Super spreader events: how do they cause coronavirus outbreaks and is the White House now a hotspot?

Signs point to the ceremony to nominate Amy Coney Barrett for the Supreme Court on September 26 as a possible source of the coronavirus infections afflicting US President Donald Trump and many members of his inner circle, including wife Melania, former White House counsellor Kellyanne Conway and Trump adviser Chris Christie, former governor of New Jersey.

Though the activity was held outdoors at the Rose Garden, most of the 180-plus people there sat close to each other for an extended period, and most did not wear masks. There were smaller indoor gatherings as part of the occasion. That combination may have resulted in a super spreader event, the type that leads to a cluster of infections.

Others at the ceremony who tested positive for the virus include Republican Senators Mike Lee of Utah and Thom Tillis of North Carolina; John Jenkins, president of Notre Dame University; and a reporter covering the announcement.

Several other persons who have been around the president but did not attend the Rose Garden ceremony also tested positive for the virus last week. They include senior adviser Hope Hicks, Trump campaign manager Bill Stepien and two other journalists who cover the president. White House press secretary Kayleigh McEnany said she has tested positive on Monday morning.

Here’s what you should know about super spreaders:

What is a super spreader event?

There is no precise definition, but generally speaking, it is a gathering that results in a much larger rate of transmission than the norm. As few as 10 to 20 per cent of the carriers may be responsible for up to 80 per cent of new transmissions, according to some studies.

The Centers for Disease Control and Prevention says these events “are associated with both explosive growth early in an outbreak and sustained transmission in later stages”.

The Nebraska Medical Centre lists three “Vs” as common factors in super spreaders:

Venue: Almost always inside, where research indicates transmission is 18 times more likely than outdoors. In the case of the nomination announcement, the indoor gatherings and close conversations at the Rose Garden among attendees without masks might have been the primary culprits.

Ventilation: Lack of circulating fresh air makes it easier for the virus to be inhaled.

Vocalisation: Talking, especially loudly, and singing can aerosolise the virus.

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How do these events happen?

George Rutherford, an infectious disease specialist at the University of California-San Francisco who heads the state’s contact tracing programme, said they are mostly a matter of people being in the wrong place at the wrong time.

“Anyone with Sars-CoV-2 infection is most infectious for a relatively short period of time – like three to four days, starting one day before symptom onset (or roughly four days after exposure),” Rutherford said via email.

“If someone who is in this infectious period comes into close contact with someone who is susceptible, there can be transmission. Super spreading is where someone who is infectious comes into close contact with lots of susceptible people in a relatively short time.”

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What other super spreader events do we know of?

Perhaps the most notorious one was a motorcycle rally August 7-16 in Sturgis, South Dakota, which drew about 462,000 enthusiasts despite warnings from public health experts. There have been conflicting reports about the number of cases that emanated from the rally.

South Dakota officials said in September that 124 state residents tested positive, a figure that does not count those from out of state or whomever they infected. Associated Press reported finding 290 cases nationally from the rally. Regardless, the 10-day activity was a major source of infections.

Other well-known super spreaders include a choir practice in March in Washington state linked to 52 cases, a wedding in August in Maine that led to 170 infections and seven deaths, and a sleepaway camp in June in Georgia tied to at least 260 positive tests. Several outbreaks have been connected to fraternity and sorority parties around college campuses.

How to prevent them?

Since the beginning of the pandemic, public health officials have warned against large gatherings – even at outdoor venues – which is why sporting events, concerts and similar mass activities were cancelled.

Research has shown that even smaller get-togethers such as weddings and barbecues can provoke an outbreak, and experts suggested socialising should be done in limited numbers, outdoors and ideally at a distance and with masks, which are obviously impractical when eating and drinking are involved.

From a public health perspective, the CDC says “prevention and mitigation depends, first and foremost, on quickly recognising and understanding these events. This recognition and understanding enables implementation of control measures specific to the incident and identification of measures, which can reduce the risk for future SSEs.”

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Is the White House now considered a hotspot?

Yes. Even if Hicks and other White House regulars who have been infected are isolated elsewhere, the level of exposure to the virus for other workers is worrisome, and they should quarantine for 14 days.

That is the recommendation of Dr Sunil Sood, infectious diseases specialist at Northwell Health’s South Shore University Hospital in Bay Shore, New York.

“All symptomatic persons should not be present at any workplace location in or outside of the White House,” Sood said, adding that sanitising surfaces does not help much in preventing spread.

“It is being close to others indoor that transmits the virus, which is not 100 per cent eliminated by distancing and masking.”