(Fixes typo in para 6, in story originally published January 30.)
By Reuters Staff
(Reuters Health) - An analysis of the first 425 cases of the new coronavirus wreaking havoc in China has concluded it typically takes 5.2 days for an infected person to show symptoms, the epidemic has been doubling in size every 7.4 days, the deadly disease is spreading pneumonia through human-to-human contact, and a growing number of healthcare workers are becoming infected.
The coronavirus, designated 2019-nCoV, has infected more than 7,800 people, mostly in China, and 170 have died from confirmed infections.
But that rate could decline dramatically as health officials gather more information, including testing to see how many people may have survived the illness without seeking medical help. The researchers behind the new report say there have apparently been many mild cases of the illness.
There is no vaccine or cure.
The new study, released by the New England Journal of Medicine, is based on the first confirmed cases in Wuhan, China, a city of 11 million people that has been shut down by the pandemic since January 23. Neighboring cities have also been subject to quarantine.
The 5-day incubation period supports the strategy of putting exposed people in quarantine or under observation for 14 days, said the research team, led by Dr. Zijian Feng of the Chinese Center for Disease Control and Prevention in Beijing.
The outbreak has been traced to the Huanan Seafood Wholesale Market, where an exotic array of animals are sold as food. It was closed on January 1. The first person to fall ill who had a connection to the market became sick on December 13.
Among the cases identified in December, 55% were linked to the market. Since then, only 8.6% have been tied to the market, offering evidence for human-to-human spread.
Doctors originally identified the outbreak as they searched for a cause for four cases of "pneumonia of unknown etiology," all of which were traced to the market.
The growth rate was estimated from illnesses that began between December 10 and January 4.
Surprising, there were no cases among children under age 15, either because they are somehow less likely to be infected or because they may show milder symptoms, the researchers said.
The first case from Wuhan seen outside China was identified in Thailand on January 13. Two days later, China's Centers for Disease Control and Prevention raised the country's response level to Level 1, its highest.
The number of cases seen among health care workers has been increasing. Health workers were responsible for 8 out of 122 cases, or 7% from January 12-22, up from 3% between January 1-11. But those rates are lower than in outbreaks of SARS, the severe acute respiratory syndrome that caused a major outbreak in 2003, or of MERS, the Middle East respiratory syndrome. Both are caused by coronaviruses.
The Feng team estimated that every infected person was infecting 2.2 other people.
The 2.2 "basic reproduction number," is an estimate of the ease with which a disease can spread through an unprotected population. Viruses with higher numbers spread faster.
For measles, which spreads extremely rapidly, that number is at least 11. For seasonal flu it is 1.3. For Ebola, which is far deadlier than the new coronavirus, it's 2. For SARS, which killed about 9% of its victims, the number is about 3.
"In general, an epidemic will increase as long as (the basic reproduction number) is greater than 1, and control measures aim to reduce the reproductive number to less than 1," the Feng team noted.
The researchers said about one quarter of the people who fell ill sought medical attention within two days. But 89% of the patients didn't make it to the hospital until at least five days had passed.
"This indicates the difficulty in identifying and isolating cases at an early stage of the disease," the Feng group noted.
There is also limited evidence that, instead of developing pneumonia, some infected people may develop gastrointestinal symptoms.
SOURCE: https://bit.ly/37GkNQF The New England Journal of Medicine, online January 29, 2020.