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Current Affairs

Air borne transmission in public transport

Date: 05 September 2020 Tags: Miscellaneous

Issue

A new study suggests airborne transmission in a bus in China led to one infected individual spreading of COVID-19 to 23 other fellow passengers.

 

Background

The study reports that 128 individuals took two buses on January 19, 2020 on a 100 minute round trip to attend a 150-minute worship event.

 

Details

  • The source patient was a passenger on bus 2 and both the buses had central air conditioners functioning in indoor recirculation mode.

  • On bus 2, 24 individuals turned out to be positive after the event, while none of the individuals in bus 1 were affected. Seven others who turned positive after the outdoor event had all come close to the index patient.

  • The index patient was sitting in the middle seat on the three-seat side of row eight. While those sitting close to the index patient were infected, other cases were spread out across the bus.

  • Significantly, apart from the passenger sitting next to the index patient, none of the passengers sitting in seats close to the bus window developed an infection.

  • The driver and passenger sitting close to the bus door did not develop infection and only one passenger who was sitting close to an openable window developed an infection.

  • The authors say that among the cohort of individuals studied, those that travelled in bus 2 were at a higher risk of contracting the infection than those who did not, implying that the airborne spread of COVID-19 likely contributed to the higher attack rate in the exposed bus.

  • Airborne transmission is defined as the spread of an infectious agent caused by the dissemination of aerosols that remain infectious when suspended in the air over long distances and time.

  • Airborne transmission can happen during aerosol-generating medical procedures and even through speaking and singing.

  • While the high attack rate and the distribution of cases on bus 2 is consistent with airborne transmission, there is no way to rule out a common surface, such as a pole.