Public enclosed spaces like workplaces and restaurants can become super-spreading environments for Covid-19; however, schools are not prominent transmission centres; children are unlikely to be the source of any household infection.
These common findings of 14 studies on transmission patterns across nine countries could provide some pointers as the Centre and state governments work on exit strategies ahead of May 17, when the third phase of the nationwide lockdown is scheduled to end.
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The studies tracked index patients and the channels of contagion (home, public transport, workplaces, religious gatherings) in China, Iran, South Korea, Singapore, Iceland, France, Taiwan, Japan and the US.
Stating that enclosed public gatherings and mass living spaces are high-risk environments, they highlighted the importance of ventilated, open spaces.
While some studies found that household contacts account for 10-20 per cent of the transmission, 5-10 per cent was traced to transportation, dining and entertainment.
A window to future
As countries around the world prepare for a reopening of their economies and a gradual return to normal life, studies by global researchers on transmission patterns of the disease provide a glimpse into the new post-COVID world — especially how hospitality, entertainment, airlines, and shopping could change.
“Our findings suggest that COVID-19 is largely transmitted by close contact, particularly when contact occurs over a prolonged period and in close congregation,” said a study in The Lancet.
It cited a case study in Singapore, where a church gathering was responsible for more than half of an index patient’s positive secondary contacts, while another 23 per cent of the positive contacts were from a family gathering.
“Risk of transmission could be reduced if symptomatic people do not attend events in which prolonged social interactions take place,” it said.
Similarly, in Boston, 147 out of 408 (36 per cent) residents in a homeless shelter tested positive. In China, 57 of 89 (64 per cent) residents of a nursing facility tested positive.
The population density of a city played a major role in China, according to American and European researchers in a paper on medRxiv (a portal for papers that are yet to be peer-reviewed).
“Here we show that the epidemic intensity of COVID-19 is strongly shaped by crowding,” said the study, adding that the pandemic in China was spread across a wide range of geographic contexts. The population size, mean temperature, and mean humidity were found to be smaller influencers than density.
In another common thread, the studies found that schools were not prominent transmission centres, especially for children below 10 years of age. Children were also not found to be the source of household infection for adults.
According to an Oxford study, the index patient – an Englishman returning from Singapore – resided for four days in a chalet in the French Alps. Nine out of 11 tourists in his apartment, and three out of five in an adjacent apartment tested positive.
After the index patient left, five new tourists stayed in the main apartment with some of his secondary contacts – one of the five tested positive.
However, one of the positive secondary contacts was a child, who had visited three different schools and made contact with a large number of people. None of the contacts was infected.
“The fact that an infected child did not transmit the disease despite close interactions within schools suggests potential different transmission dynamics in children,” said the study.
An Australian study, in medRxiv, also found that children are unlikely to be the source of any household infection, in sharp contrast to the bird flu where 54 per cent of transmission clusters identified children as the source of infection.
In Iceland, a population screening of thousands of people found that no child under 10 years was positive.
Nonetheless, household transmission for COVID-19 is particularly high, even more than SARS and MERS, according to another study in medRxiv which is based on Guangzhou.
But an Oxford-published research from across China found that those who quarantined themselves in their own households did not transmit the disease to any other member, suggesting that home quarantine can be possible if proper isolation protocol is followed.
There were, however, some differences in the studies. While a study of cases in Taiwan, published in The Journal of American Medical Association, found household transmission to be the main source of infection, The Lancet study of the US found that healthcare transmission was more than household transmission.
Some of the papers were summary findings of patterns in a bulk of other articles.
Speaking at the Express e-Adda on Monday, AIIMS Director Dr Randeep Guleria, who is part of the core team of top officials reviewing and monitoring the pandemic in the country had said India’s population density remains a concern.
Talking about public spaces post-lockdown, he said: “There will be huge effects on various industries – hospitality, entertainment, airlines, shopping malls. How do we travel with social distance? Do we leave some seats empty? How do we sit in buses and trains? We need a different strategy for metros. There has to be micro-planning.”