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According to the World Health Organization (WHO), community transmission “is evidenced by the inability to relate confirmed cases through chains of transmission for a large number of cases, or by increasing positive tests through sentinel samples (routine systematic testing of respiratory samples from established laboratories)”.
In other words, a community transmission case is generally accepted as referring to an infected patient without any known contact with another confirmed case of viral infection or recent travel history to or from a country badly affected by a pandemic. Therefore, the community transmission of a virus essentially implies that a virus is moving freely in the community.
A state of community spread implies that the virus is now circulating in the community, and can infect people with no history of travel to or contact with affected people and areas. At this stage, it is theoretically possible for everyone in a community or country to catch the infection.
Community transmission explained
In the context of coronavirus, if a person is diagnosed with Covid-19, their infection is either linked to travel history to a country where the disease is widespread, or if that person has come in contact with someone already infected.
When the source of transmission for a large number of people is not traceable, it is called a community transmission.
Why is community transmission worrisome?
This is particularly worrisome for health officials because that means the virus is in the community but no one knows where it has come from or can track its origins. This also suggests the virus is widespread in a community.
Have there been cases of community transmission in the world?
Cases of community transmission of Covid-19 have been confirmed in the US, UK, Australia and Indonesia.
Coronavirus in India: Has the country reached community transmission stage?
The government has so far maintained that there is no community transmission in India. Some experts, however, disagree. Delhi Health Minister Satyendar Jain on June 9, 2020, said the source of Covid-19 infection in 50 per cent of the cases in the national capital was unknown. It was, however, up to the Centre to declare whether the city had entered the community transmission phase, he added.
The Delhi health minister also indicated that the assessment of the local administration pointed towards the “third stage of spread”. “Director AIIMS Randeep Guleria said (there had been community transmission) but Centre has not yet confirmed it,” Jain said.
Are we infecting one another?
In the context of coronavirus, medical experts say the virus is indigenously spreading — at first it was an outbreak imported from outside, then it became an Indian epidemic and today this is what it is," said Dr Jacob John, a prominent virologist.
"We are infecting each other. That is the true definition of community transmission. The source is now immaterial. It is truly an indigenous epidemic. It is spreading in the community, so, according to my definition, there is community transmission.
Cases of community transmission in other diseases
Most types of influenza and bird flu outbreaks in the past were known to have spread through community transmission. The H1N1 outbreak of 2009, commonly known as swine flu, primarily spread through community transmission.