A study of an Italian town that was among the first in Europe to be hit by coronavirus has highlighted the importance of testing in controlling the disease after it showed that 40 per cent of those who were infected had no symptoms.
Researchers say the study, published in the journal Nature, highlights the important role of people who have no symptoms or are not yet showing symptoms in the spread of the virus.
Researchers from the University of Padua and Imperial College, London carried out their research in the town of Vò in the north of Italy, which was the focus of intense scrutiny after it became one of the first in Europe to lock down as a result of coronavirus.
After the town experienced Italy’s first Covid-19 death on February 21 it was put into immediate quarantine. During this period researchers tested most of the 3,200-strong population - both at the start, when 86 per cent were tested, and two weeks later when 72 per cent of the population was reached.
The testing showed that at the start of the lockdown 73 people (2.6 per cent of the population) were positive for SARS-CoV-2, the virus that causes Covid-19, compared to 29 people (1.2 per cent) two weeks later.
Both times around 40 per cent of the people tested had no symptoms of the disease. None of the children under 10 who were screened tested positive for the disease, despite several living with family members.
All those who tested positive for the virus were quarantined, regardless of whether they showed symptoms, with the town becoming a showcase for the importance of testing.
The virus was suppressed and controlled within a matter of weeks and informed testing policy in the wider Veneto Region, where all contacts of positive cases were offered testing.
“This testing and tracing approach has had a tremendous impact on the course of the epidemic in Veneto compared to other Italian regions, and serves as a model for suppressing transmission and limiting the virus’ substantial public health, economic and societal burden,” said Professor Andrea Crisanti from the Department of Molecular Medicine of the University of Padua.
Researchers also found that asymptomatic people had a similar viral load as symptomatic patients and that pre-symptomatic people (that is those, who have not yet developed symptoms) had a lower viral load at the beginning.
This shows that asymptomatic and pre-symptomatic people have an important role in transmission, the researchers said.
The question over whether asymptomatic people can spread the disease has been the subject of much debate in recent weeks after a World Health Organization expert was forced to clarify her comments after telling a press briefing that there was no evidence of asymptomatic spread.
However, Dr Maria van Kerkhove later said that contact tracing studies showed that there was little evidence of secondary transmission of the disease although modelling pointed to it being responsible for around 40 per cent of spread..
Dr Ilaria Dorigatti, co-lead researcher alongside Prof Crisanti, said the study highlighted the importance of testing as secondary spikes of the disease emerge in cities such as Leicester. "This is particularly relevant today, given the current risk of new infection clusters and of a second wave of transmission,” she said.
Prof Enrico Lavezzo, from the Department of Molecular Medicine of the University of Padua, said the result on asymptomatic carriers is “key”. He said even asymptomatic infections had the potential to contribute to transmission as research from contact tracing in Vò confirmed.
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