On Thursday, the U.S. recorded 40,401 new confirmed cases of COVID-19, easily beating the April 24 one-day record of 36,291. This new surge has taken place in new areas of the country, including states that have resisted stricter measures of containment like Texas and Arizona. And one trend that has set experts’ alarm bells ringing is the growing number of young people affected by the virus.

“What is clear is that the proportion of people who are younger appears to have dramatically changed,” Joseph McCormick, a professor of epidemiology at UTHealth School of Public Health in Brownsville told the New York Times. “It’s really quite disturbing.”

In Arizona, people between 20 and 44 account for half of all cases. In Florida, the average age for someone with a confirmed case is 35 (in March, it was 65). And in Texas, young people actually make up the majority of all cases.

No one is quite sure why the infection rate is seeing an increase among younger people but it’s possible that the restaurants, bars and beaches opening back up have contributed to the rise.

On Thursday, Dr. Robert Redfield, the director of the Centers for Disease Control and Prevention, said that blood test samples suggest the actual number of people with the virus is likely ten times higher than the confirmed number. Young people are more likely to be asymptomatic and less likely to face a lethal case of COVID-19 than older people are, but health professionals are still worried that a surge of young, relatively unaffected people could be spreading the virus to more vulnerable communities. While only 0.6 percent of Americans live in longterm care facilities, they account for 43 percent of all COVID-19 deaths. In Virginia alone, 11 percent of all nursing home and assisted living facility residents have died of COVID-19.

The question is whether this new surge in infections will lead to a similar surge in the death rate. In April, around 2,200 Americans were dying of COVID-19 at the virus’s peak. Now, that number has dropped to about 600 per day, and experts say that the government could move quickly to keep the death rate from climbing.