Background
Current COVID-19 policy in China, “zero tolerance for local transmission”, implies stopping all imported outbreaks and maintaining elimination of SARS-CoV-2. There has been importation-related local outbreak in Nanjing city in July, 2021. On 29 July, two COVID-19 cases were identified in Zhangjiajie. We initiated a joint investigation to identify infection source and contain the outbreak.
Methods
Our outbreak investigation and response was guided by the Protocol for Prevention and Control of COVID-19, 8th edition. Infections were confirmed by RT-PCR. Traditional face-to-face interviews, augmented with cellphone location technology, were used to trace close contacts, followed by quarantine and daily RT-PCR testing. Travel restrictions, environmental disinfection, population-wide PCR screening, and virus genome sequencing were key containment measures.
Results
The outbreak was notified by Dalian that three travelers from Zhangjiajie passed through Nanjing airport and tested positive on arrival in Dalian. Eleven streets were immediately identified as risk areas, and residents were home quarantined. With more infections were identified, all other residents were city quarantined for 14 days. A total of 13,217 primary or secondary contacts of COVID-19 cases were identified, separately quarantined in 105 facilities, PCR-tested, and placed under health surveillance. Four thousand workers conducted ten rounds of RT-PCR screening (n=6.71 million tests, three whole-city and seven high-risk-areas) in 1,800 screening sites during 28 July through 23 August. Travel restrictions stranded 1,227 tourists for hotel quarantine. In total, 76 Delta-variant COVID-19 cases were identified: 6 from 786,459 city isolation persons (0.008‰); 28 from 456,008 home quarantine personnel (0.06‰); 42 from 13,217 quarantined close contacts (3.2‰). Infections among community and quarantined people were cleared within 14 and 18 days respectively.
Conclusion
The Zhangjiajie outbreak was triggered by Dalian travelers infected in Nanjing. Thorough implementation of the 8th edition Protocol stopped this outbreak within 18 days, helping to maintain elimination of SARS-CoV-2.