July 29 (UPI) -- Almost two-thirds of confirmed COVID-19 cases outside China during early stages of the pandemic occurred among people who had traveled to Italy, China or Iran or to their close contacts, an analysis published Wednesday by The Lancet Infectious Diseases found.
Seventy-five percent of countries outside China that reported their first coronavirus infections during the first 11 weeks of the pandemic -- between Dec. 31, 2019, and March 10 of this year -- could trace the cases to travel to an already affected country, the researchers said.
Of these, 27% were linked with travel to Italy, 22% traced to China and 11% tracked to Iran, they said.
"Our findings suggest that travel from just a few countries with substantial [COVID-19] transmission may have seeded additional outbreaks around the world before the characterization of COVID-19 as a pandemic on March 11," Dr. Fatimah Dawood, a medical epidemiologist at the U.S. Centers for Disease Control and Prevention, said in a statement.
COVID-19 was first identified in Wuhan, China, in December. Italy and Iran were among the first countries outside China to report large-scale outbreaks, according to the World Health Organization.
For this study, Dawood and her colleagues examined publicly available online reports from national ministries of health and other government agency websites, social media feeds and press releases to identify newly confirmed cases of COVID-19.
Countries with at least one case were classified as affected, and "early" cases were defined as the first 100 cases reported in each country, with those after the first 100 referred to as "later" cases, the researchers said.
During the first 11 weeks of the COVID-19 pandemic, 32,459 confirmed cases were reported in 99 countries outside mainland China, they said.
Of 1,200 cases from 68 countries with available patient age or sex data -- 4% of the global number of cases on March 10 -- 874, or 73%, were "early" cases in their respective regions, the researchers said.
Travel to Italy was linked with three of the first six reported cases in Africa, and 16 of the first 45 reported cases in Europe. It also accounted for five of the first 13 cases in the Americas, the researchers said.
Meanwhile, travel to mainland China accounted for 10 of the first 12 reported cases in the Western Pacific region and four of the first seven in Southeast Asia, they said.
Seven of the first 16 reported cases in the Eastern Mediterranean region had a history of travel to Iran, the researchers said.
The average age of people infected in these early cases was 51 years, and only 3% were children younger than 18. Two percent of these early cases were healthcare workers, they said.