TOKYO >> Day after day, the rising number of new cases of the coronavirus in Tokyo and across Japan is making headlines. But what is even more alarming is the increasing number of instances in which authorities can’t track where patients got infected.

Because tracing the source of infection is vital in curbing an outbreak, the situation is sparking concern that infections in Japan may get as out of control as they have in Western countries.

In early April, experts from a government-appointed panel said that in 40% of reported cases, they was no verification of where or when patients contracted the virus.

In Tokyo, that figure is ominously higher. Of a record 197 new cases reported Saturday, sources of infection couldn’t be tracked in 77% of cases.

The same trend has been seen in Fukuoka and Osaka prefectures, which, along with Tokyo, and Aichi and Okinawa prefectures, are seeing daily reports of unknown transmission in 50% to 75% of cases.

One reason for the difficulty is reluctance by some patients to share their whereabouts, said a health ministry official who spoke on condition of anonymity.

Shortage of staff at public health centers is another reason.

“Sometimes they struggle with keeping track (when they are overloaded with other tasks),” the official said.

But Paul Hunter, a professor of medicine at the Norwich School of Medicine at the University of East Anglia, says contact tracing is time consuming, and requires specific skills to help patients relay necessary information for tracing.

“It is a skill, contact tracing, because you’ve got to know how to ask people. You’ve got to help them remember places they’d been,” Hunter said. “You have to talk to people over a period of time.”

The government’s lax response in the initial phase of containing the virus may have contributed to the problem.

Diamond Princess passengers, who were quarantined off Yokohama in January and February after other passengers tested positive, were allowed to disembark from the cruise ship on Feb. 19 and, after testing negative, return home using public transportation.

But some of them later tested positive.

“I think Japan made a dreadful mistake with how it handled the Diamond Princess issue,” Hunter said, adding that thorough contact tracing in the early stages of an outbreak can prevent uncontrolled spread.

To some extent, the situation in Japan, with new infections being reported daily all over the country, resembles the issues faced by European countries that have seen a number of COVID-19 patients diagnosed after returning home from Italy.

“The initial problems Italy had in realizing they had a problem effectively seeded the infection around Europe,” Hunter said.

State-of-the-art surveillance technologies used for data tracking, including credit card usage, mobile phones, CCTV, facial recognition and artificial intelligence, can help governments successfully track down COVID-19 patients, although privacy issues are a concern.

But Hunter suggests more proactive testing can be key in grasping the scale of the outbreak.

“Japan certainly hasn’t been testing as much as probably it should,” he said.

“If you do implement these control measures only when it gets out of hand, then it’s too late, without any shadow of a doubt.”