key: cord-1000403-znzyt93x
authors: Wilasang, Chaiwat; Sararat, Chayanin; Jitsuk, Natcha C; Yolai, Noppamas; Thammawijaya, Panithee; Auewarakul, Prasert; Modchang, Charin
title: Reduction in effective reproduction number of COVID-19 is higher in countries employing active case detection with prompt isolation
date: 2020-06-08
journal: J Travel Med
DOI: 10.1093/jtm/taaa095
sha: 33775b490980d617d99783fae7c76c7504d3065d
doc_id: 1000403
cord_uid: znzyt93x

Countries that implemented liberal testing with active case finding and prompt isolation, combined with contact tracing and quarantine, were more successful in reducing the reproduction number compared to countries that primarily relied on social distancing and lockdown measures.

We also calculated the reduction in R t (R t ): a higher R t is indicative of more successful control measures. confidence interval (CI) in 10 selected countries starting from the date at which the number of cumulative confirmed cases in each country exceeds 100 and Figure 1K shows the reduction in R t (R t ) in each country after the control measures have been implemented for 3 weeks. We found that among the selected countries, as of 7 th April 2020, only China and South Korea were successful in controlling the disease: implementing the control measures for 3 weeks, the median of R t decreases more than 2 ( Figure 1K ), and have since remained below or close to 1 ( Figure 1A and 1B).

In China, the epicentre was Wuhan where COVID-19 first emerged in December 2019. By 23 rd January 2020, Wuhan implemented a strict lockdown with a total standstill and stay-at-home policies, combined with contact tracing and quarantining of all contacts. 4 In addition to a strict lockdown, from February onwards, China also added extensive active case finding including isolation of all cases, even mild cases, in Fangcang shelter hospitals. 5 As a result, the median of in China declined from 3.19 (95% CI: 3.11-3.28) to a value lower than the self-sustaining threshold of 1 in approximately 3-4 weeks ( Figure 1A ).

In South Korea, the first COVID-19 case was reported in late January 2020. In contrast to China, South Korea did not implement a strict lockdown but focused on active case-finding with average testing of 12,000 patients per day, with the peak capacity as high as 20,000 tests per day, since 25 th February 2020. 6 The median of in South Korean rapidly decreased from 2.56 (95% CI: 2.38-2.74) to a value lower than 1 in approximately 3-4 weeks ( Figure 1B ). In contrast, by 7 th April 2020, the medians of R t in the United States, United Kingdom, Spain, Iran, Italy, and France were still greater than 1, associated with a much lower R t . 9 , resulting in a lower R t .

Our estimation of R t also has some limitations. First, the estimation of R t was based on the reported case number only. Second, we assumed that testing and reporting were constant over time. Finally, country-to-country comparisons of the effectiveness of control measures are problematic due to many confounding factors, such as different population sizes and densities, superspreading events, social mixing patterns, and nuances in social distancing measures.

Large-scale epidemiological evaluations of the impact of different public health measures dependent on countries` characteristics will be needed in the future. Nevertheless, for the time being, the striking differences of the reduction in the effective reproduction number over a period of 3 weeks in 10 countries show that liberal testing, active case-finding, and prompt case isolation reduce the outbreak size more rapidly. While social distancing led to flattening the curve 10 , only those countries implementing active case detection with prompt isolation experienced a rapid reduction in the reproduction number associated with bending the epidemic curve. Although lockdowns will be necessary when healthcare systems are overwhelmed, the lesson is that basic public health measures that include active case detection with prompt isolation (not just home isolation) 9 need to be strengthened in all countries in order to effectively curb outbreaks in a timely manner.

This project was financially supported by the National Science and Technology Development Agency, Thailand (PO20008199). The funders had no role in study design, data collection, and analysis, decision to publish, or preparation of the manuscript.

CM, PT, and PA conceived and designed the study. CW, CS, NCJ, NY, and CM conducted the study and drafted the manuscript. All authors were responsible for analyses and data interpretation.

The authors declare that they have no conflict of interests. 

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