A look back at samples of patients with flu-like symptoms in the central Chinese city of Wuhan has uncovered signs of coronavirus outbreaks in the wider community in early January – well before the public was even told the pathogen was contagious.
The coronavirus emerged in late December as a mysterious respiratory infection in dozens of patients, many of them linked to the Huanan Seafood Wholesale Market in the city.
Local health authorities initially thought the patients were sickened through exposure to a common infection source in the market and ruled out the pathogen as contagious until January 20.
It is still unclear whether the wholesale market was the source of the outbreak or a breeding ground for the virus to spread among more people.
The virus has since swept across the planet and infected 1.4 million people, killing more than 80,000.
Researchers with the Wuhan Centre for Disease Control and Prevention looked at patient samples from October 6 until January 21 to search for undetected cases of Covid-19, the disease caused by the virus.
They analysed 640 throat swabs collected from young and adult patients with influenza-like illnesses – all outpatients with a sudden onset of a fever higher than 38 degrees Celsius and a cough or sore throat.
Nine adult samples tested positive for the Sars-CoV-2, the previously unknown coronavirus. One of 40 samples taken from two Wuhan hospitals on January 4 tested positive. There were three positive swabs among samples taken the next week and five the following week.
“Although the weekly sample size was small, it seems that Covid-19 was gradually expanding among the influenza-like illness cases during January,” the researchers, led by Liu Manqing, wrote in a paper published in Nature Microbiology on Tuesday.
“Interestingly, the nine patients with Covid-19 came from six different districts of the Wuhan metropolitan and surrounding areas, which provided additional evidence for community transmission in this region.”
The city imposed an unprecedented lockdown to curb the spread of the virus on January 23. The lockdown was lifted on Wednesday but measures are still in place inside the city to prevent further outbreaks.
Wuhan has been monitoring influenza-like illnesses and their causes since 2005 as part of the national influenza surveillance network.
Two hospitals from the network, the Children’s Hospital of Wuhan and Wuhan No 1 Hospital – a major general hospital with more than 2 million outpatient visits per year – were chosen for the study.
The surveillance in Wuhan was suspended in late January because CDC labs and hospitals concentrated instead on handling the overwhelming medical needs created by Covid-19.
Such retrospective analysis has also been conducted in other parts of China, according to a report by the WHO-China Joint Mission, after a group of Chinese and foreign experts visited China for eight days in February.
In the southern province of Guangdong, from January 1 to 14 only one of more than 15,000 influenza-like illness and severe acute respiratory infection samples tested positive for the new coronavirus.
In one hospital in Beijing, there were no Covid-19 positive samples among 1,910 collected from January 28, 2019, to February 13, 2020.
Sign up now and get a 10% discount (original price US$400) off the China AI Report 2020 by SCMP Research. Learn about the AI ambitions of Alibaba, Baidu & JD.com through our in-depth case studies, and explore new applications of AI across industries. The report also includes exclusive access to webinars to interact with C-level executives from leading China AI companies (via live Q&A sessions). Offer valid until 31 May 2020.
More from South China Morning Post:
- Coronavirus: low antibody levels raise questions about reinfection risk
- Wuhan doctors plan long-term look at coronavirus impact on male sex hormone
- Thousands of covert coronavirus cases go under the radar in Wuhan, Chinese-led researchers say
This article Signs that coronavirus was spreading in Wuhan earlier than thought, study finds first appeared on South China Morning Post