Background: Initial cases of coronavirus disease 2019 (COVID-19) reported in Hong Kong were mostly imported cases from Mainland China. However, most cases reported in February 2020 were local infections with unknown source, indicating local community transmissions. This study aimed to report the clinical, epidemiological and phylogenomic characteristics of the local cases of COVID-19 in our community. Methods: We extracted the demographic, clinical and epidemiological data from 50 COVID-19 patients, who accounted for 53.8% of the cases in Hong Kong by the end of February 2020. We used both Nanopore and Illumina platforms to perform whole-genome sequencing (WGS) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from these patients. Phylogenetic relatedness among these local cases and their placement in the global phylogeny were examined. The evolutionary rate and divergence time of transmission were also determined. Findings: Of these 50 patients, only three (6.0%) had visited Wuhan while 43 (86.0%) did not have recent travel records. The average interval from symptom onset to hospital admission was 8.5 days. The most common signs and symptoms on admission were cough (74.0%) and fever (58.0%). Radiographic abnormality was found in 46 (92.0%) patients. Three (6.0%) patients required ICU admission. Phylogenetic analysis concurred with epidemiological investigation that 42 (84.0%) cases could be grouped into six transmission clusters. Forty-four (88.0%) cases harboured a common mutation Orf3a G251V. Global phylogeny of SARS-CoV-2 revealed that most (88.0%) cases in Hong Kong were clustered in two subclades with the strains from other countries. The estimated time to the most recent common ancestor (tMRCA) of COVID-2019 outbreak in Hong Kong was December 24, 2019 with an evolutionary rate of 3.04x10-3 substitutions per site per year. The reproduction number value was 1.84 as of February 28, 2020 in Hong Kong. Interpretation: We provided a territory-wide overview of COVID-19 in Hong Kong, which has borders connecting to Mainland China. Transmission in closed settings especially during family and religious gatherings is a hallmark of the recently reported cases. The reproduction number value indicated an ongoing outbreak in the community. Social distancing and vigilant epidemiological control are crucial to the containment of COVID-19 transmission

SARS-CoV-2 causes disease varying in severity from asymptomatic infections to severe respiratory distress and death in humans. The viral factors which determine transmissibility and pathogenicity are not yet clearly characterized. We used the hamster infection model to compare the replication ability and pathogenicity of five SARS-CoV-2 strains isolated from early cases originating in Wuhan, China, in February, and infected individuals returning from Europe and elsewhere in March 2020. The HK-13 and HK-95 isolates showed distinct pathogenicity in hamsters, with higher virus titers and more severe pathological changes in the lungs observed compared to other isolates. HK-95 contains a D614G substitution in the spike protein and demonstrated higher viral gene expression and transmission efficiency in hamsters. Intra-host diversity analysis revealed that further quasi species were generated during hamster infections, indicating that strain-specific adaptive mutants with advantages in replication and transmission will continue to arise and dominate subsequent waves of SARS-CoV-2 dissemination.

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Bacterial pathogens that cannot be identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) are occasionally encountered in clinical laboratories. The 16S rRNA gene is often used for sequence-based analysis to identify these bacterial species. Nevertheless, traditional Sanger sequencing is laborious, time-consuming and low-throughput. Here, we compared two commercially available 16S rRNA gene sequencing tests, which are based on Illumina and Nanopore sequencing technologies, respectively, in their ability to identify the species of 172 clinical isolates that failed to be identified by MALDI-TOF MS. Sequencing data were analyzed by respective built-in programs (MiSeq Reporter Software of Illumina and Epi2me of Nanopore) and BLAST+ (v2.11.0). Their agreement with Sanger sequencing on species-level identification was determined. Discrepancies were resolved by whole-genome sequencing. The diagnostic accuracy of each workflow was determined using the composite sequencing result as the reference standard. Despite the high base-calling accuracy of Illumina sequencing, we demonstrated that the Nanopore workflow had a higher taxonomic resolution at the species level. Using built-in analysis algorithms, the concordance of Sanger 16S with the Illumina and Nanopore workflows was 33.14% and 87.79%, respectively. The agreement was 65.70% and 83.14%, respectively, when BLAST+ was used for analysis. Compared with the reference standard, the diagnostic accuracy of Nanopore 16S was 96.36%, which was identical to Sanger 16S and was better than Illumina 16S (69.07%). The turnaround time of the Illumina workflow and the Nanopore workflow was 78h and 8.25h respectively. The per-sample cost of the Illumina and Nanopore workflows was US$28.5 and US$17.7, respectively.

Sensitive detection of Mycobacterium tuberculosis (TB) in small percentages in metagenomic samples is essential for microbial classification and drug resistance prediction. However, traditional methods, such as bacterial culture and microscopy, are time-consuming and sometimes have limited TB detection sensitivity. Oxford nanopore technologies (ONT) MinION sequencing allows rapid and simple sample preparation for sequencing. Its recently developed adaptive sequencing selects reads from targets while allowing real-time base-calling to achieve sequence enrichment or depletion during sequencing. Another common enrichment method is PCR amplification of the target TB genes. In this study, we compared both methods using ONT MinION sequencing for TB detection and variant calling in metagenomic samples using both simulation runs and those with synthetic and patient samples. We found that both methods effectively enrich TB reads from a high percentage of human (95%) and other microbial DNA. Adaptive sequencing with readfish and UNCALLDE achieved a 3.9-fold and 2.2-fold enrichment compared to the control run. We provide a simple automatic analysis framework to support the detection of TB for clinical use, openly available at https://github.com/HKU-BAL/ONT-TB-NF. Depending on the patient's medical condition and sample type, we recommend users evaluate and optimize their workflow for different clinical specimens to improve the detection limit.