Epidemiological characteristics and quarantine assessment of imported international COVID-19 cases, March to December 2020, Chengdu, China.

International flights have accelerated the global spread of Coronavirus Disease 2019 (COVID-19). Determination of the optimal quarantine period for international travelers is crucial to prevent the local spread caused by imported COVID-19 cases. We performed a retrospective epidemiological study using 491 imported COVID-19 cases in Chengdu, China, to describe the characteristic of the cases and estimate the time from arrival to confirmation for international travelers using nonparametric survival methods. Among the 491 imported COVID-19 cases, 194 (39.5%) were asymptomatic infections. The mean age was 35.6 years (SD = 12.1 years) and 83.3% were men. The majority (74.1%) were screened positive for SARS-CoV-2, conducted by Chengdu Customs District, the People's Republic of China. Asymptomatic cases were younger than presymptomatic or symptomatic cases (P < 0.01). The daily number of imported COVID-19 cases displayed jagged changes. 95% of COVID-19 cases were confirmed by PT-PCR within 14 days (95% CI 13-15) after arriving in Chengdu. A 14-day quarantine measure can ensure non-infection among international travelers with a 95% probability. Policymakers may consider an extension of the quarantine period to minimize the negative consequences of the COVID-19 confinement and prevent the international spread of COVID-19. Nevertheless, the government should consider the balance between COVID-19 and socioeconomic development, which may cause more serious social and health crises.

Characterization of a Programmable Argonaute Nuclease from the Mesophilic Bacterium Rummeliibacillus suwonensis.

Prokaryotic Argonautes (pAgos) from mesophilic bacteria are attracting increasing attention for their genome editing potential. So far, it has been reported that KmAgo from Kurthia massiliensis can utilize DNA and RNA guide of any sequence to effectively cleave DNA and RNA targets. Here we find that three active pAgos, which have about 50% sequence identity with KmAgo, possess typical DNA-guided DNA target cleavage ability. Among them, RsuAgo from Rummeliibacillus suwonensis is mainly explored for which can cleave both DNA and RNA targets. Interestingly, RsuAgo-mediated RNA target cleavage occurs only with short guide DNAs in a narrow length range (16-20 nt), and mismatches between the guide and target sequence greatly affect the efficiency of RNA target cleavage. RsuAgo-mediated target cleavage shows a preference for a guide strand with a 5'-terminal A residue. Furthermore, we have found that RsuAgo can cleave double-stranded DNA in a low-salt buffer at 37 °C. These properties of RsuAgo provide a new tool for DNA and RNA manipulation at moderate temperatures.