- The novel coronavirus was first identified in the Chinese city of Wuhan, in December 2019.
- Although the city reported itself coronavirus free in late April of 2020, a recent study states otherwise.
- Researchers estimate that some 168,000 people may have been infected in Wuhan; around 3 times higher than the actual number.
Since its emergence in December 2019, SARS-CoV-2 has managed to infect over 90 million people worldwide. The first case of the novel coronavirus was discovered in the Chinese city of Wuhan, which later went on to become the epicenter of the pandemic. Furthermore, around two-thirds of all COVID-19 cases in China came from Wuhan. The city declared itself free of coronavirus in late April. However, a recently published study suggests that COVID-19 may have remained in Wuhan longer than expected.
Thousands of Asymptomatic COVID-19 Cases in Wuhan
Researchers from Wuhan University published the study in PLOS Neglected Tropical Diseases. They analyzed 63,107 samples collected in China between March and May of 2020. The samples belonged to people from Wuhan and other parts of China; all healthy individuals who underwent routine screening before returning to work. The researchers studied the samples for IgG and IgM antibodies.
IgM antibody signifies current or recent infection; whereas the presence of IgG suggests previous infection. They can both give an estimate of the infection rate for a disease in a population. IgM antibodies help detect asymptomatic infections of COVID-19.
The analysis showed that 1.68% of samples from Wuhan contained antibodies against coronavirus. A percentage that was much higher than areas outside of the Hubei province and the rest of China. Furthermore, the IgM positivity rate was around 0.5% in Wuhan as compared to 0.07% in other areas of China. Thus, indicating the high level of asymptomatic infections in the region.
We conclude that … a large amount of asymptomatic carriers of SARS-CoV-2 existed after elimination of clinical cases of COVID-19 in Wuhan City,
study authors
Actual COVID-19 Cases in Wuhan 3 times Higher
Based on the positive antibody rate and Wuhan’s population of more than 10 million, researchers estimate that 168,000 people in Wuhan may have been infected in the city during the outbreak. An estimate that is almost 3 times higher than the actual reported number of 50,340 cases.
Moreover, the high level of IgM antibodies suggests that the virus likely existed in thousands of asymptomatic individuals long after the outbreak was declared over in the city. However, researchers question what could have caused a high number of asymptomatic cases. The authors of the study hypothesize it’s likely because of attenuated viral strains. China’s strict screening protocols along with hospitalization of symptomatic individuals likely resulted in avirulent viral strains. Since avirulent strains can revert back to a virulent one, researchers warn against a possible resurgence in the city.
A 10-member team from the World Health Organization (WHO) is currently in Wuhan to investigate the origin of the virus.
References:
Duan S, Zhou M, Zhang W, Shen J, Qi R, Qin X, et al. (2021) Seroprevalence and asymptomatic carrier status of SARS-CoV-2 in Wuhan City and other places of China. PLoS Negl Trop Dis 15(1): e0008975.
https://doi.org/10.1371/journal.pntd.0008975
