The novel coronavirus SARS-CoV-2 was in Northern Italy as early as 1 January.
An epidemiological analysis of Lombardy, the epicentre of the outbreak in Italy, reveals that the first onset of symptoms in the country occurred weeks before the disease was reported there on 20 February. The study looks at nearly 6,000 laboratory-confirmed cases to track how the outbreak unfolded in the region. It was posted to the arXiv preprint server on 20 March.
The undetected spread in January is “very striking”, says Michele Tizzoni, an infectious disease modeller at the ISI Foundation in Turin, Italy, who was not involved in the work. “At that time we were probably still talking about Wuhan.”
Instead, by the time the first case was detected in Italy, the virus had already spread to most towns and cities in Southern Lombardy. Over the next several weeks, nearly half of the patients who tested positive for COVID-19 were hospitalised; about one-fifth of those required intensive care.
The new picture of the outbreak in Lombardy makes it clear that “aggressive containment strategies are required” to stop the spread of the virus, the authors write. Although public activities and gatherings in the region were banned just 3 days after the first positive test, the undetected spread in the weeks prior meant that the virus had already taken hold, with cases doubling roughly every 3 days.
These data will be vital to other countries and public health organisations getting ready to face their own outbreaks of the pandemic, Tizzoni says. His advice to them? “Be prepared. Even if you don’t see much.”
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