Coronavirus: Are super spreaders behind the rise in the number of cases?

Arguably the most famous is known as Typhoid Mary

Passengers talk to each other on the balconies of their cabins on the cruise ship Diamond Princess, where dozens of passengers were tested positive for coronavirus, at Daikoku Pier Cruise Terminal in Yokohama, south of Tokyo, Japan, February 11, 2020. REUTERS/Issei Kato

About three weeks ago, a British businessman travelled to Singapore for a conference. While he was there, he was infected with the coronavirus.

Unaware he was a carrier, he stopped off to see family members who were staying in a ski chalet in France, where he infected at least 11 people.

Studies suggest that on an average, each person infected with the new coronavirus passes it on to two or three people.

But in this case the businessman infected many people, making him a super spreader.

Scientists say super spreaders can infect several people during outbreaks, sometimes many times, making it difficult to contain a disease.

But how does that happen? How can one person pass on more pathogens than others?

The National explains.

Are super spreaders new?

No. Super spreaders can be traced to outbreaks more than 100 years ago.

Possibly the most famous was a woman called Mary Mallon, who came to be known as Typhoid Mary.

Mallon worked as a cook for several wealthy New York families throughout her career in the 20th century.

As an asymptomatic carrier of typhoid fever, she infected 51 people.

A typhoid researcher identified Mallon as a super spreader who infected everyone around her.

Super spreaders cause the outbreak to spread faster. They are the catalysts for epidemics

She was forcibly isolated twice and spent about 30 years in quarantine after being declared a super spreader.

There were super spreaders during the outbreaks of Sars and Mers, which are close cousins of the new coronavirus.

During the 2015 outbreak of Mers in South Korea, one patient infected 85 people.

How does one become a super spreader?

There are several theories. Scientists believe a person’s potential to become a super spreader is controlled by their immune system and behaviour.

In the case of the British super spreader, his immune system was strong. He was shedding the virus but showed no symptoms.

Most people are not super spreaders. Scientists believe 20 per cent of patients infect more people than the average infected person.

Dr Somansu Basu, a microbiologist and chairman of infection control at NMC Speciality Hospital in Al Ain, said super spreaders are one of two types of people.

They have either exceptionally strong or very weak immune systems.

“Scientists believe these people either have a low immune system, so they have a high viral load, or they have a very strong immune system so they don’t develop the symptoms and go about their daily lives, but continue shedding the virus in the environment and to other people,” Dr Basu said.

Can we identify suspects?

We do not know. It is only after an outbreak dies out that studies are conducted to identify the super spreaders such as Typhoid Mary and the South Korean patient.

Are there super spreaders in every outbreak?

No. Not all virus outbreaks will have super spreaders but some can provide data and trends to scientists and researchers.

“If the virus has epidemic potential, there are super spreaders,” Dr Basu said. “We saw it in Sars. We saw it in Mers. We saw it in Ebola. We have seen it influenza.

"And we have now seen it in this novel coronavirus. But there are so many other viruses. Super spreaders cause the outbreak to spread faster. They are the catalysts for epidemics."

Has a super spreader infected people on board the 'Diamond Princess' ship?

There are fears of an epidemic on board the Diamond Princess off Yokohama in Japan. One known case has mushroomed to 135.

Dr Basu said it was likely that there were one or even two super spreaders on the ship. That would help to explain the sharp increase in the number of cases.

“This exponential rise in the number of cases is not possible unless some super-spreading transmission is happening," he said.

How worried should we be?

“It is important that the role of super spreaders is not overstated,” said Dr Ahmad Nusair, a staff physician who specialises in infectious diseases at Cleveland Clinic Abu Dhabi.

They exist, as they have in previous viral outbreaks. They were eventually reined in using effective infection control measures.

Dr Nusair said being vigilant was key in preventing the spread of the virus. That means avoiding areas where the virus is spreading, washing your hands frequently, and so on.

“These precautions will be still protective even around super spreaders,” he said.