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. 2020 Dec 2;20(1):914.
doi: 10.1186/s12879-020-05577-4.

Estimating transmission dynamics and serial interval of the first wave of COVID-19 infections under different control measures: a statistical analysis in Tunisia from February 29 to May 5, 2020

Khouloud Talmoudi  1   2 , Mouna Safer  3   4 , Hejer Letaief  3   4 , Aicha Hchaichi  3   4 , Chahida Harizi  5 , Sonia Dhaouadi  3 , Sondes Derouiche  3 , Ilhem Bouaziz  3 , Donia Gharbi  3 , Nourhene Najar  6 , Molka Osman  3 , Ines Cherif  6 , Rym Mlallekh  6 , Oumaima Ben-Ayed  6 , Yosr Ayedi  6 , Leila Bouabid  3 , Souha Bougatef  3 , Nissaf Bouafif Ép Ben-Alaya  3   4   6 , Mohamed Kouni Chahed  6
Affiliations

Estimating transmission dynamics and serial interval of the first wave of COVID-19 infections under different control measures: a statistical analysis in Tunisia from February 29 to May 5, 2020

Khouloud Talmoudi et al. BMC Infect Dis. .

Abstract

Background: Describing transmission dynamics of the outbreak and impact of intervention measures are critical to planning responses to future outbreaks and providing timely information to guide policy makers decision. We estimate serial interval (SI) and temporal reproduction number (Rt) of SARS-CoV-2 in Tunisia.

Methods: We collected data of investigations and contact tracing between March 1, 2020 and May 5, 2020 as well as illness onset data during the period February 29-May 5, 2020 from National Observatory of New and Emerging Diseases of Tunisia. Maximum likelihood (ML) approach is used to estimate dynamics of Rt.

Results: Four hundred ninety-one of infector-infectee pairs were involved, with 14.46% reported pre-symptomatic transmission. SI follows Gamma distribution with mean 5.30 days [95% Confidence Interval (CI) 4.66-5.95] and standard deviation 0.26 [95% CI 0.23-0.30]. Also, we estimated large changes in Rt in response to the combined lockdown interventions. The Rt moves from 3.18 [95% Credible Interval (CrI) 2.73-3.69] to 1.77 [95% CrI 1.49-2.08] with curfew prevention measure, and under the epidemic threshold (0.89 [95% CrI 0.84-0.94]) by national lockdown measure.

Conclusions: Overall, our findings highlight contribution of interventions to interrupt transmission of SARS-CoV-2 in Tunisia.

Keywords: Coronavirus; Lockdown; Reproduction number; Serial interval; Statistical models; Tunisia.

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Conflict of interest statement

Authors declare no conflict of interest.

Figures

Fig. 1
Fig. 1
Instantaneous effect reproduction number for SARS-CoV-2 by symptom onset date in Tunisia. In the first graph is shown the daily symptom onset time series for coronavirus from February 29, 2020–May 5, 2020. The second graph shows the estimated reproduction number over sliding weekly windows (posterior mean and 95% credible interval, with estimates for a time window plotted at the end of the time window); the blue color is for all cases and the red color is for local cases; the solid lines show the posterior means and the transparent zones show the 95% credible intervals; the horizontal dashed red line indicate the threshold value R = 1
Fig. 2
Fig. 2
Impact of interventions on the estimates of the reproduction number R during the study period in Tunisia. The first intervention was the curfew which is applied on March 18, 2020 and the second one was the national lockdown applied on March 22, 2020
See this image and copyright information in PMC

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