Before Memorial Day, the majority of coronavirus cases were found in people 45 and older.
Now, the opposite is true.
People under 45 made up 42% of cases before Memorial Day weekend but 55% of cases reported since then, a new USA TODAY analysis has found.
The trend holds in places where new cases are surging and in those that are not, according to the analysis of data from 25 states and the Centers for Disease Control and Prevention.
The rapid growth in coronavirus infections among younger Americans is one factor behind why some states have broken single-day records this week, and it marks a new phase in a U.S. pandemic that first gained widespread attention with a Washington nursing home outbreak in late February and early March.
Although COVID-19 has been known mainly for its impact on seniors, experts said the disease can debilitate patients in young age cohorts as well. And they warned that an expansion in cases among younger people ultimately threatens any vulnerable person with whom they come in contact.
“Inevitably, infection will spread,” said Stephen Kissler, a postdoctoral researcher and epidemiologist at the Harvard T.H. Chan School of Public Health. “So I think that just because infection is currently mostly spreading in young people is not really a reason to breathe a sigh of relief.”
A shift toward younger patients also has ramifications for school officials making decisions in coming months about reopenings, from K-12 to college.
Total cases among people younger than 45 have grown nearly twice as fast as for people 65 and older since late May, USA TODAY's analysis of CDC data shows. The younger the age cohort, the more rapid the pace of growth. Had all age groups experienced the same, lower growth rate as seniors, the country would have added 30% fewer new cases over the past month.
More:Young Americans less likely to social distance as coronavirus cases continue to rise, survey says
Experts say the shift toward younger patients to some degree reflects a change in testing practices. States that have ramped up their testing capacity are better able to identify people with less severe symptoms, who tend to be younger. Contact tracing is also turning up more children of infected adults.
But in most states, disease trackers say, the data show it’s not just a matter of increased detection. Children, young adults and middle-aged people are being infected more often than before Memorial Day.
One possible reason: They have moved out of lockdown mode more readily than seniors as businesses reopen.
Tyler Workman, 24, recently traveled from Seattle to visit a friend and her friend’s sister in Phoenix, where the group went out together a lot, shopping at Nordstrom and eating at restaurants. Just as the trip ended, Workman learned that her friend’s sister had developed COVID-19.
“For me, in Seattle, you don't even see people walking on the street without their masks on. If they see you on the same sidewalk, they’ll cross the street,” she said. “Being in Arizona, younger people weren’t taking the precautions they should be. Pretty much all the bars were packed.”
Arizona is one of the nation's leading coronavirus hotspots.
Some experts speculate that while older Americans have continued to be cautious about exposure and diligent about precautions like wearing masks, younger age groups have been more likely to return to working and to gathering in person without social distancing.
“We have clearly not reached that population well,” said Dr. Julie Vaishampayan, public health officer for Stanislaus County in California and chairperson of the public health committee of the Infectious Diseases Society of America.
More:Remember Lake of the Ozarks party pics? Many other places boomed Memorial Day
Unlike earlier clusters, which often were linked to particular events or workplaces, Vaishampayan said, an increasing number of cases in her county can’t be tied to a particular place. People – most of them younger – are simply doing more in the community and often without wearing masks or staying 6 feet apart, so there are multiple opportunities to become infected and to infect others.
“It’s making it difficult to control and stop spread because it’s getting overwhelming,” she said.
Workman, the Seattle resident who recently traveled, knew it would be a risk when she left to visit her friend Claudia Ligidakis in Los Angeles. And the 24-year-olds also knew they were heading into a coronavirus hot spot when they drove to Phoenix last Thursday to visit Ligidakis’ family.
Both had been working from home and, for months, had left only to buy groceries or go on a run. Unlike some of their older relatives who believe the coronavirus is a hoax, they have tried to do everything right to stay safe and avoid making others sick.
When they went with Ligidakis’ family to restaurants and shops that Arizona had allowed to open weeks earlier, they wore masks. At Nordstrom, they were surprised to see other customers refuse workers’ requests to put on a face covering.
More:In person, online classes or a mix: Colleges' fall 2020 coronavirus reopening plans, detailed
When Workman, Ligidakis and the sister went to a nighttime DJ event to dance for the first time in ages, they were handed a mask at the door but told, “We have to pass you this, but you don’t have to wear it.”
The three women were among the few who actually did cover their faces.
“It was really awkward,” Workman said.
“You look like such a nerd,” Ligidakis added, chuckling.
Shortly after returning to L.A. on Monday, Ligidakis learned her sister had gone to the hospital and tested positive for the coronavirus. Her mother, too, tested positive. She doesn’t know if they got each other sick or where they became infected. Her father, who usually skips wearing a mask and doesn’t try to social-distance, might’ve picked it up from work in the wine industry and brought it home.
On Wednesday, the two women were working from Ligidakis’ home and waiting for their own test results to come back.
More:See case trends and reopening status state-by-state
Workman can’t understand why some places in the country are acting so much differently than others. After seeing it for herself, Ligidakis is less surprised that cases are growing in Arizona.
“Seattle and L.A. are both pretty hardcore quarantined and Pheonix is really not,” she said. “It was eye-opening how different they really are.”
Link to surges
In addition to national statistics, USA TODAY examined 25 states with published age data available from late May and the past week.
In 18 states with recent increases in new daily case counts, a USA TODAY analysis found that people under 50 comprised 56% to 73% of new infections since late May. Before that, this younger age group accounted for 42% to 65% of all cases.
People under 19 in Arizona accounted for more new cases since Memorial Day than those 65 and older.
“The fact we’re seeing rising numbers along with a higher proportion of tests in some states suggests that, in certain places, it is most likely that there are more infections happening in young people, either through workplace interactions or things opening back up,” said Natalie Dean, a biostatistician specializing in infectious disease epidemiology at the University of Florida.
Even in some states where the coronavirus spread has slowed, total cases are growing faster among people younger than 50 than those who are older.
Indiana is among states where daily new cases have declined in recent weeks. Still, a greater share of their positive test results are coming from younger residents. In the last month, the total number of cases has grown by about 50% for people under age 50, but 30% for people older than that.
More:Study indicates 'virus has slowed its spread' in Indiana
A similar trend can be seen in North Dakota, where new case reports are flat. The total number of North Dakota children through middle-age adults who have been infected grew by 43 percent since late May -- compared with 35 percent for people 50 and older.
Deaths and hospitalizations
Nationally, increasing daily case numbers haven't yet translated to an equally large spike in deaths.
That could be because more cases are among people with less risk for severe symptoms. It might also be because there is a delay between when people test positive and when their cases become acute.
“They may be there weeks or even months before they die,” said Dr. Preeti Malani, chief health officer for the University of Michigan and a professor of infectious diseases. “Even if they survive, they’re left with a lot of debilitating conditions. … A lot of younger people are not hospitalized, but they’re also not working. They’re at home and have prolonged recoveries.”
According to CDC data from 14 states, hospitalizations for people under 50 and older have been declining, but the younger group are a growing share of COVID-19 patients filling beds. The data do not cover some surging states such as Texas, where state records show an increase in hospitalizations. The CDC also notes that its hospital counts are subject to lags in reporting.
Infectious disease experts cautioned it’s only a matter of time before new outbreaks – even among people who are younger – lead to more deaths among Americans of all ages.
In Michigan, cases were generally on a downward trend until an uptick in the past two weeks. Malani celebrated the state’s early success but cautioned the victory is not absolute.
“That gap between being contained and being completely uncontrolled is narrow,” said “It could be a matter of one event or one large gathering. That could be the difference between an entire community being at risk and the spread being contained.”
Growth in Michigan cases since Memorial Day was 20% for people under 50, about double the growth rate for older people.
Dr. Nirav Shah, co-founder of Covid Act Now and a scholar at the Stanford University Clinical Excellence Research Center noted that the number of nursing home deaths was directly correlated to the rate of coronavirus infections in the broader community.
“Individual decisions lead to collective outcomes,” he said.