Younger adults are fueling California’s coronavirus pandemic like never before, health officials are warning, and massive parties and other large social gatherings are threatening to unravel the progress the state is making.

A second surge of COVID-19 cases in Los Angeles County has been fueled by skyrocketing growth in disease transmission and hospitalizations among the youngest adults. Residents under the age of 50 now make up 60% of new coronavirus cases in L.A. County, the county’s public health director, Barbara Ferrer, said.

Young people may feel they are at low risk of becoming seriously ill or dying of the virus. But experts say they can serve as “super spreaders,” easily transmitting the illness to others who are more vulnerable, especially older relatives.

It’s important to ask, Ferrer said, “why so many people are willing to put our entire community at risk during this unprecedented pandemic.”

A number of COVID-19 outbreaks have left younger adults infected in L.A. County. At least 45 people linked to three fraternities associated with the University of Southern California have become infected, as has a group of USC graduate students who have socialized and studied together and some who live together, Ferrer said.

“And at UCLA, we’ve seen a number of football players who returned to campus and tested positive,” Ferrer said.

The University of California, Berkeley in July reported that most of the 47 new cases reported in a single week stemmed from parties connected to fraternities. The outbreak was a factor in the university’s decision to go with fully remote instruction for the fall semester.

Health officials have been particularly dismayed at ongoing reports of large parties happening in the midst of the worst global pandemic in more than a century. An investigation has been launched into a party allegedly thrown for first responders at a Hollywood bar last week, despite a statewide order shutting bars down.

On Monday night, hundreds of people gathered at a mansion on Los Angeles’ Mulholland Drive at a party so big it attracted the attention of television news helicopters. The party, which drew numerous noise complaints before sundown, continued past midnight, when shots rang out, leaving one woman dead and four other people injured.

Concern is also growing that young adults are heading to private homes in tony areas of the city, especially the Hollywood Hills, to party. Los Angeles Mayor Eric Garcetti on Wednesday night authorized shutting off water and electricity service at homes that had repeatedly hosted large parties in defiance of the ban on gatherings.

“While we have already closed all nightclubs and bars, these large house parties have essentially become nightclubs in the hills,” Garcetti said. “These large parties are unsafe and can cost Angelenos their lives.”

Hours after Garcetti’s announcement, police were summoned to the Holmby Hills area after receiving multiple noise complaints in connection with a massive gathering at a mansion. Video showed dozens of people outside, dancing and posing for pictures. Most were not wearing masks.

The crowd, reportedly guests at a large wedding reception, dispersed after police arrived shortly before midnight.

Statewide, Californians ages 18 to 34 make up more than one-third of all infections. In Silicon Valley, coronavirus case rates are increasing particularly fast among people in that age group, said Dr. Sara Cody, Santa Clara County’s health officer.

At Zuckerberg San Francisco General Hospital in early July, the average age of hospitalized COVID-19 patients was 41, said Dr. Grant Colfax.

“The people in the hospital … are not only the elderly and most frail,” Colfax, San Francisco County public health director, said recently. “Young people, middle-aged people, older people — we are all at risk for this disease.”

In L.A. County, new coronavirus cases among adults in their 30s and 40s nearly tripled on July 24 compared with the rate at the beginning of June. At its peak, adults in their 30s and 40s contracted the virus at a daily rate as high as 1,122 cases per 100,000 L.A. County residents in that age group over the previous seven days.

No other age group has a higher case rate.

The youngest adults saw an even faster growth in cases. The rate among those 18 to 29 quadrupled from early June to the end of July, from 200 cases per 100,000 residents to 882, Ferrer said.

“This explosive growth in cases,” she said, “shows that these two age groups continue to drive new infections here in the county, and they’re making up the bulk of our new cases.”

Adults younger than age 50 have similar instances of exposure to the virus at work and while shopping that other groups do. But, compared with other age groups, younger adults socialize with people outside their household at a far greater rate — perhaps spurred by the knowledge that their age group is less likely to die from COVID-19.

“This is also the age group that’s most likely to be attending the large parties that we keep seeing,” Ferrer said. “Gatherings of people from different households are such a bad idea at this point in time.”

Gatherings are banned in L.A. County “because they create a lot of risk for transmission at activities that really are not essential,” she said. Parties and gatherings with people outside of your household “hurt all of us” and, further, make it less likely that children can get back to school anytime soon, allowing more parents to return to work.

“We ask that everyone make good decisions: Don’t host large parties. And don’t attend a party if you’re invited,” Ferrer said. “It isn’t worth the risk you run, and it certainly isn’t worth the risk you’re creating for our collective recovery journey.”

Young adults infected with COVID-19 are also increasingly being hospitalized.

Adults ages 18 to 29 now account for 10% of COVID-19 hospitalizations in L.A. County, double the number in May. Adults in their 30s and 40s account for 1 of every 4 COVID-19 hospitalizations.

Social young adults have also become vectors for the disease in other nations. A study in Japan found that, among 61 clusters of illness, it was most often adults in their 20s or 30s — infected but not showing signs of illness — who were responsible for spreading the infection.

And although it’s still true that the oldest adults are most likely to die from COVID-19, hundreds of younger adults have died from the disease in L.A. County. Among residents in their 30s and 40s, 319 have died, and 32 adults younger than age 30 also have died.

“No matter how young you are,” Ferrer said, “you are at risk for death from COVID-19.”

L.A. County Supervisor Hilda Solis says officials will advertise on billboards and post on Twitter, Facebook and Instagram an educational campaign that targets younger adults and warns that the pandemic is a threat to them. “The risk is real,” Solis said.

Young people can have a false impression that partying only hurts themselves if they get infected, Dr. Anthony Fauci, the U.S. government’s top infectious diseases expert, said at a forum hosted Wednesday by the Harvard T.H. Chan School of Public Health.

What they don’t realize is that, once infected, they likely will become a silent spreader of disease. About 40% of people who get infected show no symptoms but can easily infect others, who can become severely ill and die from COVID-19.

“You are propagating the outbreak,” Fauci said, “which means that you’re going to infect someone, who will infect someone, who then will have a serious consequence.”

Garcetti, too, warned that parties could be venues for so-called super spreader events, in which an outbreak at a large gathering can seed infection in a significant number of people.

If even one significant group fails to do its part to squash the pandemic, all of society is at risk, Fauci said.

“As long as you have any member of society — any demographic group — who is not seriously trying to get to the endgame of suppressing this,” Fauci said, “it will continue to smolder and smolder and smolder. And that will be the reason why, in a non-unified way, we’ve plateaued at an unacceptable level.”


(Times staff writers Leila Miller, Richard Winton and Luke Money contributed to this report.)


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