The new research comes from the University of Southampton and it weighs up the chances of non-infected commuters catching COVID-19 in a train carriage that is transporting an infectious person.
The study considered high-speed train routes in China, drawing on epidemiological case studies (2,334 infected people and 72,093 travellers in the same cartridge, measured across a three month time period). The key finding was that train passengers sitting within three rows (as assessed width wise) and five columns (as measured lengthwise) from a person infected with SARS-CoV-2 the chance of one of the between commuters contracting the coronavirus infection was between zero and 10.3 percent. The mean rate of transmission under these conditions of ‘close contact’ came out as 0.32 percent.
Within these figures, the data showed that people travelling on the train and sitting directly adjacent to the infected person tended to have the highest level of transmission. This was an average of 3.5 percent of contracting the viral disease. For who sat on the same row as the infected person, the rate was just under half, at 1.5 percent.
The infection rate for any given for each seat, expressed as a dynamic variable by taking the number of people in a given seat diagnosed with COVID-19 and divided by the total number of people who travelled in the same seat on the carriage increased by 0.15 percent for every hour that a person travelled with an infected person patient. Whereas, for those sitting in adjacent seats, the level of increase was significantly higher, standing at 1.3 percent per hour.
However, those who occupied the seat that an infected person sat in only had a low chance of picking up the disease, at just 0.075 percent. This perhaps indicates that the primary risk of contracting the coronavirus comes from airborne droplets rather than the virus being picked up from surfaces.
The research also adds in a temporal aspect in that viral transmission risk is not only a factor of distance relative to an infected person, but also the time that a non-infected person spends in the presence of an infected person. This is borne out in the finding that for the first hour of travel, a safe social distance of greater than one metre is needed to minimize risk. However, after two hours of travelling in close proximity, a distance of less than 2.5 metres should be regarded as insufficient to prevent transmission.
In summary, the data reveals:
1. If an infected person is on a train, and you are in the same carriage, the chance of becoming infected is up to 10%.
2. Those sitting adjacent to the infected person were more likely to become infected compared to those sitting to the side (that is on the same row as the infected person).
3. The risk increased over time and the only way to negate this risk was to move further away. For example, at greater than one metre distance, the risk of infection over the course of one hour was lower than any time after one hour had elapsed. Once an hour had elapsed the same person would need to be sitting 2.5 metres away to lower their chances of infection back to the level within the first hour.
4. Sitting in the same seat that an infected person had sat in proved to be very low (0.07%), indicating that the risk of picking up viruses from the surfaces was much lower than being in close proximity to a person breathing.
Such findings may be applicable to an office environment as well. What is interesting is that distance is something that changes dynamically, in that the greater the time spent close to an infected person the further away you need to be as time passes.
The research study has been published in the journal Clinical Infectious Diseases. The paper is titled “The risk of COVID-19 transmission in train passengers: an epidemiological and modelling study.”