Abstract: Objective To investigate the inapparent infection status in the population in a local outbreak of dengue fever in an island area of Zhejiang province, China, and to provide a scientific basis for determining the size of the epidemic. Methods Sera were collected from asymptomatic individuals in the epidemic area to detect the anti-dengue immunoglobulin M (IgM), and a descriptive statistical analysis was performed on the detection results. Results The first dengue case in Daishan county was reported in JN island on August 30, 2019. A total of 9 cases were reported in this outbreak, all of which were indigenous infections. From August 31 to September 5, 2019, Daishan County Center for Disease Control and Prevention collected 326 serum samples from the asymptomatic population in batches. The inapparent infection rate of the investigated population was 4.91%, and there was no significant difference between males and females (χ²=1.215, P=0.270). The inapparent infection rate in male population was 4.00%, with a significant difference between different age groups (P=0.021). The inapparent infection rate in female population was 6.80%, with no significant difference between different age groups (P=0.127). There was a significant difference in inapparent infection rate between the unemployed group and other occupational groups (χ²=12.240, P<0.001). The positional distribution of dengue cases and inapparently infected individuals was relatively limited within a range of 50 m radius, with high population density, poor sanitary environment, and high mosquito vector density. There had never been an outbreak of dengue fever in the local history, so it can be determined that all positive IgM individuals were caused by primary infection in this outbreak. Conclusion In an outbreak of dengue fever, inapparent infected individuals are more difficult to find out because they are asymptomatic. The number of infected individuals is actually far more than that of patients, which may be an even more important source of infection.

Key words: Dengue fever, Local epidemic, Inapparent infection, Antibody

摘要： 目的 调查一起登革热暴发疫情的人群隐性感染状况，为明确疫情规模提供科学依据。方法 采集疫点内无症状的人群血清，检测登革热IgM抗体，对检测结果进行描述性统计分析。结果 2019年8月30日在岱山县JN岛报告首起登革热病例，该起暴发疫情共报告9例病例，均为本地感染。岱山县疾病预防控制中心于2019年8月31日至9月5日分批次采集无症状人群血清326份，调查人群隐性感染率为4.91%，男女性感染率差异无统计学意义（χ²=1.215，P=0.270）。男性人群隐性感染率为4.00%，不同年龄组间差异有统计学意义（P=0.021）；女性人群隐性感染率为6.80%，不同年龄组间差异无统计学意义（P=0.127）。人群家务待业组与其他职业人群组间差异有统计学意义（χ²=12.240，P<0.001）。病例和隐性感染者分布相对局限于50 m半径距离范围之内，人群密集度高，卫生环境状况较差，蚊媒密度高。该海岛地区历史上从未发生过登革热疫情，可以判定人群IgM阳性者均为此次暴发疫情原发性感染所致。结论 在一起暴发疫情中隐性感染者因为无症状而更难于被发现，感染者数量远多于发病者而可能成为更为重要的传染源。

关键词: 登革热, 本地疫情, 隐性感染, 抗体