Silent spread of novel coronavirus in Italy went undetected for weeks

By the time the first case was reported, the virus had already spread to most areas in southern Lombardy

Italy reported its first laboratory-confirmed case of novel coronavirus (SARS-CoV-2) on February 20. But according to a study posted in a preprint repository arXiv, people appear to have been infected in early January and started showing symptoms by January 14. There apparently seems to have been a silent spread of the virus in the community for nearly 50 days.

By the time the first case was reported, the virus had already spread to most areas in southern Lombardy. Lombardy region, a district of 10 million, is the epicentre of the epidemic in Italy. So a day after the first case was reported, 28 more cases were confirmed, confirming the silent spread of the virus in the community.

Uncovering the trail

Contact tracing and testing of both symptomatic and asymptomatic exposures to positive cases helped uncover the ongoing transmission prior to the laboratory confirmation of the first case. The median age of people infected by the virus is 69 years and 47% of people who were infected required hospitalisation, of which 18% required intensive care. Each infected person spread it to 3.1 people, which started decreasing by end of the third week of February. The time between successive cases in the transmission chain, otherwise called as serial interval, was 6.6 days. “We did not observe significantly different viral loads in nasal swabs between symptomatic and asymptomatic,” the authors say in the preprint. Manuscripts posted on preprint servers are yet to be peer-reviewed.

“The transmission potential of COVID-19 is very high and the number of critical cases may become largely unsustainable for the healthcare system in a very short-time horizon,” the authors write. “Aggressive containment strategies are required to control COVID19 spread.”

Progression of disease

If there were just 530 cases on February 28, it increased to 5,830 by March 8. By early March, cases were reported from several areas in Lombardy region, a district of 10 million, which is the epicentre of the epidemic in Italy. As on March 28, there have been 86,498 cases in Italy, which is nearly 5,000 cases more than China’s (81,996), and 9,134 deaths, which is the highest in the world. The authors collected epidemiological data through standardised interviews of confirmed cases and their close contacts. The information gathered included dates of symptom onset, clinical features, respiratory tract specimen results, hospitalisation and contact tracing. The epidemiological analyses were carried out on 5,830 confirmed cases during the period January 14 and March 8.

Immediate response

Contrary to what one might imagine, there has been “almost immediate initial response” by the Regional Health System. The focus was to collect epidemiological data and perform model-based predictions, increase in testing and providing hospital assistance for affected subjects.

The authors say that efforts were taken to limit the spread through contact tracing and isolation. Despite these efforts taken quickly, the number of new cases kept rising steadily leading to “rapid saturation of the health emergency system with a progressive difficulty” in treating COVID-19 patients.

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