People with travel links to China, Iran, and Italy accounted for nearly two-thirds of initial Covid-19 cases outside mainland China in the pre-pandemic period between December 31 and March 10, a new study in the medical journal Lancet says.
The study is the first of its kind to use publicly available global case data to describe travel exposure and case cluster characteristics among early Covid-19 cases in different countries, revealing where the first cases of Covid-19 outside China may have originated based on case travel histories. The study also found four large clusters and outbreaks triggered in different countries to be linked with “transmission in faith-based settings”.
The novel coronavirus was first detected in the central Chinese city of Wuhan in Hubei province late last year before spreading within China and then triggering the worst global pandemic in recent histories. Scientists have been researching how the virus rapidly spread outside China March onwards when the World Health Organisation (WHO) declared it a pandemic.
Also read: China logs another 105 Covid-19 cases in new surge, silent about virus link in Xinjiang
The new study published on Wednesday in The Lancet Infectious Diseases journal compiled publicly available information from the pre-pandemic period until March 10, the day before when the WHO declared it a pandemic.
“Of the first confirmed Covid-19 case in each affected country outside mainland China, almost two-thirds had travel links to Italy, China, or Iran. Study suggests 1 in 4 of these first cases originated in Italy, and 1 in 5 in China,” the researchers found.
The study said that many small clusters of household transmission were reported among early cases but clusters in occupational and community settings tended to be larger—supporting the role of physical distancing to slow the spread of Covid-19. The researchers went through available data from 99 countries including India.
As much as three-quarters or 75 countries outside mainland reported the first Covid-19 case in people who had “…recently travelled to an affected country—with almost two-thirds of these first cases linked to travel to Italy (27%), China (22%), or Iran (11%),” according to the new research. Incidentally, in January, the first two confirmed cases of Covid-19 – then only known as an unidentified strain of coronavirus – were reported in South Korea and Thailand, both with travel history to Wuhan in central China.
In India, the first three Covid-19 cases were diagnosed in three students who had returned from Wuhan in the first evacuation flight launched by New Delhi.
“Our findings suggest that travel from just a few countries with substantial SARS-CoV-2 transmission may have seeded additional outbreaks around the world before the characterisation of Covid-19 as a pandemic on March 11, 2020,” says Dr Fatimah Dawood from the Centers for Disease Control and Prevention (US CDC), who co-led the research.
“In this study, researchers examined publicly available online reports from national ministries of health and other government agency websites, social media feeds, and press releases on a daily basis to identify newly confirmed cases of Covid-19 reported between December 31, 2019, and March 10, 2020 (ie, during the pre-pandemic period, corresponding to weeks 1-11 of the outbreak).”
During the first 11 weeks of the Covid-19 outbreak, 32,459 Covid-19 cases were identified from 99 countries and locations outside mainland China.
“Travel to Italy was linked with half (3/6 cases) of the first-reported cases in Africa, and over a third (36%, 16/45) in Europe and the Americas (38%, 5/13). Travel to mainland China accounted for 83% (10/12) of the first reported cases in the Western Pacific and over half (57%, 4/7) in Southeast Asia.”
Seven or 44% of the first reported cases in the Eastern Mediterranean region had a history of travel to Iran. Analysing the data, the researchers found that household transmission was reported in three-quarters (76/101) of clusters, with an average of 2.6 cases in each cluster.
“By contrast, the 11 clusters related to community gatherings (ie, tour groups, faith-based groups, and dinner parties; average 14.2 cases per cluster), and the 14 clusters reported in non-health-care occupational settings (average 4.3 cases per cluster), tended to be larger—supporting a possible role for physical distancing in slowing the spread of Covid-19,” researchers said.
One of the authors suggested the importance of coordinating with religious groups in preventing cluster infections.
“Four large clusters in our analysis, and large outbreaks reported elsewhere, have been linked with the transmission in faith-based settings, highlighting the need to partner with faith-based organisations when designing and implementing community mitigation efforts,” said co-author Dr Philip Ricks from the US CDC.
Limitations of the study include the fact that the first confirmed case in each country might not have been the first true case of infection in some countries, since early case detection efforts varied substantially.
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