Japan has confirmed two more cases of coronavirus among the citizens it evacuated from Wuhan, highlighting the uncertainty around diagnosing the disease and the possibility of lengthy incubation periods.

One case, a man in his 50s, returned to Japan on the first evacuation flight on January 29th. He tested negative on January 30th and went into quarantine. On February 7th, he developed a fever and was admitted to hospital, but again tested negative for the virus. He finally tested positive on February 10th.

Another case, a man in his 40s, was on the second evacuation flight and returned to Japan on January 30th. He also tested negative and went into self-quarantine at home. On February 8th, he developed a fever and took over-the counter medicine, which reduced his temperature. But on the 10th, an x-ray showed pneumonia in both lungs. He was admitted to hospital and tested positive for the virus.