According to the World Health Organisation (WHO), community transmission can be defined as the transmission which ‘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, i.e., routine systematic testing of respiratory samples from established laboratories’. It is generally said that community transmission takes place when the source of infection is unknown. One is unable to trace an infection back to a carrier who has travelled in an affected area, or through contact with a person who has the disease.
When a virus circulates in a community, it can infect people with no history. At this stage, it is theoretically possible for everyone to catch the infection either by trend or contact.