Investigation of air change rate and aerosol behavior during an outbreak of COVID-19 in a geriatric care facility

  1. Yo Ishigaki
  2. Shinji Yokogawa
  3. Yuki Minamoto
  4. Akira Saito
  5. Hiroko Kitamura
  6. Yuto Kawauchi

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Abstract

Background

Ventilation plays an important role in controlling aerosol transmission of coronavirus disease (COVID-19), and mass transmission of COVID- 19 has been reported in poorly ventilated areas.

Objective

A real-world mass infection outbreak which occurred in an elderly nursing home, in Miyagi Prefecture, Japan, was simulated experimentally and numerically to investigate the controlling factors and quantify the effectiveness of various natural ventilation settings by means of air change rate (ACR).

Methods

Using the CO 2 tracer gas method, the ACR values at the time of the outbreak were estimated to be 2.0–6.2 h -1 in rooms in the facility. Furthermore, a low-cost intervention of opening windows improved the ventilation frequency by a factor of 1.48–5.74. This implies that advective fluid flows are the key in the spread of high CO 2 concentration zones. A numerical simulation was performed to obtain spatio-temporal evolution on such high CO 2 concentration zones under similar conditions to the present experiment.

Results

The results showed that ventilation was significantly dependent on the window opening conditions in all rooms (p-values ranging from 0.001 to 0.03 for all the rooms). In contrast, there was no significant dependence on the location of the sensor in any of the areas. Development of high CO 2 concentration zones occurs in the first few minutes. Furthermore, the leading edge of such zones towards the common room yields a relatively high fluid velocity, suggesting that the large-scale advective flow dictates the spread of such high CO 2 concentration zones.

Conclusions

The present results suggest that secondary infections could occur due to the aerosol advection driven by such large-scale flows, even when the building design adheres the ventilation guidelines. In elderly care facilities, open architectural spaces are recommended to realize quality of life and monitor residents. However, management is required to reduce the downwind infection risk from aerosols and ACR.

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  1. Version published to 10.1101/2022.01.27.22269512v2 on medRxiv
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    SciScore for 10.1101/2022.01.27.22269512: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: Please consider improving the rainbow (“jet”) colormap(s) used on page 31. At least one figure is not accessible to readers with colorblindness and/or is not true to the data, i.e. not perceptually uniform.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

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  3. Version published to 10.1101/2022.01.27.22269512v1 on medRxiv