Objective  To analyze the reporting profile of mass unknown-cause disease events from 2004 to 2018 in China, so as to provide suggestions for improving it’s reporting quality.

  Methods  A descriptive analysis was conducted based on the database of mass unknown-cause disease events reported through the Public Health Emergency Management Information System from 2004 to 2018.

  Results  Twenty nine provinces across the country (excluding Hong Kong SAR, Macao SAR and Taiwan province) reported 271 mass unknown-cause disease events from 2004 to 2018. 242 events reported with mass unknown-cause disease events while 29 with other kinds of diseases or events initially. 125 events were finally revised to other types of events after investigation, which accounted for 46.13% (125/271). In total 271 events, 183 events (67.53%) had a clear finding on the causes after investigation, which were infectious diseases (48.63%, 89/183), other public health events (33.88%, 62/183), poisoning events (8.74%, 16/183) and environmental events (6.56%, 12/183). The 242 events which initially reported as mass unknown-cause disease events concentrated in 2004 to 2009 (90.91%, 220/242), and mostly reported by Center for Disease Control and Preventions(CDCs) (77.19%, 176/228) while hospitals were the major information sources (85.57%, 166/194), and those events mainly occured in the places where people gathered like schools (73.11%, 155/212). The result of reporting quality analysis showed that primary medical and health institutions detected and reported events in the shortest durations, which was 5.00 days interquartile range (IQR): 0.73−14.04 and 0.99 day (IQR: 0.54−2.26) respectively. Among the 146 events which still kept the type of mass unknown-cause disease event, 32.19% (47/146) were ungraded events, 79.80% (79/99) were classified to third most serious level. The completeness rate of attachments to the first report and the final report was 52.05% (76/146).

  Conclusion  The reports of mass unknown-cause disease events had obvious time aggregation in China. A large proportion of reported events eventually had a cause identified. The standardability of reporting still need to be improved in the future even though the reporting quality on detection and reporting as well as the completeness rate of attachments to the first report and the final report have been improved since 2004.