerical Data of Non-viable (Spore Traps) and Viable Airborne Mould Samples

In this article we discuss additional guidelines for interpreting numerical data for viable and non-viable airborne mould samples.

Air-O-Cell cassette for air sampling
Air-O-Cell cassette for air sampling

The guidelines may be used to decide whether further investigations are required after initial investigations. However, numerical laboratory results cannot be used as the primary determinant of whether there is a mould problem but should always be used together with visual inspection data and other available information such as the building history. See our course How To Interpret Mold Results.

Generally, indoor airborne mould concentrations are compared with those of outdoor. The presence of one or more species of mould indoors, but not outdoors, suggests presence of a growth source in the building. This comparison may not be possible during winter since outside concentrations may be below the detection limits as mould growth is slowed by the cold weather. The same principles for comparing outside with indoor can be used to compare the test rooms with the control rooms.

These guidelines are mainly summarized from those developed by the German Federal Environmental Agency (Umweltbundesamt, 2002) and the Health Canada (Indoor Air Quality in Office Buildings: A Technical Guide, 1993).

Guidelines for Interpretation of Numerical Data of Non-viable Mould Air Samples

For a comprehensive assessment of the sample results, all the six steps require to be followed where applicable.

  1. Consider the concentrations of spore types which may reach high concentrations in the outside environment (for example Ascospores, Alternaria/Ulocladium, Basidiospores, Cladosporium).
    • If the total concentration of these spore types in the indoor air is lower than or equal to 1 to 1.4 times the outside concentration, i.e., Ic ≤ Oc x 1 (+0.4), then indoor source is unlikely (background level).
    • If the total concentration of these spore types in the indoor air is lower than or equal to 1.6 (± 0.4) times the outside concentration, i.e., Ic ≤ Oc x 1.6 (± 0.4), then indoor source is possible and further investigations are required.
    • If the total concentration of these spore types in the indoor air is more than twice the concentration in outside air, i.e., Ic > Oc x 2, then indoor source is likely and immediate further investigations are required.
  1. Consider the concentration of Penicillium/Aspergillus spore types.
    • If the difference in concentration between indoor air and outside air is lower than or equal to 300 spores/m3, i.e., Ic – Oc ≤ 300, then indoor source is unlikely (background level).
    • If the difference in concentration between indoor air and outside air is greater than 300 spores/m3 but lower than or equal to 800 spores/m3 i.e., Ic – Oc > 300 ≤ 800, then indoor source is possible and further investigations are required.
    • If the difference in concentration between indoor air and outside air is more than 800 spores/m3, i.e., Ic – Oc> 800, then indoor source is likely and further investigations are required immediately.

      Chaetomium and Aspergillus spores
      Chaetomium and Aspergillus spores
  2. Consider the concentration of Chaetomium spp.
  •  If the concentration in indoor air is lower or equal to the concentration in outside air, i.e., Ic ≤ Oc, then indoor source is unlikely (background level).
  • If the difference in concentration between indoor air and outside air is lower than or equal to 5 spores, i.e., Ic – Oc ≤ 5, then indoor source is possible and further investigations are required.
  • If the difference in concentration between indoor air and outside air exceeds 5 spores, i.e., Ic – Oc > 5, then indoor source is likely and further investigations are required immediately.
  • Consider the concentration of Stachybotrysspp.
    • If the concentration in indoor air is lower or equal to the concentration in outside air, i.e., Ic ≤ Oc, then indoor source is unlikely (background level).
    • If the difference in concentration between indoor air and outside air is not more than 2 spores, i.e., Ic – Oc ≤ 2, then indoor source is possible and further investigations are required.
    • If the difference in concentration between indoor air and outside air exceeds 2 spores, i.e., Ic – Oc > 2, then indoor source is likely and further investigations are required immediately.
  • Consider the concentration of various other unidentified fungal spores that do not belong to the basidiospore or ascospore types.
    • If the difference in concentration between indoor air and outside air is not more than 400 spores/m3, i.e., Ic – Oc ≤ 400, then indoor source is unlikely (background level).
    • If the difference in concentration between indoor air and outside air is greater than 400 spores/m3 but not more than 800 spores/m3, i.e., Ic – Oc > 400 ≤ 800, then indoor source is possible and further investigations are required.
    • If the difference in concentration between indoor air and outside air is exceeds 800 spores/m3, i.e., Ic – Oc > 800, then indoor source is likely and further investigations are required immediately.
  • Consider the concentration of hyphal fragments.
    • If the difference in concentration between indoor air and outside air does not exceed 150 fragments/m3, i.e., Ic – Oc ≤ 150, then indoor source is unlikely (background level).
    • If the difference in concentration between indoor air and outside air is greater than 150 fragments/m3 but not more than 300 fragments/m3, i.e., Ic – Oc > 150 ≤ 300, then indoor source is possible and further investigations are required.
    • If the difference in concentration between indoor air and outside air exceeds 300 fragments/m3, i.e., Ic – Oc > 300, then indoor source is probable and further investigations are required immediately.

Guidelines for Interpretation of Numerical Data of Viable Airborne Mould Samples

These will be covered in Part II of this article. Or feel free to visit our homepage to view more mould and bacteria testing information, resources and services.

References

Health Canada (1993). Indoor air quality in office buildings: a technical guide. A report of the Federal Provincial Advisory Committee on Environmental and Occupational Health. 55 pp.

Umweltbundesamt (2002). Leitfaden zur Vorbeugung, Untersuchung, Bewertung und Sanierung von Schimmelpilzwachstum in Innenräumen. Erstellt durch die Innenraumlufthygienekommission des Umweltbundesamtes.

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