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More cases of asymptomatic virus carriers emerge as southwest Japan city expands testing

A worker at a drive-thru polymerase chain reaction test center in Kitakyushu, Fukuoka Prefecture, collects a sample from a passenger in a car, on May 2, 2020. (Mainichi/Takuya Inoue)

FUKUOKA -- The southwestern Japan city of Kitakyushu in Fukuoka Prefecture is seeing a recent surge in the number of new COVID-19 cases due to an expanded checkup system where those who had close contact with the infected people but are showing no symptoms have now become subject to coronavirus testing.

    As the Ministry of Health, Labor and Welfare advised local governments at the end of May to carry out polymerase chain reaction (PCR) tests on all those who had close contact with coronavirus carriers, discoveries of such "hidden patients" could continue in areas that are seeing positive test results.

    The city of Kitakyushu reported no new coronavirus cases for 23 consecutive days from April 30, but has been seeing new cases every single day since May 23. Of the 97 people who had tested positive for the virus between May 23 and May 31, infection routes for 34 were unknown, while the remaining 63 were those who had close contact with those 34 people, including their co-workers and friends. Of those 63 people, 46 were showing no symptoms at the time of their PCR tests. Of the 34 people with unknown transmission routes, six were asymptomatic but had tested positive after being suspected to have pneumonia while they were in hospital for other illnesses.

    Until recently, Kitakyushu's policy was to have those who did not show symptoms stay home for two weeks even if they were family members or co-workers of the infected people with symptoms. Fearing that such asymptomatic people could spread the virus by going out while not knowing that they had been infected, however, the city expanded the scope of subjects for PCR tests to all those who had close contact with carriers when new cases were reported for the first time in 24 days. The city opened a drive-thru PCR test center on May 2, which also helped expand testing.

    As a result, coronavirus carriers who could have possibly gone undetected under the previous policy have started showing up in numbers. At Moritsune Elementary School in the city's Kokuraminami Ward where five students tested positive, all but one student who first was confirmed to have the virus were asymptomatic. A senior city official explained that the growing number of confirmed cases was "something expected when we expanded test subjects."

    As the number of new cases has stabilized and public health centers now have more room to respond to requests, the expansion of PCR testing is a move seen across the country. Starting on May 7, the city of Kyoto began testing all those who had close contact with infected people and managed to detect virus carriers.

    The health ministry on May 29 told prefectural governments and other local bodies to test all residents who had close contact with COVID-19 patients, saying that research at home and abroad has shown that the infected people could start transmitting the virus two to three days before they start developing symptoms. A health ministry official says the move was aimed at detecting coronavirus carriers quickly.

    (Japanese original by Eijiro Matsuda, Takuya Inoue and Emi Aoki, Kyushu News Department)

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