It has been nearly 1 year since the beginning of the coronavirus disease 2019 (COVID-19) pandemic, the pathogen of which has been identified as COVID-19 virus (also known as SARS-CoV-2, 2019-nCoV, or HCoV-19) (1–2). The spread of the virus has led to a global health crisis (3). China has taken effective measures to suppress COVID-19. However, it still faces a huge challenge of detecting and dealing with imported cases (4).
This investigation was for an imported case that was detected on November 15, 2020 by Qingpu CDC, Shanghai. With the detection of this case, one of the most important tasks was an epidemiological investigation that could provide key information for screening close contacts of this case. The case was promptly sent for isolation and treatment, and the close contacts were sent to an isolated place for active and effective medical observation. The results of this investigation might benefit future surveillance efforts and mitigate the risk caused by the imported cases.
There is an incubation period in COVID-19 infection before symptoms appear. The incubation period is normally from 1 to 14 days, mostly 3 to 7 days (5–6). After the incubation period, some infectees will show clinical symptoms. During the incubation period, the infected person has no symptoms but has a certain level of contagiousness. If appropriate isolation is not carried out, the infectee will become a potential reservoir of the infection. Therefore, during the epidemic, in order to counter the spread of COVID-19 infections, the government should require all people with a clear epidemiological contact history to self-quarantine for 14 days (7).
We conducted an epidemiological investigation on the case from November 15 to 16. Based on the self-reported travel experience of the patient and her mother and the isolation status of other passengers, we had made the following inferences about the possibility of the patient being infected with COVID-19, as shown in Table 1. Based on the investigation, we inferred that this case was most likely infected with COVID-19 during the yard sale event in the United States. The guests on Halloween night may also be a possible source of transmission. In addition, the potential risk of being infected while waiting for the flight cannot be ruled out. The risk of infection for other passengers on the flight increased due to the presence of asymptomatic infections. The possibility of infection in the aircraft could also be nonnegligible depending on the flight range, in which a longer period of flight would increase the risk of transmission. For example, the toilets on the aircraft become humid and messy when used by many people, which might create conditions for the transmission. The toilet space on the plane was slightly narrow, which greatly increased the risk of infection during the prolonged flight. The investigator stated that she had visited the bathroom many times during the flight. In this investigation, all the other passengers on the flight were not positive during the 14-day quarantine period, and there had been no reports of related infections since then. However, this reminds us that the “toilet incident” might be a loophole of prevention and control on the airplane that is worth taking appropriate countermeasures for. For example, disinfection supplies should be equipped in the toilets of the aircraft and warning signs should be posted in the corresponding places to remind passengers to disinfect appropriately.
Investigation Events Reason Risk level First investigation* 1 The patient contacted many customers alone for about 3–4 minutes and half of the customers did not wear a mask, but the patient wore a mask. Extremely high 2 The patient entertained 4 visitors alone during Halloween and opened the door twice. But the visitors did not enter the door and both the patient and the visitors wore masks. Medium 3 Neither the patient’s mother nor American friends had symptoms. Low 4 The patient basically stayed with the mother and wore masks, but she spent about 5 minutes buying 2 bottles of water when waiting for the flight. Medium 5 The patient went to the bathroom about 7–8 times and took off the mask 1–2 times in the bathroom to wash her face. The patient reported that the bathroom environment was messy in the later stages of the flight. High 6 All passengers had no abnormal symptoms. The patient and other passengers wore masks. Low Follow-up investigation† 1 As mentioned in the first investigation. Extremely high 2 As mentioned in the first investigation. Medium 3 End of the 14-day quarantine period, the mother’s nucleic acid test was negative. The friend had not shown any signs. Very low 4 As mentioned in the first investigation. Medium 5 The nucleic acid tests of other passengers on the flight were negative. After the 14-day quarantine period, no other positive cases of the flight. Very low 6 After the 14-day quarantine period, no other positive cases were found among the passengers on the bus Very low * The basis for judgment: the epidemiological survey report from November 15 to 16.
† The basis for judgment: on November 27, the passengers of this flight had met the 14-day quarantine and were discharged.
Table 1. The potential routes and risk levels of the patient’s COVID-19 infection at different events during the transition from US to China.
The laboratory diagnosis of this case indicated that comprehensive judgment based on clinical and test results was important. Except for nucleic acid detection, the detection of antibodies (8) and CT scans (9) played an important role in the determination of COVID-19. The first two tests for antibodies (IgG and IgM) of the patient were negative, which suggested that the patient was in an early stage of onset. The results of the first CT scan could also be verified accordingly. However, the positive test results of the ORF1a/b and N genes of COVID-19 in the sputum specimen of this patient indicated that the subject had the ability to spread the virus. On the seventh day in the SPHCC, the results of the CT scan of the patient were also normal, which might be due to early case detection and treatment. In addition, monitoring and management during isolation were also of great importance. The patient recovered after 17 days of treatment. In order to ensure safety, the subject was quarantined for another 14 days. This person has since been discharged from isolation.
So far, COVID-19 is still raging around the world. With the large-scale resumption of work and production of Chinese enterprises, the prevention and control of COVID-19 are still facing huge challenges from imported cases and locally sporadic cases caused by the imported cases or cold chain transport (10). An efficient multisectoral collaboration mechanism and a sensitive surveillance and response system will greatly contribute to prevention and control of the COVID-19.