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.