New model highlights key measures in curbing local COVID-19 outbreaks

By Dr. Tomislav Meštrović, MD, Ph.D.Apr 23 2020

A new decision analytical model published in JAMA Network Open by the researchers from China examined a number of vital epidemiological features of imported severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease 2019 (COVID-19) cases in the Chinese city of Wenzhou, emphasizing the need for timely community containment.

Research Letter - Epidemiological Assessment of Imported Coronavirus Disease 2019 (COVID-19) Cases in the Most Affected City Outside of Hubei Province, Wenzhou, China - Image Credit: ImageFlow / Shutterstock

The COVID-19 pandemic has now spread to over 185 countries, with approximately 2.5 million reported cases and more than 170 thousand deaths. However, the start of this global threat in December 2019 can be traced back to Wuhan, the capital of the Chinese Hubei province.

From Wuhan, the disease spread swiftly to other cities, before Wuhan enforced a complete lock-down on January 23, 2020. Outside Hubei province, the most affected Chinese city was Wenzhou in southeastern China, approximately 600 miles from Wuhan, with a population of 9.2 million.

Between January 10 and January 23 in 2020, almost 50 thousand individuals traveled from Wuhan to the coastal city of Wenzhou. To stop the further spread dead in its tracks, a plethora of community containment measures were implemented from January 24, 2020, onwards – including isolation, quarantine, traffic control, and strict social distancing. What was the end-result in curbing the local outbreak?

Steps towards the precise model

In order to obtain precise insights, researchers from the Zhejiang University School of Medicine and Shanghai Normal University decided to develop a decision analytical model that incorporated all confirmed COVID-19 cases reported to the Municipal Health Commission of Wenzhou between January 21 and February 15, 2020.

The susceptible-asymptomatic-symptomatic-quarantined-isolated-removed model was utilized to simulate the dynamic of COVID-19 transmission. The basic reproduction number (R0) was estimated as 2.9 with the use of the exponential growth method, indicating that one case would, on average, produce 2.9 secondary cases in a susceptible population without intervention measures.

In short, such a modeling approach was used to the impact of four different measures on total cumulative COVID-19 case numbers six months later. And indeed, the comparison of simulated and subsequently reported cumulative cases showed that the proposed model mimicked the actual spread rather well.

Valuable epidemiological case study

"Our simulation showed that the intensity and starting time of control and prevention measures had major impacts on the spread of COVID-19", explains study authors in their article.

Their estimates have suggested that the outbreak would gradually vanish in late February and end in early March of 2020 after community containment approaches have been implemented in Wenzhou. Consequently, these anti-COVID-19 measures are now a valuable experience for other places around the world that are battling with this epidemic.

The authors have shown that the total mean cumulative number of COVID-19 cases six months later would decrease to 440 if the quarantine of asymptomatic individuals were increased by 50% from the baseline. Conversely, the mean number of cumulative cases would escalate to 15 576 if measures were delayed for just five days after the first diagnosed case. Such a small margin of error represents the key take-home message.

Emulating a success story in other places

"Our epidemic analysis demonstrated that the timely community containment approaches implemented in Wenzhou were associated with the end of the COVID-19 epidemic in early March 2020", study authors highlight their main finding.

Their message is that quarantining asymptomatic individuals is equally essential as isolating/hospitalizing infected individuals showing overt symptoms. Together with 'highly aggressive' social distancing measures, this was very effective in controlling the spread of SARS-CoV-2.

"A limitation of our epidemic analysis is that it is data-driven and limited by its applicability; however, these data have important implications in forecasting and preventing the potential spread of COVID-19 outbreaks in other countries", say the study authors.

The study concludes with the notion that countries currently tackling severe epidemics should further reinforce epidemiological investigations and increase quarantine measures of close-contact individuals, particularly when medical resources are sparse.