Comparison of infection control strategies to reduce COVID-19 outbreaks in homeless shelters in the United States: a simulation study

  1. Lloyd A. C. Chapman
  2. Margot Kushel
  3. Sarah N. Cox
  4. Ashley Scarborough
  5. Caroline Cawley
  6. Trang Q. Nguyen
  7. Isabel Rodriguez-Barraquer
  8. Bryan Greenhouse
  9. Elizabeth Imbert
  10. Nathan C. Lo

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Abstract

Background

COVID-19 outbreaks have occurred in homeless shelters across the US, highlighting an urgent need to identify the most effective infection control strategy to prevent future outbreaks.

Methods

We developed a microsimulation model of SARS-CoV-2 transmission in a homeless shelter and calibrated it to data from cross-sectional polymerase chain reaction (PCR) surveys conducted during COVID-19 outbreaks in five homeless shelters in three US cities from March 28 to April 10, 2020. We estimated the probability of averting a COVID-19 outbreak when an exposed individual is introduced into a representative homeless shelter of 250 residents and 50 staff over 30 days under different infection control strategies, including daily symptom-based screening, twice-weekly PCR testing, and universal mask wearing.

Results

The proportion of PCR-positive residents and staff at the shelters with observed outbreaks ranged from 2.6 to 51.6%, which translated to the basic reproduction number ( R 0 ) estimates of 2.9–6.2. With moderate community incidence (~ 30 confirmed cases/1,000,000 people/day), the estimated probabilities of averting an outbreak in a low-risk ( R 0 = 1.5), moderate-risk ( R 0 = 2.9), and high-risk ( R 0 = 6.2) shelter were respectively 0.35, 0.13, and 0.04 for daily symptom-based screening; 0.53, 0.20, and 0.09 for twice-weekly PCR testing; 0.62, 0.27, and 0.08 for universal masking; and 0.74, 0.42, and 0.19 for these strategies in combination. The probability of averting an outbreak diminished with higher transmissibility ( R 0 ) within the simulated shelter and increasing incidence in the local community.

Conclusions

In high-risk homeless shelter environments and locations with high community incidence of COVID-19, even intensive infection control strategies (incorporating daily symptom screening, frequent PCR testing, and universal mask wearing) are unlikely to prevent outbreaks, suggesting a need for non-congregate housing arrangements for people experiencing homelessness. In lower-risk environments, combined interventions should be employed to reduce outbreak risk.

Article activity feed

  1. Version published to 10.1186/s12916-021-01965-y
  2. Version published to 10.1101/2020.09.28.20203166v4 on medRxiv
  3. Rapid Reviews Infectious Diseases

    Fiona Walsh

    Review 2: "Comparison of infection control strategies to reduce COVID-19 outbreaks in homeless shelters in the United States: a simulation study"

    Reviewers find this study a generally reliable and important contribution to understanding infection control strategies in a high-risk setting, though several assumptions in the model could be clarified.

  4. Rapid Reviews Infectious Diseases

    Gregory Karelas

    Review 1: "Comparison of infection control strategies to reduce COVID-19 outbreaks in homeless shelters in the United States: a simulation study"

    Reviewers find this study a generally reliable and important contribution to understanding infection control strategies in a high-risk setting, though several assumptions in the model could be clarified.

  6. Version published to 10.1101/2020.09.28.20203166v3 on medRxiv
  7. Version published to 10.1101/2020.09.28.20203166v2 on medRxiv
  8. ScreenIT

    SciScore for 10.1101/2020.09.28.20203166: (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: Thank you for sharing your code and data.

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    This study has a number of limitations. Due to limited data availability, we only calibrated the model to a small number of shelter outbreaks, the R0 estimates for which are likely to be higher than for the average shelter since they occurred early in the pandemic and larger outbreaks are more likely to be reported. The cross-sectional aggregate nature of the majority of the data also led to wide uncertainty intervals around the fitted parameters, without independent identifiability between them (Additional file 1: Figure S10). Our results suggest that universal masking would significantly reduce the risk of outbreaks in homeless shelters, even with 60% compliance. However, the impact of masking is highly sensitive to the assumed masking effectiveness and compliance, estimates for which still vary considerably despite accumulating evidence that masks reduce infection risk [60–64]. Many uncertainties in the biology of SARS-CoV-2 transmission remain, particularly regarding differential infectiousness over time and by severity of illness, and the relationship of PCR positivity and infectiousness [22,65,66]. Our assumption of equal infectiousness for different individuals means that our model is unlikely to fully reproduce super-spreading events [38,40]. We made several simplifying assumptions in modelling transmission within the shelter and from the surrounding community, namely: homogenous mixing within the shelter population, no entry of new people, a stable background infecti...

    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: We did not find any issues relating to colormaps.

    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.

    About SciScore

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  9. Version published to 10.1101/2020.09.28.20203166v1 on medRxiv