Wuhan is the capital of Hubei Province and a megacity in central China. After the COVID-19 epidemic occurred in December 2019, strong prevention and control measures were taken to prevent the epidemic from spreading. Based on the stochastic transmission model, Adam J Kucharski showed that the median daily reproduction number in Wuhan declined from 2.35 (95% CI 1.15–4.77) 1 week before travel restrictions were introduced on Jan 23, 2020, to 1.05 (0.41–2.39) 1 week after6. Research by Wang Xuyan showed that the COVID-19 epidemic in Hubei Province has gradually eased from mid to late February, and the prevention and control measures were very effective7. As of February 24, 2020, the number of daily deaths in Wuhan has shown a clear downward trend.
In the composition of deaths, mild type accounted for the largest proportion, 37.2%, followed by severe type deaths, accounting for 30.1%, and the initial diagnosis of the dead with underlying diseases is mostly mild type, so we should be alert to the deterioration of mild type.
Judging from the age distribution of diagnosed cases across the country, people of all ages are not resistant to the COVID-195. The analysis of the expert group also supported this view8. Older people and those with underlying diseases such as asthma, diabetes and heart disease may be at increased risk of contracting the virus9. In our study, 65.7% of the deaths in Wuhan combined with underlying diseases, the main combined underlying diseases were hypertension, diabetes and cardiovascular diseases. Studies have shown that combination with underlying diseases such as hypertension, diabetes and cardiovascular disease may increase the mortality rate of COVID-19 patients10–12. It may be because the metabolic syndrome can downregulate the key mediator of the host's innate immune response to pathogenesis, affecting the function of the innate and humoral immune systems13. In addition, the pathogen of COVID-19, SARS-COV-2, is mainly bound to target cells by angiotensin-converting enzyme 2(ACE2) and ACE1 drugs are often used in cardiovascular disease patients, and long-term use of ACE1 can up-regulate the expression of ACE2 receptors in the body14. Thiazolidinedione in hypoglycemic drugs can also cause upregulation of ACE2 expression15, which may aggravate the patient's symptoms.
The deaths in Wuhan were mainly middle-aged and elderly people, mainly concentrated in the age group of 50–89 years. It may be due to the weaker physical resistance of the middle-aged and elderly people and the higher probability of combining the underlying diseases. The minimum age of deaths is 14 years old, and no 0–9 years old deaths occurred. SARS also has a low impact on children, considering the commonness of coronaviruses, children may be relatively unsusceptible to COVID-19 based on cellular structure or immunity16. There are no reports of COVID-19 causing maternal and infant deaths. In addition, the possibility of vertical transmission of coronavirus is very low. There are no recorded cases of vertical transmission of SARS or MERS17,18, and the COVID-19 has not been confirmed vertical transmission 19–21.
The male to female ratio of national confirmed is 1.06: 1 issued by the China CDC and 0.99: 1 in Wuhan, which indicates that men and women are equally susceptible to COVID-19. However, the fact that the sex ratio of deaths in Wuhan is 1.95: 1 shows male patients have a higher risk of death. As coronaviruses, SARS and COVID-19 have similar sex differences, probably because the X chromosome and estrogen can protect women from fatal infections22,23 .
Among all occupational categories, the number of retirees’ deaths was the largest, accounting for 46.8%. And medical staff and family members of patients often have close contact with patients during treatment, nursing, accompanying and visiting patients, the risk of nosocomial infection is high. Among the deaths, the number of deaths caused by nosocomial infection is 14, accounting for 0.8% of the total deaths. Children and students accounted for the least percentage of deaths, at 0.1%. Studies have shown that the SARS-CoV-2 can use multiple homologous genes of angiotensin converting enzyme II (ACE2) to effectively replicate in human respiratory tract cells 24. The relatively low incidence of child deaths may be due to the relatively weak function of ACE2 receptors in children, or low expression, which limits the path of viral invasion and avoids large-scale outbreaks in children16.
Analysis of 1833 deaths in Wuhan found that the mean interval from onset to diagnosis was 11.2 days; the median time was 10.0 days. Moreover, the interval from onset to diagnosis gradually shortened. For deaths with onset before January 15, between January 15–31 and after January 31, the median interval from onset to diagnosis is 15.0d, 11.0d and 5.0d, respectively, indicating that the ability to discover and diagnose COVID-19 cases has gradually improved. And the deaths of different severity classifications have similar interval from onset to diagnosis, from diagnosis to death, and from onset to death.
According to the death data as of February 24, the first case of COVID-19 death in Wuhan was located in Huangpi District. The geographical map showed the distribution of COVID-19 epidemic in Wuhan had obvious regional differences. The central urban area was more serious than the surrounding urban areas. The cumulative deaths reported in the central urban area accounted for 82.8%. Wuchang District was the most serious, followed by Jiang'an District and Jianghan District. The death rate of COVID-19 in Wuhan was also the highest in the central urban area. This regional difference may be due to the fact that the Huanan Seafood Wholesale Market, the outbreak point, was located in Jianghan District, and the traffic in the central urban area was convenient, and the designated COVID-19 hospitals in the early stage of the epidemic were also located in the central urban area.
This study also has some limitations. First, some variables in this study have missing records, which may slightly affect the results. Second, this study traced the patients’ death outcome to February 24, when many patients had not yet had disease outcomes. Third, the onset date of this study was obtained from the patient's self-report, and there may be a recall bias.
In summary, the COVID-19 posed a greater threat to the elderly and more men than women, especially elderly men with underlying diseases. The geographical distribution showed that the epidemic in the central area of Wuhan is more serious than in the surrounding areas. The reduction in the interval from onset to diagnosis also indicates a gradual improvement in the ability to detect and diagnose COVID-19 cases. The number of daily deaths in Wuhan had continued to decline after February 14, indicating that the COVID-19 epidemic in Wuhan has achieved a tremendous improvement, and the strong epidemic control measures taken by Wuhan Government were very effective.