https://ojs.wpro.who.int/ 1WPSAR Vol 12, No 3, 2021 | doi: 10.5365/wpsar.2021.12.3.808 Brief Report C oronavirus disease 2019 (COVID-19) is a respiratory illness caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2), first identified in December 2019 in Hubei Province, China.1 By 31 January 2020, at least one case had been reported from each of mainland China’s 31 provincial-level administrative units, and by 29 February, a total of 80 968 cases had been reported.2 On 30 January 2020, WHO declared COVID-19 a public health emergency of international concern, and on 11 March 2020, WHO declared the outbreak a global pandemic. Non-pharmaceutical interventions (NPIs) for res- piratory virus outbreaks are used to prevent exposures and reduce transmission through individual or community action.3,4 With several other countries in the Western Pacific Region,5–7 China implemented COVID-19 contact tracing with quarantine as part of a comprehensive COVID-19 prevention and control strategy, which also included mask use, emphasis on hand hygiene, enforced physical distancing and movement restrictions within and between provinces.8,9 China’s contact-tracing strategy was to identify and quarantine exposed individuals to prevent additional disease transmission. On 20 January 2020, China des- ignated COVID-19 a notifiable disease and updated the “Frontier Health and Quarantine Law” to allow quarantine of contacts.10 National guidelines on epidemiological a United States Centers for Disease Control and Prevention, Atlanta, GA, United States of America. b United States Centers for Disease Control and Prevention, China Country Office, Beijing, China. c United States Public Health Service Commissioned Corps, Rockville, MD, United States of America. Published: 12 August 2021 doi: 10.5365/wpsar.2021.12.3.808 Objective: Contact tracing has been used in China and several other countries in the WHO Western Pacific Region as part of the COVID-19 response. We describe COVID-19 cases and the number of contacts traced and quarantined per case as part of COVID-19 emergency public health response activities in China. Methods: We abstracted publicly available, online aggregated data published in daily COVID-19 situational reports by China’s National Health Commission and provincial health commissions between 20 January and 29 February 2020. The number of new contacts traced by report date was computed as the difference between total contacts traced in consecutive reports. A proxy for the number of contacts traced per case was computed as the number of new contacts traced divided by the number of new cases. Results: During the study period, China reported 80 968 new COVID-19 cases and 659 899 contacts. In Hubei Province, there were 67 608 cases and 264 878 contacts, representing 83% and 40% of the total, respectively. Non-Hubei provinces reported tracing 1.5 times more contacts than Hubei Province; the weekly number of contacts traced per case was also higher in non-Hubei provinces than in Hubei Province and increased from 17.2 in epidemiological week 4 to 115.7 in epidemiological week 9. Discussion: More contacts per case were reported from areas and periods with lower COVID-19 case counts. With other non-pharmaceutical interventions used in China, contact tracing and quarantining large numbers of potentially infected contacts probably contributed to reducing SARS-CoV-2 transmission. Use of public data to describe COVID-19 contact tracing in Hubei Province and non- Hubei provinces in China between 20 January and 29 February 2020 Emilio Dirlikov,a Suizan Zhou,b Lifeng Han,b Zhijun Li,b Ling Hao,b Alexander J. Millmanb,c and Barbara Marstona Correspondence to Emilio Dirlikov (email: klt9@cdc.gov) WPSAR Vol 12, No 3, 2021 | doi: 10.5365/wpsar.2021.12.3.808 https://ojs.wpro.who.int/2 Dirlikov et alCOVID-19 contact tracing in China as the difference between national totals and totals for Hubei Province. Ethics statement This activity was deemed not to be research as defined in United States Government 45 CFR 46.102(l), and institutional review board approval was not required. Non-research determination was provided by the US CDC Center for Global Health in May 2020. RESULTS In addition to national and Hubei Province data, complete data were available for 22 of 30 non-Hubei provincial-level administrative units: Anhui, Chongqing Municipality, Gansu, Guangxi Autonomous Region, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hunan, Inner Mongolia Autonomous Region, Jiangsu, Jiangxi, Jilin, Liaoning, Qinghai, Shaanxi, Shandong, Shanxi, Tianjin Municipality, Tibet Autonomous Region and Zhejiang (Fig. 1). Eight provinces, comprising 26% of the total population, were excluded from the analysis because of no or insufficient reported data (Beijing Municipality, Fujian, Guangdong, Ningxia Autonomous Region, Shanghai Municipality, Sichuan, Xinjiang Au- tonomous Region and Yunnan). During epidemiological weeks 4–9, the NHC report- ed 80 968 new COVID-19 cases and 659 899 contacts traced. These included 67 608 cases (83% of total cases reported) and 264 878 contacts (40% of total reported contacts traced) in Hubei Province. During the same pe- riod, non-Hubei provinces reported an aggregate total of 13 360 cases and 395 021 contacts traced. Among the 22 provinces with provincial-level data, those with the largest numbers of reported cases and contacts traced were Henan Province (reported cases = 1274/9664 [13%]; reported contacts = 39 199/306 684 [13%]) and Zhejiang Province (reported cases = 1216/9664 [13%]; reported contacts = 41 050/306 684 [13%]). The weekly number of contacts traced per case remained <10 in Hubei Province throughout the study period (median = 6.45; range = 2.0 in epidemiological week 7 to 8.5 in epidemiological week 4); the lowest value occurred when 18 453 clinically diagnosed cases were reported as part of the case counts for 12–15 February (epidemiological week 7), which increased the investigations and management of contacts were issued and updated several times, and responsibility for contact tracing was delegated to the local level.11,12 The national guidelines defined contacts as: “anyone who may have had contact with a case through a range of circumstances or activities including being family members, relatives, friends, colleagues, classmates, health care workers, and services personnel”.12 The national guidelines further detailed eight categories of close contacts (e.g. family members living together, direct caregivers or providers of medical treatment or care services and other people considered by onsite investigators to meet the criteria for a close contact). To describe the number of contacts traced and quar- antined per case as part of COVID-19 emergency public health response activities, we compared data from Hubei Province with those from the 30 other mainland provinces (non-Hubei provinces) reported between 20 January and 29 February 2020. We compared the numbers in Hubei Province with those in non-Hubei provinces because the majority of reported cases occurred in Hubei Province. METHODS We abstracted publicly available, online aggregated data reported in daily situational reports at the national level by the NHC and provincial level by provincial health commissions (see Appendix: data sources). For epide- miological weeks 4–9 (weeks ending on Saturdays), we collected daily reported data on newly reported cases and total contacts traced and placed under medical observation. Data were reviewed for abstraction errors, including data entry errors and data completeness. Provincial data that were >95% complete (i.e. reporting for >95% of days between 20 January and 29 Febru- ary) were included. When situational reports included corrections to reported data, the corrected data were used for the day reported. The number of new contacts traced by report date was computed as the difference between the total num- ber of contacts traced on consecutive reports. A proxy for the number of contacts traced per case was computed as the number of new contacts traced divided by the number of new cases. Calculations were performed by epidemiological week. Data were analysed at national and provincial levels (in the included provinces) and for the 30 non-Hubei provinces combined, calculated https://ojs.wpro.who.int/ojs/index.php/wpsar/article/view/808/1044 WPSAR Vol 12, No 3, 2020 | doi: 10.5365/wpsar.2021.12.3.808https://ojs.wpro.who.int/ 3 COVID-19 contact tracing in ChinaDirlikov et al identifying pre-symptomatic and asymptomatic infec- tions early and reducing the time from symptom onset to initiation of medical care.13,14 Contact tracing and data reporting varied by prov- ince, with non-Hubei provinces reporting more contacts traced per case, and the number of contacts traced per case in these provinces increasing during the study pe- riod. In Hubei Province, the average number of contacts traced per case remained <10 during this period, and the number of contacts traced decreased with increas- ing numbers of reported cases. Although non-Hubei provinces reported only 17% of total cases, 1.5 times more contacts were traced than in Hubei Province. The differences between provinces may reflect local capacity for contact tracing, differences in local disease transmission, evolving guidelines and implementation of other NPIs. For example, a lockdown in Wuhan City began on 23 January 2020, followed by widespread movement restrictions within and between provinces1 to mitigate transmission; national travel restrictions began to be lifted on 17 February 2020, although movement restrictions continued. Implementation differed among provinces.9 denominator substantially and consequently reduced the number of contacts traced per case (Fig. 2 and Table 1). The weekly number of contacts traced per case was higher in non-Hubei provinces than in Hubei Province and increased from 17.2 in epidemiological week 4 to 115.7 in epidemiological week 9 (Fig. 2 and Table 1). Data from the 22 non-Hubei provinces indicated that the number of contacts traced per case generally increased as case counts declined, while the reported number of contacts traced either remained high or increased over time. For example, Anhui Province reported 60 cases and 1023 contacts traced during epidemiological week 4 (17.1 contacts traced per case) and 1 case and 915 reported contacts traced during epidemiological week 9 (915 contacts traced per case). DISCUSSION With other NPIs used in China, contact tracing and quarantining of a large number of potentially infected contacts probably contributed to reducing SARS-CoV-2 transmission.10 Contact tracing with quarantine po- tentially helped to mitigate the risk of transmission by Hubei Province Non-Hubei provinces Excluded provinces Fig. 1. Map of mainland China provinces included in the analysis WPSAR Vol 12, No 3, 2021 | doi: 10.5365/wpsar.2021.12.3.808 https://ojs.wpro.who.int/4 Dirlikov et alCOVID-19 contact tracing in China observation, housing for contacts and laboratory testing capacity. While contact tracing identified and isolated large numbers of potentially infected contacts, pub- lished studies show that most contacts did not become reported cases: 30.4% (391 positive contacts/1286 contacts traced) in Shenzhen, 2.6% (129/4950) in Guangzhou and 2.3% (120/5241) in Xi’an.13–15 Contact tracing with quarantine is resource inten- sive. For example, in Wuhan City, contact tracing was conducted by 1800 epidemiologists working in teams of five.8 Data on provincial contact-tracing resources were not available. Geographical and temporal differ- ences may have affected the availability of resources, including trained staff for contact tracing and medical Fig. 2. Reported numbers of COVID-19 cases and contacts traced per case, by week, Hubei Province (red) and non-Hubei provinces (calculated; blue), epidemiological weeks 4–9, 2020 The weekly number of contacts traced per case was calculated as the number of new contacts traced in an epidemiological week divided by the number of new cases reported in that week. Data for the 30 non-Hubei provinces were calculated as the difference between national totals and totals for Hubei Province. In Hubei Province, the lowest value occurred when 18 453 clinically diagnosed cases were reported in case counts for 12–15 February (epidemiological week 7), which increased the denominator substantially and consequently lowered the number of contacts traced per case. 17.2 Non-Hubei provinces (calculated) Epidemiological week 5000 6000 22.8 27.6 45.3 40.2 115.7 20.0 00 New cases N ew c as es Number of contacts per case N u m b er o f co n ta ct s p er c as e 40.0 60.0 80.0 100.0 120.0 1000 4 5 6 7 8 9 2000 3000 4000 8.5 Hubei Province Epidemiological week 30 000 35 000 5.1 4.2 2.0 7.8 8.2 2.0 00 New cases N ew c as es Number of contacts per case N u m b er o f co n ta ct s p er c as e 4.0 6.0 8.0 10.0 10 000 5000 4 5 6 7 8 9 15 000 20 000 25 000 WPSAR Vol 12, No 3, 2020 | doi: 10.5365/wpsar.2021.12.3.808https://ojs.wpro.who.int/ 5 COVID-19 contact tracing in ChinaDirlikov et al comprehensive in areas and periods with lower case counts (non-Hubei provinces); there may also have been differences in other NPIs implemented, including mask use, emphasis on hand hygiene, enforced physical distancing and movement restrictions. Future investigations should better define the role of COVID-19 contact tracing and quarantine, including timeliness, prioritization of contacts who are more likely to be associated with transmission and the effectiveness of contact tracing in contexts that differ epidemiologi- cally, socially and with respect to resource availability. Acknowledgements We thank RJ Simonds for administrative and technical support. Conflicts of interest None of the authors has a conflict of interest. Funding No funding was given for this activity. Disclaimer (required for publication by CDC authors): The conclusions, findings and opinions expressed by au- thors contributing to this journal do not necessarily reflect the official position of the US Department of Health and Human Services, the US Public Health Service or the US Centers for Disease Control and Prevention. This report has several limitations. First, the public data did not include contact-by-exposure type, and it is likely that the actual number of contacts traced differed by type of exposure (e.g. family, shopping centre, public transport). Therefore, the number of “contacts traced per case” may be overestimated when large numbers of contacts are linked to a single case (e.g. attending a public gathering with a confirmed case). Second, with- out data on individual patients, our analysis is based on aggregated data and subject to ecological fallacy. For example, contacts traced reported in one week could have been those of cases reported in the previ- ous week. Third, data on contact-tracing outcomes and resources were not available for analysis. All contacts were assumed to have been quarantined according to the national guidelines, and provinces were assumed to have implemented contact-tracing guidelines uniformly, although inter-provincial differences may have affected the comparability of the reported data. The data could not be verified externally, the data collection methods were unknown, and it was not known whether all re- ported contacts traced were linked to reported cases. Finally, reported data on contact tracing were missing or incomplete for eight provinces, which were excluded from the analysis. Despite these limitations, our findings describe contact tracing in China during the COVID-19 response and differences between Hubei Province and non-Hubei provinces based on publicly available data. We found higher rates of contacts traced and quarantined in areas with lower numbers of reported COVID-19 cases, suggesting that contract tracing may have been more Table 1. Weekly numbers of reported COVID-19 cases, contacts traced and contacts traced per COVID-19 case, by geographical unit, epidemiological weeks 4–9, 2020 A proxy for the number of contacts traced per case was computed as the number of new contacts traced divided by the number of new cases. Data for the 30 non-Hubei provinces were calculated as the difference between national totals and totals for Hubei Province. In Hubei Province, the lowest value occurred when 18 453 clinically diagnosed cases were reported in case counts for 12–15 February (epidemiological week 7), which increased the denominator substantially and consequently lowered the number of contacts traced per case. Epi week National total Hubei Province Non-Hubei provinces (calculated) Cases Contacts Contacts per case Cases Contacts Contacts per case Cases Contacts Contacts per case Epi week 4 1748 22 614 12.9 854 7250 8.5 894 15 364 17.2 Epi week 5 12 410 140 413 11.3 8022 40 582 5.1 4388 99 831 22.8 Epi week 6 22 843 208 061 9.1 18 026 75 256 4.2 4817 132 805 27.6 Epi week 7 32 447 157 513 4.9 30 279 59 356 2.0 2168 98 157 45.3 Epi week 8 8437 99 099 11.7 7409 57 754 7.8 1028 41 345 40.2 Epi week 9 3083 32 199 10.4 3018 24 680 8.2 65 7519 115.7 Total 80 968 659 899 8.2 67 608 264 878 3.9 13 360 395 021 29.6 WPSAR Vol 12, No 3, 2021 | doi: 10.5365/wpsar.2021.12.3.808 https://ojs.wpro.who.int/6 Dirlikov et alCOVID-19 contact tracing in China References 1. Pan A, Liu L, Wang C, Guo H, Hao X, Wang Q et al. Association of public health interventions with the epidemiology of the COV- ID-19 outbreak in Wuhan, China. JAMA. 2020;323(19):1915–23. doi:10.1001/jama.2020.6130 pmid:32275295 2. 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ISSN:1671–8259/CN:61–1399/R. http://weekly.chinacdc.cn/news/TrackingtheEpidemic2020.htm http://weekly.chinacdc.cn/news/TrackingtheEpidemic2020.htm https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-repor https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-repor WPSAR Vol 12, No 3, 2020 | doi: 10.5365/wpsar.2021.12.3.808https://ojs.wpro.who.int/ 7 COVID-19 contact tracing in ChinaDirlikov et al Technical Appendix. Provincial-level health commission websites containing publicly available reported data on COVID-19 Province Name Location National Health Commission http://weekly.chinacdc.cn/news/TrackingtheEpidemic.htm Anhui http://wjw.ah.gov.cn/ Beijing http://wjw.beijing.gov.cn/xwzx_20031/xwfb/ Chongqing http://wsjkw.cq.gov.cn/ Fujian http://wjw.fujian.gov.cn/ Gansu http://wsjk.gansu.gov.cn/ Guangdong http://wsjkw.gd.gov.cn/zwyw_yqxx/index.html Guangxi http://wsjkw.gxzf.gov.cn/gzdt/bt/ Guizhou http://www.gzhfpc.gov.cn/ Hainan http://wst.hainan.gov.cn/swjw/index.html Hebei http://wsjkw.hebei.gov.cn/ Heilongjiang http://wsjkw.hlj.gov.cn/ Henan http://www.hnwsjsw.gov.cn/ Hubei http://wjw.hubei.gov.cn/fbjd/dtyw/ Hunan http://wjw.hunan.gov.cn/ Inner Mongolia http://wjw.nmg.gov.cn/ Jiangsu http://wjw.jiangsu.gov.cn/ Jiangxi http://hc.jiangxi.gov.cn/ Jilin http://wsjkw.jl.gov.cn/ Liaoning http://wsjk.ln.gov.cn/ Ningxia http://wsjkw.nx.gov.cn/ Qinghai https://wsjkw.qinghai.gov.cn/ Shaanxi http://sxwjw.shaanxi.gov.cn/ Shandong http://wsjkw.shandong.gov.cn Shanghai http://wsjkw.sh.gov.cn/xwfb/index.html Shanxi http://wjw.shanxi.gov.cn/ Sichuan http://wsjkw.sc.gov.cn/scwsjkw/szyw/tygl.shtml Tianjin http://wsjs.tj.gov.cn/ Tibet http://wjw.xizang.gov.cn Xinjiang http://xjhfpc.gov.cn Yunnan http://ynswsjkw.yn.gov.cn/wjwWebsite/web/index Zhejiang http://www.zjwjw.gov.cn/col/col1202101/index.html http://weekly.chinacdc.cn/news/TrackingtheEpidemic.htm http://wjw.ah.gov.cn/ http://wjw.beijing.gov.cn/xwzx_20031/xwfb/ http://wsjkw.cq.gov.cn/ http://wjw.fujian.gov.cn/ http://wsjk.gansu.gov.cn/ http://wsjkw.gd.gov.cn/zwyw_yqxx/index.html http://wsjkw.gxzf.gov.cn/gzdt/bt/ http://www.gzhfpc.gov.cn/ http://wst.hainan.gov.cn/swjw/index.html http://wsjkw.hebei.gov.cn/ http://wsjkw.hlj.gov.cn/ http://www.hnwsjsw.gov.cn/ http://wjw.hubei.gov.cn/fbjd/dtyw/ http://wjw.hunan.gov.cn/ http://wjw.nmg.gov.cn/ http://wjw.jiangsu.gov.cn/ http://hc.jiangxi.gov.cn/ http://wsjkw.jl.gov.cn/ http://wsjk.ln.gov.cn/ http://wsjkw.nx.gov.cn/ https://wsjkw.qinghai.gov.cn/ http://sxwjw.shaanxi.gov.cn/ http://wsjkw.shandong.gov.cn http://wsjkw.sh.gov.cn/xwfb/index.html http://wjw.shanxi.gov.cn/ http://wsjkw.sc.gov.cn/scwsjkw/szyw/tygl.shtml http://wsjs.tj.gov.cn/ http://wjw.xizang.gov.cn http://xjhfpc.gov.cn http://ynswsjkw.yn.gov.cn/wjwWebsite/web/index http://www.zjwjw.gov.cn/col/col1202101/index.html