Day after day, the rising number of new cases of the coronavirus in Tokyo and nationwide is making headlines. But what is even more alarming is the increasing number of instances where authorities can’t track where the patient got it from.

Tracing the source of infection is vital in curbing the outbreak, sparking concerns among medicine and virology experts that the situation in Japan may get out of control like it has in Western countries.

In early April, experts from a government-appointed panel said they were not able to verify where or when patients had contracted the virus in 40 percent of reported cases.

In Tokyo, the figure is ominously higher than the nation’s average. When Tokyo reported a record 197 new coronavirus cases Saturday, 77 percent were cases in which they weren’t able to track down the source of infection.

The same trend has been seen in Fukuoka and Osaka prefectures, which, along with Tokyo and Aichi and Okinawa prefectures, are seeing daily reports where cases of unknown transmission account for somewhere between 50 and 75 percent of the total.

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One of the reasons that the source is difficult to track down is some patients’ reluctance to share their whereabouts with authorities before they started having symptoms, said a health ministry official, who did not reveal his identity in line with ministry policy.

Some of them, the government suspects, may have gone to entertainment facilities, including bars, nightclubs and those offering sexual services, thereby explaining their reluctance.

Shortage of staff at public health centers is also a reason behind the rise in unknown chains of transmission.

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

Normally, public health center officials ask people who have contracted COVID-19 about their travel history and people they came in contact with during the two-week period before they developed symptoms.

But Paul Hunter, a professor of medicine at the Norwich School of Medicine at the University of East Anglia, says it’s easier said than done.

What appears to be a simple task is in fact time consuming and requires certain skills to help patients offer necessary information to track down where they got infected, he said.

“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. You can’t just send somebody to turn up at somebody’s door, knock on their door and say, ‘Can you just answer these three questions?’” 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 also been a cause.

Diamond Princess passengers, who were quarantined off Yokohama port in January and February after one of its passengers tested positive, were allowed to disembark from the cruise ship on Feb. 19 and, after they tested negative, go home using public transportation.

But some of them tested positive afterwards, triggering criticism about the government decision.

“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 could have prevented an uncontrolled spread of the virus.

To some extent, the situation in Japan with new infections being reported on a daily basis 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.

Japan’s health ministry worries that further increases in untraceable sources of coronavirus transmission will only amplify the outbreak across the country.

“We’ll only be able to grasp a small portion of people infected, only to find a massive cluster of infections later,” the health ministry official said.

Marc Windisch, head of the Applied Molecular Virology Lab at the Institut Pasteur Korea, stresses that tracking down as many people exposed to the virus as possible enables governments to take appropriate action in curbing the spread of the virus.

More information on affected and exposed individuals will help the government better inform citizens of possible risks, raising their awareness and encourage them to practice physical distancing or, for instance, wearing a face mask.

Such measures would further result in more testing and detection of infections, leading to more effective isolation of infected patients, he explained.

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

But University of East Anglia’s Hunter suggests more proactive testing using various methods, including neutralizing antibody tests, can be key in grasping the scale of the outbreak.

“If you’re not doing that you are missing the outbreak,” he said.

“Japan certainly hasn’t been testing as much as probably it should. The fact that things are increasing slowly doesn’t mean that you’re going to avoid it. 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.”

RELATED PHOTOS Some who tested positive for the coronavirus but have not revealed their whereabouts in past weeks may have been reluctant to because they went to entertainment facilities, including bars, nightclubs and those offering sexual services. | KYODO