Sun. Sep 25th, 2022
Crowds of people walk along the Ocean City Boardwalk during Memorial Day weekend on Sunday, May 24, 2020.
enlarge Crowds of people walk along the Ocean City Boardwalk during Memorial Day weekend on Sunday, May 24, 2020.

Much about how the new coronavirus spreads from one victim to another remains a maddening mystery. But amid all the frantic efforts to understand transmission, there’s one finding that seems consistent: that it’s inconsistent.

Some people – most of them even – don’t spread the virus to anyone during their infection. Others infect dozens at once.

It’s a phenomenon that initially resembled deviant anecdotes — a major outbreak of a choral rehearsal in Washington, a South Korean megachurch, a wedding in Jordan — but it has become a regular part of the novel coronavirus, SARS-CoV-2. And researchers have begun to settle for it.

According to mounting data, only 10 to 20 percent of people infected with SARS-CoV-2 are responsible for about 80 percent of transmission. On the other hand, a staggering 70 percent of infected people may not pass the virus on to anyone, some data suggests.

Who will become a so-called super spreader and why is still unknown. Is it something to do with their biology? Something about their infection? Something with their behavior? A combination of those factors? Experts don’t know. But, they claim, we know enough to stop superspreading events — and potentially contain the pandemic.

Superspreading events usually take place in specific environments: large social gatherings, crowded nightclubs, crowded workplaces. Cases where a seemingly highly contagious person can spread it to many others in a short time.

“It’s very difficult to identify an individual superdiffuser,” Barry Bloom, a distinguished professor of public health at Harvard, told Ars. “It’s not difficult to identify events that bring a very large number of people together in a small, enclosed space.”

Benjamin Cowling, a Hong Kong-based epidemiologist and biostatistics expert, agrees. Cowling and colleagues recently studied transmission in Hong Kong, finding that superspreading events caused local transmission. In a recent op-ed, he and a colleague argue that public health policies aimed at stopping the pandemic should focus on stopping superspreading.

“The growth of the epidemic can be controlled with tactics that are much less disruptive socially and economically than the extended lockdowns or other extreme forms of social distancing that much of the world has experienced in recent months,” the researchers wrote.

Cs of transmission

In an email to Ars, Cowling elaborated on this idea a bit, noting that “measures specifically targeting superspreading are measures that reduce or prevent large groups of people,” such as measures to reduce the density of people in schools and workplaces. .

Measures not specifically targeting superspreading, he noted, “are like asking everyone to stay at home as much as possible, despite many workplaces and social environments not being places where superspreading could take place.”

In the op-ed, Cowling noted that Japan — which has been relatively successful in managing the pandemic — has adopted anti-super-dissemination policies, the three Cs: (1) avoid closed spaces with poor ventilation, (2) crowded places, and ( 3) Settings for close contacts, such as close calls. The risk of superspreading is greatest in situations involving all three C’s.

When Cowling and colleagues studied transmission in Hong Kong, which had 1,038 cases at the time, they found that those three Cs seemed to stand out. Superspreading played an inordinate role in local transmission, with large clusters of cases associated with superspreading in bars, weddings and temples. Other clusters linked to work parties, karaoke and dinner parties.

Overall, 539 (52 percent) of all cases in Hong Kong were linked to one of the 135 clusters, while 449 cases were imported sporadically and 50 were sporadic local cases not linked to a cluster. And of the 349 local infections, 196 were linked to just six superspreading events. In one superspreading event, a single person appears to have infected 73 others in a cluster that eventually included 106 cases in bars where a network of musicians played.

Case collection

Overall, the researchers calculated that only 20 percent of cases in Hong Kong accounted for 80 percent of transmission. Another 10 percent of cases spread the infection to just one or two other people, mostly in domestic settings. And the remaining 70 percent of cases did not pass the infection on to anyone.

Surprisingly, only 27 percent ended their quarantined infection when the researchers looked at the people infected during superspreading events, but not infecting anyone else themselves. The authors note that while Hong Kong did not have a strict lockdown or stay-at-home order, residents followed social distancing measures, including restrictions on gatherings.

Cowling and his colleagues’ analysis has been posted online but has not yet been peer-reviewed or published in a scientific journal. But, they note, their findings from Hong Kong are not unique. For example, a study published in April in the Lancet looking at the transmission of SARS-CoV-2 in Shenzhen, China, found that only about 9 percent of cases accounted for 80 percent of the transmission. And a pilot study by researchers in London also found that only about 10 percent of cases can account for 80 percent of transmission.

Superspreading’s large role in outbreaks not only has implications for social distancing measures among the public, it also informs public health officials about how to respond to cases, said William Hanage, an epidemiologist at the Harvard School of Public Health. It shifts the focus from business to transference, he says.

For example, when contact tracers identify a new case, they need to make sure not only do they look forward in time to who that infected person interacted with and potentially get sick, but they also need to look backwards to try and figure out how that new case might be. himself became ill.

“If you determine that transfer has occurred, it means you need to redouble your efforts to test and look around there,” Hanage tells Ars. “Because identifying one transmission means there’s a greater chance that there will be others if you go looking for them.”

By akfire1

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