The joint study, entitled "The early phase of the COVID-19 outbreak in Lombardy, Italy," analyzed a total of 5,830 laboratory-confirmed cases with symptoms onset from January 14 to March 8, to see how the epidemic developed in Lombardy, the epicenter in the country.

The COVID-19 epidemic in Italy started long before February 20 when the first case was confirmed in the country, according to a study submitted to arXiv, a preprint paper platform on March 20.

It found the epidemic there "started much earlier than February 20, 2020."

"At the time of detection of the first COVID-19 case, the epidemic had already spread in most municipalities of Southern-Lombardy," the article said.

From the epidemiological data collected by the researchers, the median age of the cases is 69 years old, and 47 percent of the patients who tested positive were hospitalized, among which 18 percent required intensive care.

The mean serial interval – the time between successive cases, is estimated to be 6.6 days, and the reproduction number (RO) of the virus to be 3.1, which means one infected person can spread the infection to over three.

There is no significant difference in the viral loads in nasal swabs between the symptomatic and asymptomatic, said the researchers, who cautioned that COVID-19 has a "very high" transmission potential and "the number of critical cases may become largely unsustainable for the healthcare system in a very short-time horizon."

The study called for "aggressive containment strategies" to control the disease spread and "catastrophic outcomes for the healthcare system."

Over 92,000 cases had been confirmed in Italy as of Saturday.