Daily reports of new COVID-19 cases on the Diamond Princess cruise ship, quarantined near Yokohama with thousands trapped aboard, have raised a question: Why can't Japan test all passengers at once?

According to the cruise operator, 2,666 passengers and 1,045 crew members were aboard the ship, which has been in Yokohama since Feb. 3 and has since been placed under a two-week quarantine. With the health ministry's announcement Wednesday of an additional 39 confirmed cases on the ship, the total number of people infected aboard rose to 174. The tally for the domestic cases outside the ship is 29.

Health minister Katsunobu Kato said Wednesday his ministry will seek measures to screen everyone aboard the ship but Japan apparently has had its hands tied, as the number of test kits to diagnose the new coronavirus has been limited, in addition to logistics difficulties.