Guidelines for COVID-19 Epidemiological Investigations

1. To investigate source of infection and trace and identify close contacts;

2. To investigate onset of illness and treatment of patients, including clinical characteristics and risk factors;

3. To investigate and analyze transmission characteristics of COVID-19 cases and clusters of cases.

The guidelines cover investigation of COVID-19 suspected cases, confirmed cases, asymptomatic infected persons, and clusters of cases.

The county (district) level disease control and prevention agency, upon receiving a report of one or more COVID-19 cases, should complete an initial epidemiological investigation within 24 hours. The investigation can be conducted through review of documents and interviews with patients, physicians, acquaintances, and others as needed. When a patient has completed a 14-day period of isolation and health monitoring, the county (district) level disease control and prevention agency should obtain information on specimen collection and testing for inclusion in the case report.

Case investigation should include basic demographic and identification data and information on onset of symptoms, care-seeking behavior, risk factors, potential exposures, and laboratory findings of suspected cases, confirmed cases, and asymptomatic infected persons. For suspected cases, this information is to be recorded in a Case Investigation Questionnaire (Appendix S1) that includes identifying information such as name, gender, and ID number. Information about individuals identified as close contacts should be recorded in the Health Status Monitoring Case Form for Close Contacts in the Guideline for Investigation and Management of Close Contacts of COVID-19 Cases.

A cluster of cases is the detection of 2 or more confirmed cases or asymptomatic infected persons in a small area (e.g., in a family, an office, a school class, or workplace) within a 14-day period and that has the possibility of person-to-person transmission or a common exposure.

Based on case reports in the Infectious Disease Reporting Information Management System (IDRIMS) and case investigation findings potentially meeting the above definition, the county (district) level disease control and prevention agency should immediately launch an investigation into a possible cluster of cases. Investigations should include information on source of infection and close contacts. The investigation should focus on epidemiological links among cases; chains of transmission and transmission routes should be analyzed. For investigation and analytic methods, refer to Appendix S2.

Using the principle of “localized management,” health authorities of the county or district where the individual being investigated sought medical care shall have the disease control and prevention agency conduct an epidemiological investigation of the case or cluster of cases. The investigating agency should promptly establish an investigation team, clarify the purpose of the investigation, develop an investigation plan, select team members, and assign duties and tasks. During all investigations, investigators should use proper personal protective equipment. Professionals from disease control and prevention agencies at the prefecture, provincial, and national levels should accompany county or district level teams when requested or when deemed necessary.

Upon completion of an investigation of confirmed cases, asymptomatic infected persons, or cluster of cases, the county (district) level disease control and prevention agency should submit a case investigation form or investigation report to the online reporting system. The local CDC should review the submitted report and update it in a timely manner as the investigation progresses.

For investigations of clusters of cases, all basic information and all initial, interim, and final reports should be submitted in accordance with the National Protocol for Reporting and Management of Public Health Emergency Related Information (Trial). All key information of these investigations (see Appendix S2) should be included in the final report.

Acknowledgement: China CDC Weekly would like to thank Xijuan Fu of the WHO China Office, Canjun Zheng, Liping Wang, Zhaorui Chang, Zhongjie Li, Lance Rodewald, and Huilai Ma of China CDC for their contributions in translating and editing this document (1).

The Chinese document written by experts in China CDC Strategy and Policy Working Group for COVID-19 Emergency Response, including Zijian Feng of China CDC, Canjun Zheng, Zhaorui Chang, Fengfeng Liu, Mengjie Geng, Junling Sun, Sheng Zhou, Lu Ran, Huilai Ma, Liping Wang, Zhongjie Li of Division of Infectious Disease, Key Laboratory of Surveillance and Early Warning on Infectious Disease, China CDC, Hui Chen of National Center for Tuberculosis Control and Prevention, China CDC, Jingwei Jiang of National Institute for Communicable Disease Control and Prevention, China CDC, and Jian Li of National Center for AIDS Control and Prevention, China CDC.