The novel coronavirus, or Covid-19, first emerged in Wuhan city and has spread across the globe in two months, affecting over 20 countries.

Recent news about the incubation period hitting 24 days might have alarmed some of you.

The study which this piece of information came from was actually conducted by over 30 Chinese researchers, including China's top virus expert Zhong Nanshan who later clarified that the 24-day incubation period is an anomaly.

The medical paper was published on Feb. 9 and shares more about the virus infection from a larger pool of confirmed cases, although it has not been peer-reviewed.

Here's a summary of the paper if you want a fuller picture of the findings:

Research based on 1,099 patients

The retrospective study was done based on the data of 1,099 patients from 552 hospitals in 31 provinces recruited as of January 29, 2020.

This sample size is likely by far the largest one for a study on Covid-19.

The information extracted include their exposure history, clinical symptoms, laboratory findings, radiologic assessments.

However, the paper also acknowledged some limitations to this study such as potential incomplete information and not all hospitals involved in this study are equally equipped.

There's also the likelihood that there are asymptomatic or mild cases who managed themselves at home which the study would not be able to include.

The study was approved by China's national health commission.

Key Findings

Here's a summary of the study to help you understand Covid-19 better.

Human-to-human transmission

The median age of infected patients is 47, with 41. 9 per cent being females.

Only 1.18 per cent of the 1,099 patients had direct contact with wildlife.

Most infected patients in this study got contracted through contact with people in Wuhan at 71.8 per cent or had been to Wuhan (31.3 per cent).

This further proved that the Covid-19 is infectious and transmits between humans as observed from the outbreak of family clusters.

Loophole in fever detection

Fever is one of the indications of possible Covid-19 cases which is why temperature screening has been set up.

However, what sets Covid-19 apart from SARS and MERS is the absence of fever among suspected cases at the initial phase.

Notably, about 43.1 per cent of them presented themselves with a fever but 87.9 per cent found with a fever during hospitalisation.

That means temperature screenings can miss out on potential infected patients.

For SARS and MERS, fevers could be detected in most cases, only absent in one or two per cent of patients.

Other symptoms such as coughing, diarrhoea and pneumonia are also reported by the patients in this study before they were confirmed:

• 67.7 per cent had cough.
• 28.1 per cent reported fatigue.
• 3.7 per cent had diarrhea.
• 76.4 percent showed abnormalities in chest CT scan.

Incubation period

In this study, the incubation period is defined as the duration from the contact of the transmission source to the onset of symptoms.

The incubation period ranges from absolutely no incubation to 24 days among the 1,099 patients. However, only one patient had a 24-day incubation period and hence that data point should not be over-interpreted, Zhong told the Chinese media.

The median incubation period was three days. This is shorter than the previously reported five days in a study with a much smaller simple size of 425 patients.

How Covid-19 can be transmitted?

The study found that four out of 62 stool specimens collected tested positive to Covid-19.

Which means beside respiratory droplets and direct contact, this study also shows that the virus can be transmitted via faeces.

Therefore, hygiene protection has to take into account of transmission via gastrointestinal secretions.

Disease severity

Out of the 1,099 patients, 926 are non-severe cases and 173 are severe cases.

Lymphopenia was common and, in some cases, severe among patients involved in this study. About 82.1 per cent of patients developed lymphopenia where the level of lymphocytes (one of the white blood cells) in the body is reduced. 

About 79 per cent develop pneumonia as a complication of the virus infection, most severe cases will have pneumonia.

About five per cent of the patients were been admitted to the intensive care unit.

On average, 1.4 per cent of the 1,099 patients died from Covid-19. These deaths belonged to 0.1 per cent of non-severe cases and 8.1 per cent of the severe cases.

Fatality rate less than 2%

The death rate for Covid-19 is further proven to be lower than SARS and MERS. It is also lower than what was previously estimated at around two per cent.

The lower death rate could be due to the larger sample size used in this study which included 603 patients from Guangdong province, where prevention of Covid-19 has been effective.

Overall, the study shows early isolation, early diagnosis and early management can collectively contribute to a marked reduction in mortality.

China has over 50,000 confirmed cases and around 1,000 deaths reported so far, mostly in Hubei province.

Out of 1241 confirmed cases in Guangdong, two deaths and 314 discharge cases have been reported as of Feb. 13.

Top photo via Shanghai Observer, by Xinhua