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COVID Papers
Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus–Infected Pneumonia
Reviewed by Charles Li, MD
February 17, 2022
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How COVID-19 gets around
This study analyzed 425 early patients to see how COVID-19 spreads around.
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It takes around 5 days to show
On average, it takes around five days for symptoms to show up in COVID-19 patients after they get infected.
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It spreads to at least 2 people
Researchers estimated that a person with COVID-19 will spread it to around two other people.
Visual Abstract
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Background
Study Quote
The initial cases of novel coronavirus (2019-nCoV)–infected pneumonia (NCIP) occurred in Wuhan, Hubei Province, China, in December 2019 and January 2020. We analyzed data on the first 425 confirmed cases in Wuhan to determine the epidemiologic characteristics of NCIP.
Scientists often use numbers to describe pandemics. These numbers cover features such as how fast a virus spreads, how long it takes to show symptoms, and how dangerous the virus might be.
At the beginning of the COVID-19 pandemic, it was necessary to closely study these first cases in Wuhan to learn more about how the COVID-19 pandemic would eventually play out in the rest of the world.
Methods
Study Quote
We collected information on demographic characteristics, exposure history, and illness timelines of laboratory-confirmed cases of NCIP that had been reported by January 22, 2020. We described characteristics of the cases and estimated the key epidemiologic time-delay distributions. In th...
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Researchers studied 425 of the first patients with COVID-19 in Wuhan in this study. As you may know, COVID-19 was first discovered in Wuhan, a city in China.
By studying these early patients, researchers collected accurate information on their experiences. From these data, researchers were able to calculate key metrics on COVID-19 that are still used today to develop guidelines on COVID-19.
They analyzed information about their symptoms, where they may have been exposed to COVID-19, and information about the patients themselves, such as age and gender.
In the early days of the pandemic, when there were fewer cases of COVID-19 around, researchers were able to pinpoint where patients got exposed to COVID-19 through interviews with close contacts and records of hospital visits.
Results
Study Quote
Among the first 425 patients with confirmed NCIP, the median age was 59 years and 56% were male. The majority of cases (55%) with onset before January 1, 2020, were linked to the Huanan Seafood Wholesale Market, as compared with 8.6% of the subsequent cases. The mean incubation period wa...
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Among the first 425 patients in Wuhan, it took around 5.2 days to develop symptoms of COVID-19.
During this incubation period, COVID-19 virus particles are growing and spread within the body. But, it doesn't cause symptoms, and the patient doesn't feel sick yet.
This estimate is consistent with other high-quality estimates of COVID-19's incubation period.
Researchers estimated that it takes around 7.4 days for COVID-19 to spread, as measured by the serial interval. A serial interval represents the number of days between when an "infector" shows symptoms and when the person they infect will show symptoms.
This number tells us how quickly a disease can spread. A disease with a short serial interval will spread quickly. A disease with a long serial interval will take longer to spread.
Of note, additional studies of COVID-19 have estimated that the serial interval may be closer to 5 days.
Scientists estimated that COVID-19 has a reproductive number of 2.2.
This means that on average, someone with COVID-19 will spread it to around two other people, who can then spread it to two more each.
Based on this number, we can see how COVID-19 can spread from just a few people to thousands in a city.
Conclusions
Study Quote
On the basis of this information, there is evidence that human-to-human trans- mission has occurred among close contacts since the middle of December 2019. Considerable efforts to reduce transmission will be required to control outbreaks if similar dynamics apply elsewhere. Measures to p...
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Study Figures
COVID-19 Hospitalization in Wuhan: On average, it took 9.1 days between illness onset and hospitalization.
The chart above shows the number of days it took for patients to become hospitalized. On average, patients who did have to be admitted to a hospital became hospitalized 9.1 days after their illness onset.
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Infection to Symptom Onset in COVID-19: It took an average of 5.2 days between exposure to and infection with COVID-19 and the first symptoms from COVID-19.
The chart above shows the number of days it took for patients to show symptoms. On average, it took around 5.2 days for patients to show symptoms after they became exposed to and infected with COVID-19.
As you can see on the chart above, most showed symptoms before five days in this particular study. However, the distribution was skewed by a few individuals who took two weeks or longer to show symptoms.