COVID-19: Early transmission dynamics in Wuhan, China, of novel coronavirus-infected pneumonia
COVID-19: Early transmission dynamics in Wuhan, China, of novel coronavirus-infected pneumonia.
Spencer E, Jefferson T, Heneghan C.
Published on June 16, 2020
Transmission Dynamics of COVID-19
COVID-19 transmission was occurring since mid-December 2019 in Wuhan: the majority in the Huanan Seafood Wholesale Market. A lack of early testing may have missed cases, particularly those with atypical symptoms.
The data relates to cases diagnosed up until 22 January 2020.
- The majority of early cases in Wuhan were linked to Huanan Seafood Wholesale Market.
- Mean incubation period was estimated at 5.2 days (95% CI 4.1 to 7.0). At that early stage, the number of cases doubled every 7.4 days.
There was an exponential increase in the number of cases not linked to the Huanan Seafood Wholesale Market from late December onwards. Twenty percent of cases had exposure to another person with respiratory symptoms (85% of cases, however, had no exposure to a market or a person with respiratory symptoms).
There were no cases in under 15-year-olds; over half (56%) of the 425 cases were in adults ≥60 years of age. Children were considered less likely to become infected or, if infected, show milder symptoms, which might account for their underrepresentation. Fifteen (3.6%) of the infected cases were healthcare workers.
Source: N Engl J Med 2020; 382:1199-1207 DOI: 10.1056/NEJMoa2001316
What did they do?
This study analysed data on the first 425 cases of novel coronavirus-infected pneumonia (NCIP) diagnosed in hospitals in Wuhan, Hubei province, China to determine initial epidemiological descriptors and indicators of transmission dynamics.
Local and centralised Centers for Disease Control agencies provided data on diagnoses. Cases and their relatives, close contacts and healthcare workers were interviewed to collect demographic, exposure history, and illness timelines. Places visited by the patient (including households, work locations and public spaces including markets) two weeks prior to disease were investigated for possible animal and environmental exposures. The authors report characteristics of cases, estimates of time from exposure to diagnosis.
This is descriptive data from an early stage in the epidemic and is not reproducible. Interpretation of the speed of the epidemic growth is limited by the availability and use of the testing kit, which increased over time. Confirmed cases were more identifiable after the PCR tests were made available to Wuhan on January 11th. Early infections with atypical presentations may also have been missed.
|Clearly defined setting
||Demographic characteristics described
||Follow-up length was sufficient
||Transmission outcomes assessed
||Main biases are taken into consideration
What else should I consider?
This was a useful study to begin to understand where infections arose and transmission occurred. Since then more data has been gathered from other studies which aid our understanding of transmission. The authors note that both SARS and MERS outbreaks saw the occurrence of super-spreading events, particularly in hospitals.
About the authors
Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings
Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.
Tom Jefferson, epidemiologist.