The number of coronavirus infections in many parts of the United States is more than 10 times higher than the reported rate, according to data released on Friday by the Centers for Disease Control and Prevention.
The analysis is part of a wide-ranging set of surveys started by the C.D.C. to estimate how widely the virus has spread. Similar studies, sponsored by universities, national governments and the World Health Organization, are continuing all over the world.
The C.D.C. study found, for instance, that in South Florida, just under 2 percent of the population had been exposed to the virus as of April 10, but the proportion is likely to be higher now given the surge of infections in the state. The prevalence was highest in New York City at nearly 7 percent as of April 1.
“This study underscores that there are probably a lot of people infected without knowing it, likely because they have mild or asymptomatic infection,” said Dr. Fiona Havers, who led the C.D.C. study. “But those people could still spread it to others.”
She emphasized the importance of hand-washing, wearing cloth masks and social distancing to stop the spread of the virus from people without symptoms.
The numbers indicate that even in areas hit hard by the virus, an overwhelming majority of people have not yet been infected, said Scott Hensley, a viral immunologist at the University of Pennsylvania who was not involved in the research.
“Many of us are sitting ducks who are still susceptible to second waves,” he said.
The difference between recorded infections and the actual prevalence in the data was highest in Missouri, where about 2.65 percent of the population was infected with the virus as of April 26, although many people might not have felt sick. This number is about 24 times the reported rate: nearly 162,000 compared with the 6,800 thought to have been infected by then.
The results confirm what some scientists have warned about for months: that without wider testing, scores of infected people go undetected and circulate the virus.
“Our politicians can say our testing is awesome, but the fact is our testing is inadequate,” Dr. Hensley said. “These are exactly the kind of studies we need right now.”
Dr. Robert Redfield, the director of the C.D.C., hinted at this trend on Thursday during a call with reporters.
“Our best estimate right now is for every case reported there were actually 10 other infections,” Dr. Redfield said.
The source for his claim was unclear at that time. The C.D.C. later posted the data on its website and on MedRxiv, a repository for scientific results that have not yet been vetted by peer review.
The C.D.C. researchers tested samples from 11,933 people across six regions in the United States during discrete periods from March 23 through May 3: The Puget Sound region of Washington where the first Covid-19 case in the country was diagnosed, as well as New York City, South Florida, Missouri, Utah and Connecticut.
[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.]
The samples were collected at commercial laboratories from people who came in for routine screenings, such as cholesterol tests, and were evaluated for the presence of antibodies to the virus — which would indicate previous infection even in the absence of symptoms.
The researchers then estimated the number of infections in each area. New York City, for example, reported 53,803 cases by April 1, but the actual number of infections was 12 times higher, nearly 642,000.
New York City’s prevalence of 6.93 percent in the C.D.C. study is well below the 21 percent estimated by the state’s survey in April. That number was based on people recruited at supermarkets, and so the results would have been biased toward people who would be out shopping during a pandemic — young people, or those who had already had the virus and felt safe, experts said. Dr. Havers also points out that when New York conducted that study, April 19-28, a jump in prevalence would be consistent with the surge of infections in the city at the time.
-
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.
She said the C.D.C. plans to repeat the surveys in all of the regions to see how the prevalence changes over time. Complementary C.D.C. studies will test how well this approach captures the true prevalence.
Saskia Popescu, an epidemiologist at the University of Arizona, said the C.D.C. survey might also be slanted by people with chronic conditions who are more likely to visit commercial labs. Still, it is more representative of the general population than other surveys because it included everyone who came to the labs for a variety of purposes, instead of limiting it to specific groups such as health care workers who felt sick from the coronavirus.
“So much of the serology testing that we’ve been seeing has really been focused on that — people who thought that they were exposed or felt sick at some point,” she said. “This approach is much more representative ultimately.”
She also praised the researchers for not making inferences from the study about the participants’ immune status, because it’s still unclear how the presence of antibodies relates to protection from the virus.
The analysis also highlights the wide disparities between different parts of the country — and the importance not just of enough tests, but also of lab capacity, Dr. Popescu said. In Arizona, she added, the backlog is delaying test results by five to six days.
Dr. Hensley said he was worried that New York and other Northeastern states might falsely believe themselves to be past the point of danger and reopen too soon.
“We need to turn to the South to see what a debacle things have been down there,” he said. “If we open up as Florida or Texas did, you can almost bet that we will be in the same position that they’re in now.”
