The symptoms arrived, one after the next, for more than two weeks.

Exhaustion, coughing, fever, body aches — as one passed, another took its place.

“I’m definitely someone who suffers from a little bit of extra anxiety to begin with,” said Lauren Tomaszewski, who tested positive for COVID-19 in April. “There was a lot of constant checking my vital signs to reassure myself I didn’t have to go to the hospital, that I would be OK.”

After the virus had cleared her system, it took weeks for the 29-year-old physical therapist and daily runner to regain her strength.

“I’m young and healthy, and it knocked me on my butt. I don’t wish it on anyone,” she said. “The emotional toll it took getting healthy and rehabbing I also don’t wish on anyone.”

In recent weeks, COVID-19′s rise among younger people has become a national phenomenon, and is particularly dramatic in states where the virus is surging, including Texas, California and Florida.

To a lesser extent, the same trends are appearing in Pennsylvania and New Jersey, even as the states have fought to lower infection rates.

In April, people ages 18 to 29 made up 12% of New Jersey’s total COVID-19-positive test results. Now, that’s up to 22%. Pennsylvania analyzes its demographic data differently, with people ages 25 to 49 grouped in one category, but people ages 19 to 24 accounted for 5.9% of all cases at the beginning of May, and their share of overall positive cases has crept up to 6.6% as of this week. Positive test results among children and teenagers rose 2 percentage points, to 4.5% of all cases, from May to the end of June.

» READ MORE: Coronavirus cases trend downward around Philadelphia, but masks are here to stay

The number of children and teenagers testing positive in Philadelphia concerns city health officials. There were 99 positive test results among those 16 to 19 the week of June 14, city data showed, more than double what was reported the week of May 24. The increase likely stems from graduation parties and beach house stays, said Thomas Farley, the city’s health commissioner.

“We’re definitely concerned about it,” Farley said. “Teenagers are getting it, and they’re inevitably going to spread it to some of their parents.”

The widespread protests over police brutality appear to not be a factor in the increase, Farley said, explaining that such a spike would have shown up earlier.

» HELP US REPORT: Are you a health care worker, medical provider, government worker, patient, frontline worker or other expert? We want to hear from you.

The increase in cases among teens and young adults is partly a result of more widely available testing, said Amesh A. Adalja, an epidemiologist at Johns Hopkins University’s Center for Health Security. Younger people are less likely to get seriously ill from the coronavirus, and initially testing was reserved for those with severe symptoms.

But eagerness to get out of isolation is probably a bigger factor, he said. Reopened bars and restaurants are proving irresistible to younger people.

“As stay-at-home orders are lifted, you find that younger people tend to be more risk-tolerant,” Adalja said.

Tomaszewski, who thinks she may have caught the virus from one of her physical therapy patients, took the virus seriously when it emerged, she said. She wore masks. Even before she got sick, she decided to move out of the South Philadelphia apartment she shared with her husband to her mother’s home in Yardley, where there was space for her to socially distance. The couple’s lease on their South Philadelphia apartment has since expired and her husband has also moved to Yardley.

Even with those precautions, she noticed signs of trouble one day while running.

“Amid a three-mile run, I had to stop and walk three times, which is a little weird,” said the former marathoner.

Within days, she had to stop to catch her breath while walking up stairs. She tested her oxygen level with an oximeter and found it was 80%, a dangerously low level, though it quickly rose again with deep breaths. Then she developed a fever. Chest pains so acute she couldn’t draw a deep breath followed, she said, “which added to the cycle of feeling like you couldn’t get oxygen in.” Body aches followed, wracking her legs and lower back.

Because she was so careful to isolate, she believes she did not transmit the virus to anyone. She consulted with doctors remotely, but never had to go to a hospital.

» READ MORE: Should I wear a mask while running and exercising outside?

As the pandemic wears on, officials said, they aren’t seeing younger people taking that kind of care.

“We are especially concerned after gatherings we saw over the weekend at the Jersey Shore and another bar in Northern New Jersey,” Judith Persichilli, the state’s health commissioner, said in a news briefing this week.Individuals were packed together at these locations, which raises the risk of spreading COVID-19 to one another, and then on to a wider community.”

She noted that 640 New Jersey residents ages 18 to 29 have been hospitalized with COVID-19, and 15 have died. Pennsylvania reported six deaths among 25- to 29-year-olds during the pandemic.

Unlike many other places in the country, Pennsylvania and New Jersey are not experiencing dramatic surges in cases. Pennsylvania’s count of new daily COVID cases has begun to swing upward in recent days, though. New Jersey’s counts have remained flat. South Jersey and Philadelphia, though, both reported a recent increase in new daily cases Friday.

Whether the rise of cases among young people will lead to a spike in deaths remains uncertain. Younger people are at very low risk of dying or being hospitalized from COVID-19. Less than 4% of all COVID-positive people aged 20 to 29 have required hospitalization, the Centers for Disease Control and Prevention reported. Hospitals are also learning how to treat COVID-19 patients better, Adalja said.

He noted that hospitalizations are increasing in places like Texas and Arizona, where data from those states show twice as many people or more in hospitals for COVID-19 treatment than there were in early June. That may indicate the virus’ moving beyond younger populations into those more at risk of suffering serious effects.

Whether the spikes happening in the South and West presage a resurgence of the virus in Pennsylvania and New Jersey is uncertain, Adalja said. Those states have been more measured in their reopening plans and have already experienced a surge, while some of the states now suffering had not yet contended with serious outbreaks.

The preventive steps he recommended are by now familiar refrains: Wear a mask. Wash hands. Keep distance from others.

» READ MORE: What is ‘contact tracing’ and why is it back in vogue for tracking coronavirus?

Contact tracing will also be important to prevent outbreaks in the region from spreading, and to detect where the virus is going.

“I know that the virus, it moves very quickly from one populace to another,” Farley said. “A week or two from now, it could be different.”

Looking back on her bout with COVID-19, Tomaszewski remembers most how isolating it was. She was scared, but was careful to stay away from her mother, and only saw her husband in person once over about six weeks.

“Your natural reaction is to want to reach out to people and be near them and be with them, and you have to kind of fight that urge,” she said. “It’s just so lonely.”

Seeing people ignore the seriousness of the virus is personal to her.

“I have to say it’s like a little bit of a slap in the face. I feel like it kind of diminishes everything I went through, and then on top of it there are people who have lost their lives,” she said.

“There’s all these signs it’s very serious, and I’m standing right in front of you, so take me seriously. Listen to what I’m saying.”