The novel coronavirus SARS-CoV-2 was present 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 COVID-19, the disease caused by the virus, 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.Covert coronavirus infections could be seeding new outbreaks
The undetected spread in January is “very striking”, says Michele Tizzoni, who models infectious diseases at the ISI Foundation in Turin, Italy, but 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 hospitalized; 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 three days after the first positive test, the virus’s undetected spread in the previous weeks meant that it had already taken hold, with the number of cases doubling roughly every three days.
These data will be vital to other countries and public health organizations 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.”