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The coronavirus pandemic has sickened more than 2,425,000 people, according to official counts. So far at least 164,000 people have died, and the virus has been detected in at least 177 countries, as the following table shows.

New Delhi, Fevb 10: Of the countries most at risk of importing coronavirus cases, India ranks 17th, researchers have found on the basis of a mathematical model for the expected global spread of the virus that originated in China's Wuhan area in December 2019.

So far, India has reported three coronavirus positive cases -- all from Kerala.

Among the airports in India, the Indira Gandhi International Airport in New Delhi is most at risk, followed by airports in Mumbai, Kolkata, Bengaluru, Chennai, Hyderabad and Kochi, according to the model.

The new model for predicting global novel coronavirus cases has been developed by researchers from Humboldt University and Robert Koch Institute in Germany.

"The spread of the virus on an international scale is dominated by air travel," said the study.

"Wuhan, the seventh largest city in China with 11 million residents, was the relevant major domestic air transportation hub with many connecting international flights before the city was effectively quarantined on January 23, 2020, and the Wuhan airport was closed. By then the virus had already spread to other Chinese provinces as well as other countries," it added.

The researchers said that it is possible to estimate how likely it is that the virus spreads to other areas by looking at air travel passenger numbers.

"The busier a flight route, the more probable it is that an infected passenger travels this route. Using these probabilistic concepts, we calculate the relative import risk to other airports. When calculating the import risk, we also take into account connecting flights and travel routes that involve multiple destinations," said the study.

The top 10 countries and regions at risk of importing coronavirus cases are: Thailand, Japan, South Korea, Hong Kong, Taiwan, USA, Vietnam, Malaysia, Singapore and Cambodia, according to the model.

While Thailand's national import risk is 2.1%, it is 0.2% for India, found the research.

The foundation of the model is the worldwide air transportation network (WAN) that connects approximately 4,000 airports with more than 25,000 direct connections.

The model accounts for both, the current distribution of confirmed cases in mainland China as well as airport closures that were implemented as a mitigation strategy.

This network theoretic model is based on the concept of effective distance and is an extension of a model introduced in the 2013 paper "The Hidden Geometry of Complex, Network-Driven Contagion Phenomena" published in the journal Science.

The current outbreak of the 2019-nCoV virus started in Wuhan city, Hubei province, China. While the first cases were reported as early as December 8, 2019, the outbreak gained global attention on December 31, 2019, when the World Health Organization was alerted to "several cases of pneumonia" by an unknown virus.

The new virus was soon identified as a novel coronavirus and named 2019-nCOV. It belongs to the family of viruses that include the common cold and viruses such as SARS and MERS. On January 20, 2020, it was confirmed that the coronavirus can be transmitted between humans, greatly increasing the risk of a global spread.

The death toll due to the novel coronavirus outbreak in China has increased to 811 on Sunday, surpassing that of the Severe Acute Respiratory Syndrome (SARS) epidemic in 2003.

Although about 20 countries have confirmed cases, China has accounted for about 99 per cent of those infected. The first foreign victims of the virus both died on Saturday in Wuhan.

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.