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    Review of 'Normal background levels of air and surface mould reserve in UK residential building stock'

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    Normal background levels of air and surface mould reserve in UK residential building stockCrossref
    This study gives the readers a snapshot of air-borne and surface fungal levels in the UK
    Average rating:
        Rated 3.5 of 5.
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        Rated 4 of 5.
    Level of validity:
        Rated 3 of 5.
    Level of completeness:
        Rated 3 of 5.
    Level of comprehensibility:
        Rated 3 of 5.
    Competing interests:
    None

    Reviewed article

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    • Abstract: found
    • Article: found
    Is Open Access

    Normal background levels of air and surface mould reserve in UK residential building stock

     Yasemin Aktas (corresponding) ,  Morten Reeslev,  Héctor Altamirano (2019)
    This paper reports results obtained from a surface (both visually clean and dirty/dusty surfaces) and active (aggressive) air testing scheme on 140 residential rooms in England, without visible water damage or mould growth, along with a few rooms with visible mould growth/water damage tested for comparison purposes, with the aim of providing background levels of mould in non-water-damaged interiors to benchmark a normal indoor environment, and in turn when there is a need for further investigation, and, possibly, remediation. Air and surface mould was quantified based on the activity of β-N-acetylhexosaminidase (EC 3.2.1.52; NAHA). The obtained readings showed a log-normal distribution. 98% of the samples obtained from visually clean surfaces were equal to or less than 25 relative fluorescence units (RFU), which is suggested to be the higher bound for the range which can be used as a success criterion for surface cleaning/remediation in non-problem buildings. Of samples obtained from visually dirty/dusty surfaces, around 98% were below 450 RFU, which is suggested to define the lower-bound for abnormally high levels of mould, rare even on dirty/dusty surfaces. Similarly, around 98% of the air samples were found to have 1700 RFU or below. Values above 1700 RFU are therefore unlikely in a non-problem indoor environment and can be indicative of a possible problem inducing mould growth. The samples with values below 1700 were further divided into three proposed sub-categories. Finally, these values were compared to those obtained in Denmark in a similar study and are currently used in national standards, and they were found highly congruent, suggesting that local climate regimes and room functions might not be as influential on indoor mould levels, or that the nuances between UK and Denmark in terms of these factors are not strong enough to lead to sizable changes in the typical indoor mould levels in these countries.
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      Review information

      10.14293/S2199-1006.1.SOR-ENG.AMHGWZ.v1.RVVXKR

      This work has been published open access under Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com.

      ScienceOpen disciplines:
      Keywords:

      Review text

      This study aimed to establish a baseline level to differentiate whether an indoor environment is considered ‘normal’ or ‘problematic’ as an early indication for remediation. The author has also stated the limitations to perform such interpretation such as lack of a scientifically driven standard/values/cut-off points, and there is no consensus on the present values suggested by certain institutions. As in common practice, remediation is performed where by fungal growths are visible, and concerns raised by the occupants of possible health effects as well as aesthetics value. This study gives the readers a snapshot or cross-section of air-borne and surface fungal levels in selected normal UK residential buildings, although there are a few important points to be considered to add significant values to the manuscript.

      General

      References – need to standardised the format according to the journal format, either numbering or alphabetical order in the list of references.

      It is recommended to add in more references to make it more relatable with current research and monitoring of indoor moulds, and how this study is important to fill those gaps. 

      Introduction:

      Page 2:

      Line 2: Problem of mould in the UK – is that associated with indoor environment in general or only with water intrusion, damped environment? It is best to state a prevalence rate and references to support this statement.

      Line 6: Is ‘acceptable mould level’ refers to only airborne fungi? Or does it give weightage to common clinically important fungi which can brings effects on health or mycotoxin producers? Is there a way to address this from previous study or is it still a research gap?

      Line 7: Is the baseline level indoors also correlates with the mould levels outdoors, since seasonal variations may also play a role in the fluctuations of fungal spores in both outdoor and indoor air? Maybe, could add in reference(s) from previous studies?

      Line 13: This is correct that no visible moulds does not mean moulds are not present. Microorganisms are ubiquitous in the environment, and we are living in a non-sterile environment.

      Line 26: The mould concentrations were measured using NAHA expressed in RFUs.

      To add in more references/background on NAHA why this method is a way forward to be used as a marker of mould contamination.

      It is important to know what are the advantages or disadvantages of this method as compared to other widely used methods, as a strong basis on why this method is preferred and more/equally reliable.

      Is there side-by-side comparison and correlation with widely used method of media plate/filter attached to air-sampler expressed in CFUs? Any reference(s)?

       

      Does the RFU correlates to culturable method or non-culturable method such as PCR? Any reference(s)?

      How specific is the method to capture the enzymatic activity of only moulds and not other contaminants?

      Materials and methods:

      Page 2: Line 1: A total of 140 non-water-damaged rooms with no visible mould were sampled. How did the study sites were selected? Could the sample size infer/ represent the UK residential buildings? Or, was it a survey of selected buildings?

      How long was the duration of the study, and do you think that environmental factors (confounding factors) such as seasonal variations, humidity level, and types of ventilation might affect the results?

      Results and discussion:

      Page 4:

      Is this a separate section from ‘Discussion’?

      To use clear terms. ‘Samples containing mould growth’……. Does it referring to growing moulds in culture media from the samples to confirm presence of culturable mould or does it refer to as ‘no visible mould growth at the sites’?

      Missing link of figure (appears as error)

       

      Page 5:

      Figure 1: Missing word ‘98% of all samples from clean…...the UK and'

      The RFU reading (x-axis) was grouped into nine scales. On what basis each cut-off of RFUs (2.7, 7.4. etc) and cut- off of 25 and 450 were chosen? Any reference(s)?

      To include error bars (range, mean or median)

      Page 6:

      Figure 2: To include error bars (range, mean or median)

      Same as Fig 1, why the cut-off points were chosen?

      Discussion:

      Page 7: Is this part of section 3?

      Conclusions:

      Some parts sound good as discussion. 

      Comments

      Dear Zuraifah,

      Many thanks for reviewing our paper and apologies for our delayed response.

      Please see below our responses to your individual comments:

      • Line 2: Problem of mould in the UK – is that associated with indoor environment in general or only with water intrusion, damped environment? It is best to state a prevalence rate and references to support this statement.

      Problem of mould in the UK, as in many other locations, have been found linked with escape of water, climatic conditions and hazards (e.g. flooding, driven rain and the like), poor management of indoor conditions including insufficient ventilation and fuel poverty. We have outlined this very briefly and added references.

      • Line 6: Is ‘acceptable mould level’ refers to only airborne fungi? Or does it give weightage to common clinically important fungi which can brings effects on health or mycotoxin producers? Is there a way to address this from previous study or is it still a research gap?

      Acceptable mould level refers in most guidance to airborne fungi as these documents are more focussed on the health implications of mould and the amount of airborne fungal agents is considered as the most representative of potential exposure. In our study we also address the acceptable surface mould issue, as in the common or “normal background” levels of mould.

      • Line 7: Is the baseline level indoors also correlates with the mould levels outdoors, since seasonal variations may also play a role in the fluctuations of fungal spores in both outdoor and indoor air? Maybe, could add in reference(s) from previous studies?

      We have now added a paragraph (third paragraph of the Introduction) on the indoor-outdoor comparison, and comments on seasonality to the discussion.

      • To add in more references/background on NAHA why this method is a way forward to be used as a marker of mould contamination. It is important to know what are the advantages or disadvantages of this method as compared to other widely used methods, as a strong basis on why this method is preferred and more/equally reliable. Is there side-by-side comparison and correlation with widely used method of media plate/filter attached to air-sampler expressed in CFUs? Any reference(s)? Does the RFU correlates to culturable method or non-culturable method such as PCR? Any reference(s)? How specific is the method to capture the enzymatic activity of only moulds and not other contaminants?

      More info and references on the method have been added to the end of the Introduction.

      • Page 2: Line 1: A total of 140 non-water-damaged rooms with no visible mould were sampled. How did the study sites were selected? Could the sample size infer/ represent the UK residential buildings? Or, was it a survey of selected buildings? How long was the duration of the study, and do you think that environmental factors (confounding factors) such as seasonal variations, humidity level, and types of ventilation might affect the results?

      The studied buildings were made available to us by volunteers. We have confidence that our selected building set is able to reflect a meaningful representation of English building stock thanks to its randomness in terms of several key parameters including location, construction type, age and occupancy types, while the preliminary nature of this examination being reserved.

      We thank the reviewer for this comment especially, as it made us revisit our title, which has now been changed as the “(…) in English residential building stock (…)” from “(…) in UK residential building stock (…)”. The manuscript has also been revised to reflect this change.

      For a detailed account of how humidity and ventilation might have influenced the mould readings in some of our tested rooms please see Aktas et al., 2018a. As per the seasonality, we have not differentiated our analyses based on that, however the stark similarity between our suggested thresholds for England and Denmark may suggest some level of disassociation between normal background levels and seasons. We agree that this should be looked into more deeply by future research however, and we have now added this point to our discussion section.

      • To use clear terms. ‘Samples containing mould growth’……. Does it referring to growing moulds in culture media from the samples to confirm presence of culturable mould or does it refer to as ‘no visible mould growth at the sites’?

      This phrase has now been replaced as “samples identified by microscopy analysis that did not contain mould growth” to avoid confusion.

      • Missing link of figure (appears as error)

      This has now been fixed.

      • Figure 1: Missing word ‘98% of all samples from clean…...the UK and'

      This has now been fixed.

      • The RFU reading (x-axis) was grouped into nine scales. On what basis each cut-off of RFUs (2.7, 7.4. etc) and cut- off of 25 and 450 were chosen? Any reference(s)?

      The values are as such because this is an exponential axis. This has now been clarified. The axis has been further amended to show the ranges more clearly.

      • Page 7: Is this part of section 3?

      Now the results and discussion have been collated under the same section to avoid confusion.

       

      2020-02-12 13:19 UTC
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