COVID-19 cases have been climbing for weeks in New Jersey and soaring in Pennsylvania, which now has daily increases on a par with the peak of the first wave in April.

Yet this worrisome trend has not translated into a surge in hospital admissions in New Jersey and Pennsylvania, as it did in the spring.

The same paradoxical situation has occurred in other parts of the United States and in some European countries. The coronavirus has produced conflicting data on how quickly a jump in cases impacts hospitals, and how severe that impact is.

That raises an all-important question: Can the spread of the virus increase — unflattening the curve — without overburdening hospitals?

The answer, experts say, is complicated.

For one thing, diagnostic testing has ramped up since the pandemic began. The ability to detect more infections, including those that don’t produce symptoms, drives up the case numbers, but it also enables public health workers to squelch an outbreak quickly with contact tracing and quarantine measures. Officials in both Pennsylvania and New Jersey say the rate of tests that come back positive is below 5%, the World Health Organization’s benchmark for having transmission under control.

However, Pennsylvania’s has been edging toward that benchmark, climbing to more than 4% as of Friday. New Jersey’s positivity rate remains lower.

“In the initial phases of the pandemic in the spring, there was limited testing capacity, so only the most symptomatic people were tested and they tended to be further along in their illness,” said Donald Yealy, senior medical director and chair of emergency medicine at the University of Pittsburgh Medical Center. “Now, we’re detecting the virus in people who are younger and less sick. And we know how to manage patients better, so fewer wind up in the ICU.”

Some experts speculate that certain variants of the virus have become less virulent, but that hasn’t been proved. What has been proved is that precautions — social distancing, avoiding crowds, washing hands, and especially masking — can reduce transmission of the virus.

The problem, of course, is that as people resume more and more normal activities and cold weather drives them indoors, there will be safeguard slip-ups and riskier gatherings.

“There is a lot more activity than in the spring,” said P.J. Brennan, chief medical officer of the University of Pennsylvania Medical System. “People are back in schools, athletic activities have resumed, people are dining out, and we’re indoors more.”

For many weeks, Penn Medicine has had an average of about 40 COVID-19 patients in its six hospitals, including the West Philadelphia flagship, compared with 10 times that many in the spring, Brennan said. Meanwhile, a steadily increasing number of Penn outpatients have been diagnosed with the infection.

“I think all of us are waiting for the other shoe to drop,” Brennan said. “Reopening [businesses] comes with a price, and the price is more cases.”

David Rubin, the physician who leads a pandemic modeling project at Children’s Hospital of Philadelphia, said hospitals in the center of the state, particularly around Pennsylvania State University, have been seeing an increase in COVID-19 admissions. With the Thanksgiving holiday ahead, Rubin worries that intergenerational family gatherings could put vulnerable seniors at risk.

“There is some level of vigilance that may be keeping the hospitalizations down,” particularly in Southeastern Pennsylvania, he said. “But maybe it’s only a matter of weeks before that changes."

Roberto Caricchio, chief of rheumatology at Temple’s Katz School of Medicine, said the cautiousness of the elderly is reflected in the low level of hospitalizations.

“The population at greater risk of becoming ill is much more careful," he said. “I have countless elderly patients who have not been in [physical] contact with their younger family members since April. But if we lower our guard, we will end up as in March.”

Yealy added, “We now know that in addition to big super-spreader events, the other risky situation is a micro-party: family dinners, small weddings, funerals."

In any case, Pennsylvania and New Jersey health officials and pandemic tracking groups report plenty of room in the states’ hospitals, and more important, in intensive-care units, where ventilators would be used for the most critically ill patients.

Pennsylvania has about 4,196 ICU beds, with 12% of them needed by current COVID-19 patients, according to estimates by CovidActNow, a nonprofit, volunteer organization. Even with 57% of ICU beds now in use by non-COVID-19 patients, that leaves “enough capacity to absorb a wave of new COVID infections.”

The same is true in New Jersey, where CovidActNow estimates that 32% of the state’s 833 ICU beds are currently occupied by COVID-19 patients, and 36% are filled by non-COVID patients, leaving 32% available.

“I do think there is a lag" between a surge in cases and an impact on hospitals, said Yealy at Pitt. “But even if admissions go up, I don’t think hospitals will get overwhelmed."

Staff writer Tom Avril contributed to this report.