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Review
. 2021 Jan 1;273(1):28-33.
doi: 10.1097/SLA.0000000000004590.

Time-varying Reproductive Rates for SARS-CoV-2 and its Implications as a Means of Disease Surveillance on Lockdown Restrictions

Eman A Toraih  1   2 , Mohammad H Hussein  1 , Rami M Elshazli  3 , Manal S Fawzy  4   5 , August Houghton  6 , Danielle Tatum  7 , Mary Killackey  1 , Emad Kandil  8 , Juan Duchesne  9
Affiliations
Review

Time-varying Reproductive Rates for SARS-CoV-2 and its Implications as a Means of Disease Surveillance on Lockdown Restrictions

Eman A Toraih et al. Ann Surg. .

Abstract

Objective: To quantify the time-varying reproductive rates for SARS-CoV-2 and its implication in Louisiana.

Summary of background data: Basic reproductive number (R0) and effective reproductive number (Re or Rt) are 2 measures of the ability of an infectious agent to spread in the environment. They differ in that R0 assumes zero immunity in the population, while Re or Rt accounts for change over time. Reproductive number modeling is influenced by several factors, including serial interval, the time between the onset of symptoms in an infector, and a secondary case. Quantification of the ability of a pathogen to spread is essential in guiding policy.

Methods: Here, we construct epidemic curves and calculate daily Rt values for the state of Louisiana and each of its 9 regions.

Results: Our results demonstrated variation over both time and geography in calculated R0 and Rt values. Generally, as time has progressed, predicted R0 and Rt values have decreased. In Louisiana, mean Rt was calculated at 3.07 in March and 0.82 by May. A reproductive number less than one is important as it indicates infectious spread will decline with time. The most recent finding of mean Rt = 0.82 is important. It stands in stark contrast to the situation in April when New Orleans, Louisiana, had the highest per capita coronavirus mortality rate in the United States - twice that of New York City and 4 times the rate in Seattle.

Conclusion: As locations around the world begin to lift restrictions, monitoring of infectious spread will be essential.

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Conflict of interest statement

The authors declare no conflict of interests.

Figures

FIGURE 1
FIGURE 1
Pooled analysis for the serial interval. Last name of the first author, date of publication, and the geographical region of the affiliated authors. Each navy line represents the values for a study, plotted as effect size and confidence interval. Raw values are shown as mean and standard deviation reported in each study. The green diamond represents the pooled estimate for the 14 studies. Between-studies homogeneity was observed since I2 was below 50%.
FIGURE 2
FIGURE 2
Estimation of time-varying reproduction number in Louisiana. A, Timeline for mitigation measures in association with epidemic curve. X-axis represents the time and Y-axis shows the daily incidence of new cases. B, Map of Louisiana colored according to cumulative incidence on May 10. C, Time-varying reproduction number in Louisiana from March 14 to May 10. Estimates decline from 3.07 before mitigation measures to 0.82 by the end of the study period.
FIGURE 3
FIGURE 3
Epidemic curves for daily incidence rates. Graph shows daily confirmed new cases by day through May 10, representing in the 9 regions of Louisiana. Horizontal x-axis shows the date of illness onset among cases and the vertical y-axis shows the number of cases.
FIGURE 4
FIGURE 4
The estimated time-varying reproductive number across 9 regions during the study period from March 14 to May 10, 2020. Horizontal x-axis shows the date of illness onset among cases and the vertical y-axis shows the value of time-varying reproduction rate Rt. The first and last estimated Rt is presented. Red font for Rt > 1.0 while green is for Rt < 1.0.
FIGURE 5
FIGURE 5
The estimated reproductive number across parishes. A, Map for 9 regions of Louisiana. B, Effective reproductive rate in Louisiana, 9 regions, and 64 Parishes during the study period from March 14 to May 10, 2020.
See this image and copyright information in PMC

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