Abstract:
The study done in Mumbai which correlates the burden of tuberculosis to
architectural parameters in resettlement colonies, published in the
Journal Cities & Health (03/2020) is a very useful and timely study.
For further studies in this area, a refinement is needed in the
measurement and calculation of the Natural ventilation in the built
spaces. The study in question uses anemometer to measure the air
velocity and Computational fluid dynamics to validate the ventilation,
but assumes it to be only wind driven. This article looks at the
possibility of more accurate methods and inclusion of infection risk
assessment models. (99 words)
Keywords : Airborne Infection Control; Infection Risk Assessment
Models; Tuberculosis; Architecture; Tracer gas method; Wells-Riley
Model.
Tuberculosis is a deadly disease with alarming numbers in
India.[1-3] has a key role to play in prevention of the spread of
diseases like Tuberculosis.[4] The study published in Cities and
Health journal titled ‘Association between architectural parameters and
burden of tuberculosis in three resettlement colonies of M-East Ward,
Mumbai, India’[5] is a very good effort by the authors and
researchers. They have performed this study in Mumbai which is a very
densely populated city in India. The spread of airborne diseases, TB in
case of the mentioned study, is crucial and has been well studied in
relation to the architectural parameters in the said study.
There is one concern that can be pointed out to enhance the scholarship
in this study for future studies in India and across the world. The
method of measuring ventilation in the households under study needs to
be improved for future studies in this area. The study has used two
methodologies in combination to find out the rate of ventilation in the
households in question. One method uses an anemometer to measure the
wind velocity for 10 minutes in 60 households out of the 4080 households
for which the questionnaire based study was done in the study. The
velocity was measured in this study, to compare it with the results of
the questionnaire based survey and correlate a relation between
ventilation and disease spread. The use of only anemometer based wind
velocity measurements in this study has certain key problems as they
don’t account for the leakages in the space and miss out on the
ventilation that may happen due to the diffusive movement of the air, in
the absence of wind speeds below the measurable rate of the anemometer.
Another very important point that may need attention is the absence of
any further processing of the air velocity to the probability of
infection as has been widely done by the Wells-Riley[6] model based
on the ACH(Air changes per hour) of the building. Apart from the above
mentioned model, there are multiple other models which can be used for
such correlation.[7] The approximate ACH can easily be calculated
using the air velocity at the openings of the spaces using a basic
anemometer or a vaneometer [8]. A previous baseline study done in
2015 [9] in India also used the air velocity to access the ACH in
Tuberculosis facilities in India. They pointed the use of only air
velocity measurement as a limitation as other methods of higher
reliability like tracer gas method could not be used. The study in
question [5] has repeated this that too incompletely as ACH (Air
Changes per hour) was not found out. Though the study in question also
has listed the study done in South Africa [10] but they have not
used the Rudnick Milton Model to correlate the ventilation with the
spread of tuberculosis in the households mentioned. Multiple studies
performed across the world have performed ventilation calculations based
on the Air change rate. [11-12] Even when they measured the air
velocity, it was done to eventually find the ACH by calculation. The air
changes into a built space have a key role to play in diluting the
presence of the airborne particles and have been reliably shown to
decrease the probability of infection in the case of Tuberculosis. Other
studies have used the Rudnick Milton Equation to find out the
probability of infection using the rebreathed air, which is also a
surrogate for the ventilation in the space.[13] There are multiple
studies [10, 14-15], which have attempted to relate ventilation to
the spread of airborne infection and have used the Rudnick Milton Model.
The study in total is a great attempt and is needed in India where very
few studies are done with the level of work put in by the authors of the
study in question. The observation was submitted to the editor of the
journal to which it was published. The editor encouraged and accepted
the suggestions, but did not publish the observation as a letter to the
editor. The reviewer responded that ‘although the method you describe is
very accurate, the resources required would be considerable for the
number of properties involved in this study, moreover, the method your
propose would not have much influence on the overall conclusion. As a
highly technical response we do hope you take your response and this
expert review and maybe publish in a journal that deals more
specifically with these more technical measurement issues, whilst also
addressed the comment’ But in order to increase the scholarship in this
area, it is required to provide further inputs for future studies.
Natural Ventilation and its correlation have been done worldwide on the
basis of the Infection probability models. The current study could have
compared their results to the models in order to strengthen their case
and validate their results. On the contrary, in case of different
results, they could have used this to contribute further to the models
with the inputs they have found in their study. The use of tracer gas
method or the Carbon dioxide measurement to calculate the ventilation by
surrogate method could also have been used for accuracy, as compared to
air velocity measurements or CFD studies where ventilation has been
assumed to be only wind-driven.
Notes:
1. The author and the co-author have no conflict of interest.
2. Authors Contribution as per CRediT
Ar. Raja Singh: Conceptualization, Formal Analysis, Writing-Original
draft
Prof. Dr. Anil Dewan: Supervision, Validation
3. No funding was received for this study
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