A quarter of the first cases of Covid-19 spotted outside mainland China were people who had traveled to Italy, according to a study published in the medical journal The Lancet Infectious Diseases , which found that the start of the pandemic could be linked to three countries. This work, published this week takes into account the first case recorded in 99 countries outside mainland China during the first 11 weeks of the epidemic (between December 31, 2019 and March 10, 2020): they show that nearly two-thirds (60 %) of these people had traveled to Italy (27%), China (22%) or Iran (11%).
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"Our results suggest that travel to a small number of countries where transmission of the SARS-CoV-2 virus was significant could be the source of epidemics around the world, before the pandemic was declared on March 11. ", said one of the authors, Dr. Fatimah Dawood of the American Centers for Disease Prevention and Control (CDC), quoted in a statement from The Lancet Infectious Diseases .
Important limits
There are, however, important limitations to the study, the researchers point out: the first cases reported in each country may not actually have been the first to exist, as some may have gone unnoticed at first. The study covers 99 countries outside of mainland China, where 32,000 cases were reported during the period between December 31, 2019 and March 10, 2020. To identify the new cases recorded in each country during the period studied, the authors turned to based on online data from the authorities of each country, the daily press releases then disseminated or elements collected on social networks.
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The influence of travel to a particular country on the first cases differs according to the regions of the world. Travel to Italy was linked to half of the first cases spotted in Africa, and more than a third of those spotted in Europe (36%) and the Americas (38%). But in the Pacific area, 83% of the first cases were linked to a trip to China. In total, three-quarters of the first cases spotted in each of the 99 countries were people who had traveled elsewhere before.