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.
目的： 估算新型冠状病毒肺炎病例密切接触者的感染率，评估不同暴露状况下新型冠状病毒肺炎的发病风险。 方法： 采用前瞻性研究的方法，对新型冠状病毒肺炎病例和无症状感染者的密切接触者进行持续隔离医学观察，收集流行病学、临床表现和实验室检测资料，估算不同暴露下的密切接触者感染率。 结果： 宁波市新型冠状病毒肺炎发病流行曲线呈现持续的人传人特征。共追踪调查了2 147名密切接触者，总感染率为6.15%，确诊病例、无症状感染者的密切接触者感染率分别为6.30%和4.11%，差异无统计学意义（P>0.05）。不同关系的密切接触者中，以朋友/香客（22.31%）、家庭成员（18.01%）、亲戚（4.73%）感染较高率，医务人员密切接触者未发生感染，各密切接触者人群感染率差异有统计学意义（P<0.005）。与病例同住（13.26%）、乘坐同一个交通工具（11.91%）、聚餐娱乐（7.18%）均是感染高危因素。医院诊疗环境下的交叉感染也不容忽视（1.94%）。潜伏期中位数为5 d。 结论： 新型冠状病毒肺炎病例密切接触者的感染率高，需严格按照密切接触者管理方案实施隔离医学观察措施。.
Keywords: COVID-19; Close contacts; Epidemiological characteristics; Infection rate.