Study finds coronavirus superspreader infected more than 20 people on one bus

  • A new study showed how one passenger on a Chinese bus infected 24 others
  • This was early in the outbreak, before mask regulations were implemented
  • For many, public transport cannot be avoided. Wearing a mask can reduce your risk

On 19 January 2020, early in the Covid-19 outbreak, 67 Buddhist passengers and a driver boarded a bus in Ningbo, China, unaware of the risk of getting ill. Since Covid-19 was so new, no-one was wearing a mask.

But days later, 24 people who had been on the bus fell ill. A new study published in JAMA Internal Medicine shows that it took only one person infected with coronavirus to spread the virus to more than a third of the passengers during a trip that took one hour and 40 minutes.

Another case for masks

According to the study, the infected person boarding the bus was not showing any symptoms, but had been in contact with four people from the Hubei province, where the virus had been spreading rapidly.

Hours after the bus ride, the infected person developed a cough, chills, aches and pains – and tested positive for SARS-CoV-2 a few days later. In the meantime, several other passengers had also developed symptoms, and tested positive.

This incident occurred early in the outbreak when the wearing of masks wasn't yet enforced – and demonstrates clearly that the 2m physical distancing rule has little effect in enclosed spaces with restricted ventilation like buses and other modes of public transport.

Renyi Zhang, a professor of atmospheric sciences and chemistry at Texas A&M, and an expert on the impact of aerosols on human health, stated that airborne transmission is an important factor to consider in the spread of the virus and that physical distancing alone is not enough protection against the virus. This once again illustrates the importance of wearing masks in public.

"If the index case had been wearing a mask, that would be the most effective, because that would be source control over the person who's spreading it," said Scott Weisenberg, the medical director of travel medicine at NYU Langone, and an infectious disease physician, after looking at the study.

He states that the study’s results should be treated with caution, and not with panic – as the study isn’t the first to suggest that the virus can spread further than 2m in an enclosed space, and simply reiterates the importance of wearing masks, combined with physical distancing and hand hygiene.

What about planes and other modes of public transport?

With several modes of public transport opening up, including domestic flights in South Africa, we are probably wondering about our risk of infection in these spaces where physical distancing and fresh air are not possible.

A previous study mentioned in a Health24 article, analysed the transmission of coronavirus on a short flight of just under five hours that took place before masks were compulsory. There were seven index cases on the flight, but only two more new transmissions occurred during the flight.

The researchers hypothesised that the cabin's airflow – from ceiling to floor and from front to rear – contributed to the low transmission rate on the plane, and believe that, had masks been worn, the transmission rate would have been even lower. 

Weisenberg also stated that air circulation in buses should always be sufficient, and that the case mentioned above is no cause for alarm.

"People have been crowding onto the free buses [in New York] without a lot of physical distancing for more than two or three months now, and we haven't seen big outbreaks," Weisenberg stated in Science Alert.

How do I lower my risk on public transport?

Although many regulations state that you should only use public transport and fly when absolutely necessary, many people around the world do not have access to cars and rely on buses, trains and taxis to get to work. And international travel is still a necessity in some cases, especially for repatriation, work, study and family reunions.

The best way to reduce your risk of infection (and potentially infecting others while asymptomatic) is to wear a mask for the duration of your trip. The South African Department of Health also states that you should wash your hands before going on public transport; after touching any doors, handrails, window handles or cash; after contact with people; any time before touching your face; and when you arrive at your destination.

READ | Masks could help reduce Covid-19 spread and prevent a second wave 

READ | How to stay safe while flying during the pandemic 

READ | Washing your hands can help curb the spread of coronavirus 

Image credit: Getty Images

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