Months after the coronavirus infected more than 700 people on board the Diamond Princess cruise ship in Japan, scientists are still gleaning insights into the patterns of illness it causes.

Almost a fifth of the 3,711 passengers and crew on the 13-deck luxury ship in February caught the virus -- most of them showing no tell-tale symptoms of Covid-19 at the time.

A detailed analysis of cases found the disease could be very mild, causing a sore throat, dry cough and runny nose, without fever or lower respiratory tract symptoms, a study published in the June edition of the journal Emerging Infectious Diseases showed.

That’s problematic and differs with early reports that described Covid-19 manifesting as pneumonia, according to researchers in Japan. “Most cases are milder and could have more transmission potential because patients might not seek medical attention,” said Takeshi Arashiro, a junior resident at the Asahi General Hospital in Chiba, just outside Tokyo.

Early reports described Covid-19 manifesting as pneumonia, “but most cases are milder and could have more transmission potential because patients might not seek medical attention,” said Arashiro, who is also a collaborating researcher with the Infectious Diseases Surveillance Center in the National Institute of Infectious Diseases in Tokyo.

The lower threshold for testing people for the coronavirus while the cruise ship was quarantined in Yokahama “created an opportunity to observe mild Covid-19 cases and monitor patient symptoms,” he said.

Understanding the disease pattern that coronavirus infection can cause is important for informing strategies for detecting and controlling it.

The high proportion of people who test positive for the virus and have only mild or no symptoms makes fever-screening travelers, for example, much less useful in detecting probable infections than was the case with the related coronavirus that caused severe acute respiratory syndrome 17 years ago.

Here is a breakdown of the cases on the Diamond Princess:

The Diamond Princess, owned by Carnival Corp., departed Yokohama on May 16 for Malaysia, NHK reported last week.