Analysis of COVID-19 spread from China, Italy and Iran

A recent study looked at the patterns of the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from China, Iran, and Italy to other nations. The study by researchers at Case-Western Reserve University School of Medicine and Duke University is published on the preprint website medRxiv* in September 2020.

What was this study about?

The COVID-19 pandemic has claimed over nine hundred thousand lives around the world and infected over 29 million individuals. The SARS-CoV-2 virus was first detected in Wuhan, China, in late December 2019, from where it rapidly spread around the world. SARS-CoV-2 is highly contagious and rapidly spreads from one person to another.

In this new study, the researchers looked at exported COVID-19 cases by country and the time taken between entry until case confirmation for the exported cases using publicly available data.


The spread of the infection was facilitated by international travel, wrote the researchers. China imposed a lockdown in Wuhan on January 23rd, 2020, when the number of cases was rising. Despite the lockdown and prevention of travel across states or out of the country, over 100 SARS-CoV-2 cases were exported out of China by February 14th, wrote the researchers. As the lockdown came into effect, there was significant prevention of virus export, but still, some cases of undetected community spread continued out of China.

South Korea, Italy, and Iran

By February 2020, a large number of cases were reported in South Korea, Italy, and Iran. There was a rapid local transmission of the infection as well as wider international spread.

By mid-March, over 80 nations had reported the outbreak, and the World Health Organization (WHO) declared it a pandemic on March 11th, 2020. The team wrote, “Assuming that the virus did not arise independently in multiple locations, an outbreak of COVID-19 outside of China requires an infected traveler to bring the virus into the country and subsequently infect others.”

This study looked at the rates of export of cases from China, Italy, and Iran, specifically because these nations also recorded the largest outbreaks immediately after the initial outbreak in China. The authors wrote that this would provide “important insight into the spread of the virus through travelers from Wuhan”

What was done in the study?

Data was gathered between January and March 20th, 2020, from published studies, government official statements, credible reports from foreign ministries of health, published news articles available online, etc.

From the data gathered, they organized all those infected into clusters of those that had traveled.  Clusters of travelers ranged in size from 1-17. The average cluster sizes for China, Italy, and Iran were 1.2, 1.2, and 1.9, respectively, the team wrote.

For the clusters, the team included data such as “date of entry of the travelers to their destination country, date of confirmation of COVID-19 of the case, and the estimated size of the affected group.” Further time to diagnosis from travel was also calculated. Graphs were made for dates of confirmation and date of arrival to show the time gap between entry and confirmation for clusters of exported cases of each country. They used a time period of 10 to 14 days from the first reported entry.

What was found?

The key findings of the study were as follows;

  • COVID-19 infected cases left China as early as January 5th, 2020
  • There was an increase in the cluster size of travelers spreading the infection between January 19th, 2020, and January 23rd, 2020. This reduced after the travel ban came into place in Wuhan
  • For exported cases from China, there were twin peaks of cases related to travel on days 3 and day 8 after entry.
  • Infected cases from Italy entered other countries as early as February 15th, 2020
  • The clusters of infected travelers in Italy reached maximum levels on February 29th, 2020. The Italy travel ban was announced on March 9th, 2020, and thus the clusters reduced.
  • For exported cases from Italy, there was a peak of cases related to travel on day 3.
  • From Iran, infected travelers were entering other countries from February 14th, 2020, to March 6th, 2020.
  • Cases began to increase from February 20th until February 27th, 2020.
  • Exports from Iran peaked on February 26th, 2020, then slowly declined
  • For exported cases from Iran, there was a peak of cases related to travel on day 3.
  • The team wrote, “Approximately one-third of all exported cases were confirmed within 3 days of entry suggesting these travelers were mildly symptomatic or symptomatic in arrival.”
  • The authors wrote that the average time between entry of a traveler and confirmation of the case was 7.7, 5.5, and 4.7 days for exports from China, Italy, and Iran, respectively
  • They noted that earlier exported cases (first 10-14 days after the arrival of 1st exported traveler) had a significantly longer time from entry to confirmation compared to later cases for each of the three countries.

Conclusions and implications

The researchers concluded that the exported cases from South Korea were lower than those from China, Italy, and Iran. They call for more careful monitoring and screening of symptomatic travelers with raised public awareness, which can lead to “faster confirmation as well as reduced transmission of COVID-19 pandemic.”

The researchers wrote in conclusion, “This information and analysis can lead to better epidemiological models, more informed decision making about how travel bans affect the exportation of cases, and how best to surveil and test travelers in order to minimize transmission of COVID-19.”

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
  • Exploring Patterns and Trends in COVID-19 Exports from China, Italy, and Iran Ahmed Tamer Soliman, Michael L McHenry, George Luo, Brian Dailey, Toby Chen, John J Letterio medRxiv 2020.09.09.20190983; doi:
Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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