Can you imagine 61 infected people on that cruise ship? This can prove infectious diseases can spread on a cruise ship so fast!
The same air is circulating all over the ship though ventilators. People have to breathe the same air as Coronavirus infected people exhaled. People use many public spaces including toilets. 3700 people are board? That’s like a floating small city. Those 3700 people use share the same area, and Coronavirus spread one by one by contaminated air, food&water and spaces.
And still people are on that cruise ship waiting to be evacuated. But they cannot enter Japan unless they are 100% free from Coronavirus. Now, US Government wants to evacuate those US citizens on board.