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Houston, Mar 15: Researchers, studying the novel coronavirus, have found that the time between cases in a chain of transmission is less than a week, and over 10 per cent of patients are infected by someone who has the virus, but does not show symptoms yet, a finding that may help public health officials contain the pandemic.

The study, published in the journal Emerging Infectious Diseases, estimated what's called the serial interval of the coronavirus by measuring the time it takes for symptoms to appear in two people with the virus -- the person who infects another, and the infected second person.

According to the researchers, including those from the University of Texas at Austin, the average serial interval for the novel coronavirus in China was approximately four days.

They said the speed of an epidemic depends on two things -- how many people each case infects, and how long it takes cases to spread.

The first quantity, the scientists said, is called the reproduction number, and the second is the serial interval.

Due to the short serial interval of the disease caused by the coronavirus -- COVID-19 -- they said, emerging outbreaks will grow quickly, and could be difficult to stop.

“Ebola, with a serial interval of several weeks, is much easier to contain than influenza, with a serial interval of only a few days,” said Lauren Ancel Meyers, study co-author from UT Austin.

Meyers explained that public health responders to Ebola outbreaks have much more time to identify and isolate cases before they infect others.

“The data suggest that this coronavirus may spread like the flu. That means we need to move quickly and aggressively to curb the emerging threat,” Meyers added.

In the study, the scientists examined more than 450 infection case reports from 93 cities in China, and found the strongest evidence yet that people without symptoms must be transmitting the virus -- known as pre-symptomatic transmission.

More than one in ten infections were from people who had the virus but did not yet feel sick, the scientists said.

While researchers across the globe had some uncertainty until now about asymptomatic transmission with the coronavirus, the new evidence could provide guidance to public health officials on how to contain the spread of the disease.

“This provides evidence that extensive control measures including isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings may be warranted,” Meyers said.

The researchers cautioned that asymptomatic transmission makes containment more difficult.

With hundreds of new cases emerging around the world every day, the scientists said, the data may offer a different picture over time.

They said infection case reports are based on people's memories of where they went and whom they had contact with, and if health officials move quickly to isolate patients, that may also skew the data.

“Our findings are corroborated by instances of silent transmission and rising case counts in hundreds of cities worldwide. This tells us that COVID-19 outbreaks can be elusive and require extreme measures,” Meyers said.

Feb 22: A 20-year-old Chinese woman from Wuhan, the epicentre of the coronavirus outbreak, travelled 400 miles(675 km) north to Anyang where she infected five relatives, without ever showing signs of infection, Chinese scientists reported on Friday, offering new evidence that the virus can be spread asymptomatically.

The case study, published in the Journal of the American Medical Association, offered clues about how the coronavirus is spreading, and suggested why it may be difficult to stop.

"Scientists have been asking if you can have this infection and not be ill? The answer is apparently, yes," said Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, who was not involved in the study.

China has reported a total of 75,567 cases of the virus known as COVID-19 to the World Health Organization (WHO) including 2,239 deaths, and the virus has already spread to 26 countries and territories outside of mainland China.

Researchers have reported sporadic accounts of individuals without any symptoms spreading the virus. What's different in this study is that it offers a natural lab experiment of sorts, Schaffner said.

"You had this patient from Wuhan where the virus is, travelling to where the virus wasn't. She remained asymptomatic and infected a bunch of family members and you had a group of physicians who immediately seized on the moment and tested everyone."

According to the report by Dr Meiyun Wang of the People's Hospital of Zhengzhou University and colleagues, the woman travelled from Wuhan to Anyang on Jan. 10 and visited several relatives. When they started getting sick, doctors isolated the woman and tested her for coronavirus. Initially, the young woman tested negative for the virus, but a follow-up test was positive.

All five of her relatives developed COVID-19 pneumonia, but as of Feb. 11, the young woman still had not developed any symptoms, her chest CT remained normal and she had no fever, stomach or respiratory symptoms, such as cough or sore throat.

Scientists in the study said if the findings are replicated, "the prevention of COVID-19 infection could prove challenging."

Key questions now, Schaffner said, are how often does this kind of transmission occur and when during the asymptomatic period does a person test positive for the virus.

Geneva, May 27: The number of confirmed cases of COVID-19 worldwide has increased by nearly 100,000 over the past 24 hours to surpass 5.4 million, the World Health Organisation (WHO) said.

According to the WHO, the global case tally currently stands at 5,404,512 -- a rise by 99,780 over the past day.

The death count worldwide amounts to 343,514 -- an increase by 1,486.

Most cases of infection are recorded in the Americas -- 2,454,452, with 143,739 deaths.