Why You May Not Be Spreading Coronavirus

loading...

At a May 30 birthday party in Texas, one man reportedly infected 18 friends and family with the coronavirus.

Reading reports like these, you might think of the virus as a wildfire, instantly setting off epidemics wherever it goes. But other reports tell another story altogether.

In Italy, for example, scientists looked at stored samples of wastewater for the earliest trace of the virus. Last week they reported that the virus was in Turin and Milan as early as Dec. 18. But two months would pass before northern Italy’s hospitals began filling with victims of Covid-19. So those December viruses seem to have petered out.

As strange as it may seem, these reports don’t contradict each other. Most infected people don’t pass on the coronavirus to someone else. But a small number pass it on to many others in so-called superspreading events.

“You can think about throwing a match at kindling,” said Ben Althouse, principal research scientist at the Institute for Disease Modeling in Bellevue, Wash. “You throw one match, it may not light the kindling. You throw another match, it may not light the kindling. But then one match hits in the right spot, and all of a sudden the fire goes up.”

Understanding why some matches start fires while many do not will be crucial to curbing the pandemic, scientists say. “Otherwise, you’re in the position where you’re always one step behind the virus,” said Adam Kucharski, an epidemiologist at the London School of Hygiene and Tropical Medicine.

When the virus first emerged in China, epidemiologists scrambled to understand how it spread from person to person. One of their first tasks was to estimate the average number of people each sick person infected, or what epidemiologists call the reproductive number.

The new coronavirus turned out to have a reproductive number somewhere between two and three. It’s impossible to pin down an exact figure, since people’s behavior can make it easier or harder for the virus to spread. By going into lockdown, for instance, Massachusetts drove its reproductive number down from 2.2 at the beginning of March to 1 by the end of the month; it’s now at .74.

This averaged figure can also be misleading because it masks the variability of spread from one person to the next. If nine out of 10 people don’t pass on a virus at all, while the 10th passes it to 20 people, the average would still be two.

In some diseases, such as influenza and smallpox, a large fraction of infected people pass on the pathogen to a few more. These diseases tend to grow steadily and slowly. “Flu can really plod along,” said Kristin Nelson, an associate professor at Emory University.

But other diseases, like measles and SARS, are prone to sudden flares, with only a few infected people spreading the disease.

Epidemiologists capture the difference between the flare-ups and the plodding with something known as the dispersion parameter. It is a measure of how much variation there is from person to person in transmitting a pathogen.

But James Lloyd-Smith, a U.C.L.A. disease ecologist who developed the dispersion parameter 15 years ago, cautioned that just because scientists can measure it doesn’t mean they understand why some diseases have more superspreading than others. “We just understand the bits of it,” he said.

When Covid-19 broke out, Dr. Kucharski and his colleagues tried to calculate that number by comparing cases in different countries.

If Covid-19 was like the flu, you’d expect the outbreaks in different places to be mostly the same size. But Dr. Kucharski and his colleagues found a wide variation. The best way to explain this pattern, they found, was that 10 percent of infected people were responsible for 80 percent of new infections. Which meant that most people passed on the virus to few, if any, others.

Dr. Kucharski and his colleagues published their study in April as a preprint, a report that has not been reviewed by other scientists and published in a scientific journal. Other epidemiologists have calculated the dispersion parameter with other methods, ending up with similar estimates.

In Georgia, for example, Dr. Nelson and her colleagues analyzed over 9,500 Covid-19 cases from March to May. They created a model for the spread of the virus through five counties and estimated how many people each person infected.

In a preprint published last week, the researchers found many superspreading events. Just 2 percent of people were responsible for 20 percent of transmissions.

Now researchers are trying to figure out why so few people spread the virus to so many. They’re trying to answer three questions: Who are the superspreaders? When does superspreading take place? And where?

As for the first question, doctors have observed that viruses can multiply to bigger numbers inside some people than others. It’s possible that some people become virus chimneys, blasting out clouds of pathogens with each breath.

Some people also have more opportunity to get sick, and to then make other people sick. A bus driver or a nursing home worker may sit at a hub in the social network, while most people are less likely to come into contact with others — especially in a lockdown.

  • Updated June 24, 2020

    • Is it harder to exercise while wearing a mask?

      A commentary published this month on the website of the British Journal of Sports Medicine points out that covering your face during exercise “comes with issues of potential breathing restriction and discomfort” and requires “balancing benefits versus possible adverse events.” Masks do alter exercise, says Cedric X. Bryant, the president and chief science officer of the American Council on Exercise, a nonprofit organization that funds exercise research and certifies fitness professionals. “In my personal experience,” he says, “heart rates are higher at the same relative intensity when you wear a mask.” Some people also could experience lightheadedness during familiar workouts while masked, says Len Kravitz, a professor of exercise science at the University of New Mexico.

    • I’ve heard about a treatment called dexamethasone. Does it work?

      The steroid, dexamethasone, is the first treatment shown to reduce mortality in severely ill patients, according to scientists in Britain. The drug appears to reduce inflammation caused by the immune system, protecting the tissues. In the study, dexamethasone reduced deaths of patients on ventilators by one-third, and deaths of patients on oxygen by one-fifth.

    • What is pandemic paid leave?

      The coronavirus emergency relief package gives many American workers paid leave if they need to take time off because of the virus. It gives qualified workers two weeks of paid sick leave if they are ill, quarantined or seeking diagnosis or preventive care for coronavirus, or if they are caring for sick family members. It gives 12 weeks of paid leave to people caring for children whose schools are closed or whose child care provider is unavailable because of the coronavirus. It is the first time the United States has had widespread federally mandated paid leave, and includes people who don’t typically get such benefits, like part-time and gig economy workers. But the measure excludes at least half of private-sector workers, including those at the country’s largest employers, and gives small employers significant leeway to deny leave.

    • Does asymptomatic transmission of Covid-19 happen?

      So far, the evidence seems to show it does. A widely cited paper published in April suggests that people are most infectious about two days before the onset of coronavirus symptoms and estimated that 44 percent of new infections were a result of transmission from people who were not yet showing symptoms. Recently, a top expert at the World Health Organization stated that transmission of the coronavirus by people who did not have symptoms was “very rare,” but she later walked back that statement.

    • What’s the risk of catching coronavirus from a surface?

      Touching contaminated objects and then infecting ourselves with the germs is not typically how the virus spreads. But it can happen. A number of studies of flu, rhinovirus, coronavirus and other microbes have shown that respiratory illnesses, including the new coronavirus, can spread by touching contaminated surfaces, particularly in places like day care centers, offices and hospitals. But a long chain of events has to happen for the disease to spread that way. The best way to protect yourself from coronavirus — whether it’s surface transmission or close human contact — is still social distancing, washing your hands, not touching your face and wearing masks.

    • How does blood type influence coronavirus?

      A study by European scientists is the first to document a strong statistical link between genetic variations and Covid-19, the illness caused by the coronavirus. Having Type A blood was linked to a 50 percent increase in the likelihood that a patient would need to get oxygen or to go on a ventilator, according to the new study.

    • How many people have lost their jobs due to coronavirus in the U.S.?

      The unemployment rate fell to 13.3 percent in May, the Labor Department said on June 5, an unexpected improvement in the nation’s job market as hiring rebounded faster than economists expected. Economists had forecast the unemployment rate to increase to as much as 20 percent, after it hit 14.7 percent in April, which was the highest since the government began keeping official statistics after World War II. But the unemployment rate dipped instead, with employers adding 2.5 million jobs, after more than 20 million jobs were lost in April.

    • What are the symptoms of coronavirus?

      Common symptoms include fever, a dry cough, fatigue and difficulty breathing or shortness of breath. Some of these symptoms overlap with those of the flu, making detection difficult, but runny noses and stuffy sinuses are less common. The C.D.C. has also added chills, muscle pain, sore throat, headache and a new loss of the sense of taste or smell as symptoms to look out for. Most people fall ill five to seven days after exposure, but symptoms may appear in as few as two days or as many as 14 days.

    • How can I protect myself while flying?

      If air travel is unavoidable, there are some steps you can take to protect yourself. Most important: Wash your hands often, and stop touching your face. If possible, choose a window seat. A study from Emory University found that during flu season, the safest place to sit on a plane is by a window, as people sitting in window seats had less contact with potentially sick people. Disinfect hard surfaces. When you get to your seat and your hands are clean, use disinfecting wipes to clean the hard surfaces at your seat like the head and arm rest, the seatbelt buckle, the remote, screen, seat back pocket and the tray table. If the seat is hard and nonporous or leather or pleather, you can wipe that down, too. (Using wipes on upholstered seats could lead to a wet seat and spreading of germs rather than killing them.)

    • What should I do if I feel sick?

      If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor. They should give you advice on whether you should be tested, how to get tested, and how to seek medical treatment without potentially infecting or exposing others.


Dr. Nelson suspects the biological differences between people are less significant. “I think the circumstances are a lot more important,” she said. Dr. Lloyd-Smith agreed. “I think it’s more centered on the events.”

A lot of transmission seems to happen in a narrow window of time starting a couple days after infection, even before symptoms emerge. If people aren’t around a lot of people during that window, they can’t pass it along.

And certain places seem to lend themselves to superspreading. A busy bar, for example, is full of people talking loudly. Any one of them could spew out viruses without ever coughing. And without good ventilation, the viruses can linger in the air for hours.

A study from Japan this month found clusters of coronavirus cases in health care facilities, nursing homes, day care centers, restaurants, bars, workplaces, and musical events such as live concerts and karaoke parties.

This pattern of superspreading could explain the puzzling lag in Italy between the arrival of the virus and the rise of the epidemic. And geneticists have found a similar lag in other countries: The first viruses to crop up in a given region don’t give rise to the epidemics that come weeks later.

Many countries and states have fought outbreaks with lockdowns, which have managed to draw down Covid-19’s reproductive number. But as governments move toward reopening, they shouldn’t get complacent and forget the virus’s potential for superspreading.

“You can really go from thinking you’ve got things under control to having an out-of-control outbreak in a matter of a week,” Dr. Lloyd-Smith said.

Singapore’s health authorities earned praise early on for holding down the epidemic by carefully tracing cases of Covid-19. But they didn’t appreciate that huge dormitories where migrant workers lived were prime spots for superspreading events. Now they are wrestling with a resurgence of the virus.

On the other hand, knowing that Covid-19 is a superspreading pandemic could be a good thing. “It bodes well for control,” Dr. Nelson said.

Since most transmission happens only in a small number of similar situations, it may be possible to come up with smart strategies to stop them from happening. It may be possible to avoid crippling, across-the-board lockdowns by targeting the superspreading events.

“By curbing the activities in quite a small proportion of our life, we could actually reduce most of the risk,” said Dr. Kucharski.

loading...


Source link
(Visited 1 times, 1 visits today)

Related posts:

Brexit talks resume in London after tough week in Brussels
France's new Prime Minister Jean Castex to unveil reshuffled cabinet
Australia closes state border for first time in 100 years to stop spread of Covid-19
Desperate search for survivors as dozens feared dead in southwest Japan floods
New guidelines for children and adolescents with type 2 diabetes
Croatia's ruling conservatives win parliamentary vote
UK pays tribute to National Health Service on 72nd birthday
Assessing the Real Coronavirus Death Rate: Live Updates
Kazakhstan imposes 'second wave' of restrictions as coronavirus surges
239 Experts With One Big Claim: The Coronavirus Is Airborne
Fresh Spanish virus outbreak sees 70,000 locked down
Greece shuts border to Serbians after virus spike
India reports record daily cases in coronavirus battle
Formula One drivers all wear ‘End Racism’ T-shirts at season-opening Austrian Grand Prix
South Africa deploys military medics to virus hotspot
Algeria buries repatriated skulls of resistance fighters as it marks independence from France
How Covid-19 contaminated French tourism
Iran reports its highest one-day Covid-19 death toll, topping record set earlier in week
Iran reports new record one-day virus death toll of 163: official
Death toll in Ethiopia surpasses 150 from demonstrations following killing of popular singer
Mexico's COVID deaths pass 30,000, world's 5th highest total
Virus spike in Spain reveals plight of seasonal farm workers
Japan flooding leaves dozens dead and missing
US records 43,742 new virus cases in 24 hours: tracker
S.Africa reports 10,000 new infections in record 24-hour surge
Green, left-wing Michèle Rubirola becomes Marseille’s first woman mayor
Italy could transfer migrants from Ocean Viking rescue ship on Monday
Mexico Covid-19 deaths exceed 30,000, making it fifth-hardest hit country
US marks polarized July 4 as Trump vows to defeat ‘radical left’ protesters
DNA Linked to Covid-19 Was Inherited From Neanderthals, Study Finds
Coronavirus Updates: Trump Hosts July 4 Event at White House
239 Experts With 1 Big Claim: The Coronavirus Is Airborne
Thousands march in Paris for LGBT rights
How Infrared Images Could Be Part of Your Daily Life
EXCLUSIVE: Algerian President Tebboune says opportunity exists for "appeased relations" with France
Why some people don't want to take a COVID-19 test
Beijing lifts most travel restrictions, says city's outbreak contained
Novel method proposed on multiparametric-MRI for rectal cancer diagnosis
Moderate Drinking May Be Good for the Brain
Russia announces virus deaths exceed 10,000
Hong Kong libraries pull books by territory’s pro-democracy activists in wake of China security law
The Pandemic’s Big Mystery: How Deadly Is the Coronavirus?
Mexico reverses some openings as virus cases continue high
Area C, the chunk of the West Bank the Israeli right has long coveted
Dog in Georgia tests positive for virus that causes COVID-19
Pubs open, gyms shut: England's health dilemma
China plans reforms to organ donation rules
Covid 19: Making the poor poorer
Catalonia places 200,000 people under new lockdown following Covid-19 surge
US marks record 57,683 new COVID-19 cases in 24 hours: tracker
As much of US marks a muted Independence Day, Trump encourages big parties
WHO says first alerted to virus by its office, not China
Paris's Louvre reopens on Monday after lockdown losses of 'over €40 million'
How coronavirus self-isolation fatigue may lead to more beach drownings this summer
what's the new coronavirus saliva test, and how does it work?
The WHO's risky communication strategy created confusion around COVID-19
England's pubs, restaurants and hairdressers reopen as COVID-19 lockdown eases
French jihadist sentenced to 30 years for IS group executions in Syria
We looked at the health star rating of 20,000 foods and this is what we found
Trump rallies against anti-racism protesters seeking to 'defame' heroes
The US has bought most of the world's remdesivir. Here's what it means for the rest of us
Antibodies against phosphorylcholine give protection against rheumatic systemic disease
Researchers determine how much oxygen the brain needs
Britain eases virus quarantine as US under siege
Researchers find fans of apocalyptic movies may be coping with pandemic better
Some say allow family access to dying patients with COVID-19
11 of Our Best Weekend Reads
China aims to phase out sale of live poultry at food markets
U.S. Coronavirus Cases Are Rising Sharply, but Deaths Are Still Down
Spain counts 17 new virus deaths in 24 hours
At least thirty villagers massacred in central Mali terror attacks
Point-prevalence surveys in SNFs help cut COVID-19 transmission
Saudi Arabia passes 200,000 virus cases
French court opens inquiry into former PM Philippe in handling of Covid crisis
Protective antibodies identified for rare, polio-like disease in children
Air France to cut 7,580 jobs at French flagship carrier and regional unit Hop!
New French PM Castex says priority to meet Covid-19 pandemic, economic crisis as he takes helm
'Data not lying', WHO urges countries to 'wake up' and halt virus
Prosecutors seek life term for French jihadist accused of Syria executions
Mystery of hundreds of elephants found dead in Botswana
Injuries shoot up after fireworks laws loosened in West Virginia
‘We can’t afford an ounce of meat’: Economic crisis strangles Lebanon
Algeria welcomes remains of fighters against colonisation from France
Neurological symptoms described in children with COVID-19
United States: In Louisiana, Cajuns are keen to preserve their identity
HIV may not worsen COVID-19 outlook
250. Split-Lebertransplantation am UKR - Biermann Medizin
Live Coronavirus Updates: U.S. Leaders Change Course
EU authorises use of remdesivir to treat coronavirus
Turkey challenges allies and enemies alike in quest for ‘larger role on world stage’
Porres neuer Chefarzt in Leverkusen
Even gut immune response is site-specific
Systemische Therapie kann jetzt mit den Krankenkassen abgerechnet werden
Inflammatory Bowel Disease Tied to Increased Dementia Risk
Macron names Jean Castex as new French prime minister
Popular chemotherapy drug may be less effective in overweight and obese women
Studie: Junge Menschen rauchen und trinken weniger
Can an Algorithm Predict the Pandemic’s Next Moves?
Death toll climbs to more than 160 in Myanmar jade mine disaster
Israeli, UAE technology firms pen deal on virus research

Leave a Reply

Your email address will not be published. Required fields are marked *

Next Post

Maqedoni: Katër viktima dhe 126 raste të reja me koronavirus për 24 orë

Tue Jun 30 , 2020
Gjatë 24 orëve të fundit katër persona kanë ndërruar jetë si pasojë e koronavirusit, kurse nga 1140 testimeve të realizuara, 126 kanë rezultuar pozitive. Sipas qyteteve: Shkup-66, Kumanovë-6, Shtip-15, Prilep-3, Tetovë-19, Strugë-2, Veles-2, Manastir-1, Kavadar-4, Gostivar-2, Probishtip-2, Shën Nikollë-1, Resnje -3. Instituti i Shëndetit Publik në Maqedoni ka regjistruar 48 […]
Afro 14 mijë raste të reja me koronavirus në Brazil