[Epidemic dynamic model based evaluation of effectiveness of prevention and control strategies for COVID-19 in Ningbo].

Objective: To evaluate effectiveness of prevention and control strategies for COVID-19 in Ningbo by using an epidemic dynamic model. Methods: The incidence data and epidemic information of COVID-19 reported in Ningbo as of 9 March, 2020 were collected, and based on the implementation of prevention and control strategies, we developed a SEIR epidemic dynamics model. The basic and real-time reproduction numbers were calculated to evaluate effectiveness of prevention and control. Results: A total of 157 cases of COVID-19 were confirmed, without death, in Ningbo. The proportion of severe cases was 12.1%. The mean incubation period was estimated to be (5.7±2.9) days. The mean interval from illness onset to diagnosis was (5.4±3.7) days. The mean duration from diagnosis to hospital discharge was (16.6±6.5) days. A total of 105 339 contacts had been under medical observation. The infection rates in contacts with home quarantine and centralized quarantine were 0.1% and 0.3%, respectively. In the confirmed cases, those who had been under medical observation before diagnoses accounted for 63.1%. The basic reproduction number was estimated to be 4.8. With the strengthening of prevention and control measures, real-time reproduction number showed a gradual downward trend, dropping to below 1.0 on 4 February, and then continued to drop to 0.2 in mid-February. Conclusion: The effectiveness of the prevention and control measures for COVID-19 in Ningbo can be evaluated by using epidemic dynamic model to provide scientific evidence for the development of the prevention and control strategies.

[Epidemiological characteristics of infection in COVID-19 close contacts in Ningbo city].

Objective: To estimate the infection rate of close contacts of COVID-19 cases, and to evaluate the risk of COVID-19 under different exposure conditions. Methods: A prospective study was used to conduct continuous quarantine medical observations of close contacts of people infected with COVID-19, collect epidemiological, clinical manifestations, and laboratory test data to estimate the infection rate of close contacts under different exposures. Results: The epidemiological curve of COVID-19 in Ningbo showed persistent human-to-human characteristics. A total of 2 147 close contacts were tracked and investigated. The total infection rate was 6.15%. The infection rates of confirmed cases and positive contacts were 6.30% and 4.11%, respectively. The difference was not statistically significant (P>0.05). Among close contacts of different relationships, friends/pilgrims (22.31%), family members (18.01%), and relatives (4.73%) have a higher infection rate, and close contacts of medical staff were not infected. Differences in infection rates among the close contacts were statistically significant (P<0.005). Living with the case (13.26%), taking the same transportation (11.91%), and dining together (7.18%) are high risk factors for infection. Cross-infection in the hospital should not be ignored (1.94%). The median of incubation period is 5 days. Conclusion: The infection rate of close contacts of COVID-19 cases is high, and isolation medical observation measures should be implemented in strict accordance with the close contact management plan.