As the more contagious variant of the new coronavirus, Omicron, dominates overseas, the risk of contagion from imported items is also a growing concern. The CDC Weekly recently disclosed a local clustered transmission of Omicron that may have been caused by dentures.
Previously, the China Disease Control Weekly reported a case of the clustered transmission of the new crown Omicron variant in Beijing that may have been caused by the mailing of documents in North America.
The paper disclosed that on January 13, 2022, the Center for Disease Control and Prevention of Zhuhai City, Guangdong Province received a notification that a local new crown case was found in the fever clinic of Tanzhou Town, Zhongshan City. On the same day, large-scale nucleic acid testing was carried out in Nanping Town and Qianshan Street, Xiangzhou District, Zhuhai City. A total of 4 new crown cases were found in Nanping Town.
Zhuhai CDC screened 34 positive cases from close contacts of local cases. The Guangdong Provincial Center for Disease Control and Prevention conducted viral gene sequencing on 20 of them, and they were identified as the new coronavirus Omicron variant strain BA.1.
Among the 38 cases of Omicron infection, 76% were mild (26/38) or asymptomatic (3/38), and 24% were new crowns Moderate cases (9/38); 79% of those with mild or asymptomatic infection (23/29) completed more than 2 doses of inactivated vaccine; 83% of infected persons under 15 had mild symptoms (15/29) 18), 70% of adults infected were mild or asymptomatic (14/20). There was no statistically significant difference between the two age groups (P>0.05). The main symptoms of the aforementioned new crown infections were cough (49%, 17/35), fever (29%, 10/35), dry throat (23%, 8/35)). 16% (6/38) of infected patients showed lung inflammation on CT images, 17% (3/18) in children and 15% (3/20) in adults.
Zhuhai CDC found that the outbreak was mainly concentrated in schools, workplaces and families. 
Zhuhai CDC disclosed in the paper, On January 8, 2022, a 34-year-old woman working in Company C developed symptoms and she was the first local case. The situation of the other three members of her family is as follows: her husband is a marina driver, her daughter is studying in elementary school B, and her son is studying in kindergarten A. All three developed symptoms on January 11, 2022.
The epidemic spread from family clusters to kindergartens, elementary schools and companies, and subsequently led to clustered cases in 7 families. The secondary infection rate in the aforementioned households was 15.8%. 
Case Transmission and Intergenerational Interval
The Zhuhai Center for Disease Control and Prevention stated that this clustered outbreak produced five generations of cases. The intergenerational interval was calculated using the time interval between the onset of cases, with a mean of 3.37 days and a standard deviation of 1.70 days. The basic reproduction number (R0) from January 8 to 21 was 1.3 (95% confidence interval: 0.8, 2.0). On January 13, the effective reproduction number (Rt) reached a maximum of 5.5, and after January 19, Rt rapidly dropped below 1. 
Rt value change
In mainland China, Tianjin reported its first imported case of COVID-19 in December 2021. Since February 4, 2020, Zhuhai has had no local COVID-19 cases. The first infected person in the Zhuhai outbreak had never left Zhuhai within a month before the onset of the disease.
Her company C mainly undertakes the customized production of foreign dentures (ie dentures) and dental molds. The goods are imported from Europe and the United States by express. The 34-year-old woman, a customer service employee of Company C, occasionally helped pick up goods in the receiving area without protection (without masks and gloves) between January 1 and 11, 2022.
On January 16, Zhuhai CDC collected 670 environmental samples from Company C and detected 6 positive samples, 5 of which were from infected persons , 1 positive sample came from the inside of the imported mold package on the first floor.
Zhuhai CDC said that after the discovery of new crown cases in surrounding cities, Zhuhai quickly carried out large-scale population screening in nearby areas. Early detection and isolation played a key role in containing the Omicron outbreak. If the epidemic in kindergartens and primary schools is not interrupted in time, it will easily spread in the community and cause an epidemic.
The paper disclosed that although there is no strong evidence that materials other than cold chain food can become the source of infection of the new coronavirus, through epidemiological investigations, the Zhuhai CDC believes that imported dentures and Dental molds may be the source of this outbreak.
According to Southern+ reports, recently, Zhuhai Market Supervision and Administration Bureau has comprehensively strengthened the supervision and inspection of denture production and processing enterprises, and adopted the method of surprise inspection to conduct in-depth field inspections. After investigation, Zhuhai Moumei Dentistry Technology Co., Ltd. violated its responsibility commitment and epidemic prevention and control requirements by privately receiving and processing imported dental molds. On the spot, the supervisors asked them to make immediate changes and resume production only after the rectifications were in place and passed the review.
According to the available data, after the aforementioned outbreak, Zhuhai Market Supervision Bureau implemented classified epidemic prevention and control for denture processing enterprises in the city, and took the lead in printing and distributing the “Zhuhai Dentures” in Guangdong Province. Guidelines for the Prevention and Control of New Coronavirus in Imported Dental Moulds for Production and Processing Enterprises (First Edition)”, which guides enterprises to implement the main responsibility for prevention and control in a standardized and orderly manner, and to do a good job in the prevention and control of epidemics in all aspects such as places, materials, production and processing processes, and personnel. At the same time, efforts were made to increase the frequency and intensity of inspections, to achieve full coverage inspections of 36 denture processing enterprises in Zhuhai City, and to require enterprises to rectify problems such as incomplete training records for high-risk positions found; The post, health and other departments shared information and coordinated work, and dealt with 2 incidents of personal dental clinics receiving overseas dental mold express delivery, and enterprises that had not resumed work receiving imported dental molds, so as to prevent and resolve potential risks in a timely manner.
It is worth noting that on March 19, the State Post Bureau held a video conference, requesting to learn from the recent prominent epidemic-related incidents, and to strengthen epidemic prevention and control in the entire delivery chain. , make up for the shortcomings of the measures. The meeting called for strengthening the prevention of input outside the delivery channel, and implementing the responsibility system for disinfection at the first stop of imported international mail, the rest period before delivery, and the requirements for epidemic prevention reminders for users to receive mail.
A study released recently by the University of Hong Kong also highlights that the Omicron virus can survive for a long time on surfaces. According to the study, the Ormicron variant can spread for 7 days on smooth surfaces such as glass, plastic, and stainless steel.
In fact, in order to prevent and control foreign items from carrying the virus into the country, the Joint Prevention and Control Mechanism of the State Council has issued documents many times, requiring all ports to conduct comprehensive disinfection of imported mail and goods. Hope to intercept contaminated items at the gate. When the port is killed, the express company will also kill it, but in reality, there are still cases of imported fruit and positive nucleic acid tests for international mail.
Zhang Liubo, chief expert of disinfection at the Chinese Center for Disease Control and Prevention, previously stated that the current international pandemic of the new crown epidemic is still ongoing, and mail and goods entering China may be contaminated by the new crown virus. Some viruses may gradually die during transit, but under certain conditions, some viruses do not die and the goods become infectious.
Zhang Liubo said, assuming that the amount of new coronavirus contaminated on foreign items is relatively large, and at the same time, if the transfer workers cough or sneeze, there may be more organic matter on the saliva and sputum. Better protection against viruses. Coupled with the fact that it is winter in the northern hemisphere now, the virus will survive for a lot longer. If it is transported by air and the time is short, there may be a risk of infection when we come into contact with these goods and these packaging surfaces.