Health officials in China have published the first details of more than 70,000 cases of Covid-19, in the biggest study since the outbreak began.

Data from the Chinese Centre for Disease Control and Prevention (CCDC) found that more than 80% of the cases have been mild with the sick and elderly most at risk.

The research also points to the high risk for medical staff.

The findings put the overall death rate of the Covid-19 virus at 2.3%.

In Hubei, the worst affected province, the death rate is 2.9% compared with only 0.4% in the rest of the country. 

China's latest official figures released on Tuesday put the overall death toll at 1,868 and 72,436 infections.

Officials said there were 98 new deaths and 1,886 new cases in the past day, 93 of those deaths and 1,807 of the infections were in Hubei province - the epicentre of the outbreak.

More than 12,000 people have recovered, according to Chinese authorities.

What does the study tell us?

The paper by the CCDC, released on Monday and published in the Chinese Journal of Epidemiology, looked at all 72,314 cases of Covid-19 diagnosed across China as of 11 February, including confirmed, suspected, and asymptomatic cases.

While the results largely confirm previous descriptions of the virus and patterns of infection, the study includes a detailed breakdown of the 44,672 confirmed cases across all of China.

Some of the conclusions reached include the following:

• Some 80.9% of infections are classified as mild, 13.8% as severe and only 4.7% as critical.
• The highest fatality rate is for people aged 80 and older, at 14.8%.
• For children up to 9, there have been no fatalities and up to the age of 39, the death rate remains low at 0.2%.
• For the next age groups, the fatality rates increase gradually: For people in their 40s it is 0.4%, in their 50s it is 1.3%, in their 60s it is 3.6% and their 70s it is 8%.
• Looking at the sex ratio, men are more likely to die (2.8%) than women (1.7%).
• Identifying which existing illnesses put patients at risk, the study finds cardiovascular disease at number one, followed by diabetes, chronic respiratory disease and hypertension

Pointing out the risk for medical staff, the paper says that a total of 3,019 health workers have been infected, 1,716 of which were confirmed cases and five had died by 11 February, which was the last day of data included in the research.

On 13 February, China broadened its definition of how to diagnose people, including "clinically diagnosed cases" which previously were counted separate from "confirmed cases".

What does it say about the future?

Looking forward, the paper found that "the epidemic curve of onset of symptoms" peaked around 23-26 January before declining up to 11 February.

The study suggests that the downward trend in the overall epidemic curve could mean that "isolation of whole cities, broadcast of critical information  (e.g., promoting hand washing, mask wearing, and care seeking) with high frequency through multiple channels, and mobilization of a multi-sector rapid response teams is helping to curb the epidemic".

But the authors also warn that with many people returning from a long holiday, the country "needs to prepare for the possible rebound of the epidemic".

China's response to the virus has seen the lockdown of Wuhan - the largest city in Hubei - and the rest of the province as well as severe travel restrictions on movements across the country.

What's happening with the cruise ships?

The virus has spread beyond mainland China to countries around the globe and two cruise ships are now confirmed to have been affected.

The Diamond Princess was quarantined in the Japanese port of Yokohama on 3 February, after a man from Hong Kong tested positive. More than 450 of the 3,700 people on board have since become infected.

The US has begun evacuating its citizens from the vessel.

On Tuesday South Korea joined the list of the countries also planning to get their residents out which already includes Canada, Australia, Israel and Hong Kong.

A second ship, the MS Westerdam was turned away by multiple ports around Asia over fears it could be carrying the virus.

It was finally cleared to dock in Sihanoukville, Cambodia, after no cases were found on board. Disembarking passengers were personally welcomed by Prime Minister Hun Sen. No one was quarantined.

However days later, a woman who had been on the ship tested positive after arriving in Malaysia. Huge efforts are now being made to track down the passengers, who have moved on to many different countries including Malaysia and Thailand, but also further afield to US and Canada.

Several countries have said they will not admit foreign visitors who were on the ship.

There are still 255 guests and 747 crew on board the MS Westerdam, while more than 400 passengers have been sent to a hotel in the capital, Phnom Penh, to await test results. BBC