Effectiveness of mRNA and inactivated COVID-19 vaccines: A test-negative study in an infection-naïve Hong Kong population.

OBJECTIVE: Assess real-world effectiveness of vaccines against COVID-19. METHODS: A test-negative study was conducted in January-May 2022 during an Omicron BA.2 wave in Hong Kong. COVID-19 was identified by RT-PCR. 1-1 case-control matching was based on propensity score with vaccine effectiveness adjusted for confounders. RESULTS: Altogether, 1781 cases and 1737 controls aged 3-105 years were analysed. The mean lag time from the last dose of vaccination to testing for SARS-CoV-2 was 133.9 (SD: 84.4) days. Two doses of either vaccine within 180 days offered a low effectiveness against COVID-19 of all severity combined (VEadj [95% CI] for BNT162b2: 27.0% [4.2-44.5], CoronaVac: 22.9% [1.3-39.7]), and further decreased after 180 days. Two doses of CoronaVac were poorly protective 39.5% [4.9-62.5] against severe diseases for age ≥ 60 years, but the effectiveness increased substantially after the third dose (79.1% [25.7-96.7]). Two doses of BNT162b2 protected age ≥ 60 years against severe diseases (79.3% [47.2, 93.9]); however, the uptake was not high enough to assess three doses. CONCLUSIONS: The current real-world analysis indicates a high vaccine effectiveness of three doses of inactivated virus (CoronaVac) vaccines against Omicron variant, whereas the effectiveness of two doses is suboptimal.

Mucosal Antibody Response to SARS-CoV-2 in Paediatric and Adult Patients: A Longitudinal Study.

BACKGROUND: SARS-CoV-2 enters the body through inhalation or self-inoculation to mucosal surfaces. The kinetics of the ocular and nasal mucosal-specific-immunoglobulin A(IgA) responses remain under-studied. METHODS: Conjunctival fluid (CF, n = 140) and nasal epithelial lining fluid (NELF, n = 424) obtained by paper strips and plasma (n = 153) were collected longitudinally from SARS-CoV-2 paediatric (n = 34) and adult (n = 47) patients. The SARS-CoV-2 spike protein 1(S1)-specific mucosal antibody levels in COVID-19 patients, from hospital admission to six months post-diagnosis, were assessed. RESULTS: The mucosal antibody was IgA-predominant. In the NELF of asymptomatic paediatric patients, S1-specific IgA was induced as early as the first four days post-diagnosis. Their plasma S1-specific IgG levels were higher than in symptomatic patients in the second week after diagnosis. The IgA and IgG levels correlated positively with the surrogate neutralization readout. The detectable NELF "receptor-blocking" S1-specific IgA in the first week after diagnosis correlated with a rapid decline in viral load. CONCLUSIONS: Early and intense nasal S1-specific IgA levels link to a rapid decrease in viral load. Our results provide insights into the role of mucosal immunity in SARS-CoV-2 exposure and protection. There may be a role of NELF IgA in the screening and diagnosis of SARS-CoV-2 infection.

Cross-Clade Memory Immunity in Adults Following SARS-CoV-1 Infection in 2003.

Importance: Knowledge of the longevity and breath of immune response to coronavirus infection is crucial for the development of next-generation vaccines to control the COVID-19 pandemic. Objectives: To determine the profile of SARS-CoV-2 antibodies among persons infected with the closely related virus, SARS-CoV-1, in 2003 (SARS03 survivors) and to characterize their antibody response soon after the first and second doses of COVID-19 vaccines. Design, Setting, and Participants: This prospective cohort study examined SARS-CoV-2 antibodies among SARS03 survivors compared with sex- and age-matched infection-naive controls. Participants received the COVID-19 vaccines between March 1 and September 30, 2021. Interventions: One of the 2 COVID-19 vaccines (inactivated [CoronaVac] or messenger RNA [BNT162b2]) available in Hong Kong. Two doses were given according to the recommended schedule. The vaccine type administered was known to both participants and observers. Main Outcomes and Measures: SARS-CoV-2 antibodies were measured prevaccination, 7 days after the first dose, and 14 days after the second dose. Results: Eighteen SARS03 adult survivors (15 women and 3 men; median age, 46.5 [IQR, 40.0-54.3] years) underwent prevaccination serologic examination. The vast majority retained a detectable level of antibodies that cross-reacted with SARS-CoV-2 (16 of 18 [88.9%] with nucleocapsid protein antibodies and 17 of 18 [94.4%] with receptor-binding domain of spike protein antibodies); a substantial proportion (11 of 18 [61.1%]) had detectable cross-neutralizing antibodies. Twelve SARS03 adult survivors (10 women and 2 men) underwent postvaccination serologic examination. At 7 days after the first dose of vaccine, SARS03 survivors mounted significantly higher levels of neutralizing antibodies compared with controls (median inhibition: 89.5% [IQR, 77.1%-93.7%] vs 13.9% [IQR, 11.8%-16.1%] for BNT162b2; 64.9% [IQR, 60.8%-69.5%] vs 13.4% [IQR, 9.5%-16.8%] for CoronaVac; P < .001 for both). At 14 days after the second dose, SARS03 survivors generated a broader antibody response with significantly higher levels of neutralizing antibodies against variants of concern compared with controls (eg, median inhibition against Omicron variant, 52.1% [IQR, 35.8%-66.0%] vs 14.7% [IQR, 2.5%-20.7%]; P < .001). Conclusions and Relevance: The findings of this prospective cohort study suggest that infection with SARS-CoV-1 was associated with detectable levels of antibodies that cross-react and cross-neutralize SARS-CoV-2, which belongs to a distinct clade under the same subgenus Sarbecovirus. These findings support the development of broadly protective vaccines to cover sarbecoviruses that caused 2 devastating zoonotic outbreaks in humans over the last 2 decades.

Limited Impact of SARS-CoV-2 on the Human Naso-Oropharyngeal Microbiota in Hospitalized Patients.

Numerous studies have reported dysbiosis in the naso- and/or oro-pharyngeal microbiota of COVID-19 patients compared with healthy individuals; however, only a few small-scale studies have also included a disease control group. In this study, we characterized and compared the bacterial communities of pooled nasopharyngeal and throat swabs from hospitalized COVID-19 patients (n = 76), hospitalized non-COVID-19 patients with respiratory symptoms or related illnesses (n = 69), and local community controls (n = 76) using 16S rRNA gene V3-V4 amplicon sequencing. None of the subjects received antimicrobial therapy within 2 weeks prior to sample collection. Both COVID-19 and non-COVID-19 hospitalized patients differed in the composition, alpha and beta diversity, and metabolic potential of the naso-oropharyngeal microbiota compared with local controls. However, the microbial communities in the two hospitalized patient groups did not differ significantly from each other. Differential abundance analysis revealed the enrichment of nine bacterial genera in the COVID-19 patients compared with local controls; however, six of them were also enriched in the non-COVID-19 patients. Bacterial genera uniquely enriched in the COVID-19 patients included Alloprevotella and Solobacterium. In contrast, Mogibacterium and Lactococcus were dramatically decreased in COVID-19 patients only. Association analysis revealed that Alloprevotella in COVID-19 patients was positively correlated with the level of the inflammation biomarker C-reactive protein. Our findings reveal a limited impact of SARS-CoV-2 on the naso-oropharyngeal microbiota in hospitalized patients and suggest that Alloprevotella and Solobacterium are more specific biomarkers for COVID-19 detection. IMPORTANCE Our results showed that while both COVID-19 and non-COVID-19 hospitalized patients differed in the composition, alpha and beta diversity, and metabolic potential of the naso-oropharyngeal microbiota compared with local controls, the microbial communities in the two hospitalized patient groups did not differ significantly from each other, indicating a limited impact of SARS-CoV-2 on the naso-oropharyngeal microbiota in hospitalized patients. Besides, we identified Alloprevotella and Solobacterium as bacterial genera uniquely enriched in COVID-19 patients, which may serve as more specific biomarkers for COVID-19 detection.

Longitudinal Cytokine Profile in Patients With Mild to Critical COVID-19.

The cytokine release syndrome has been proposed as the driver of inflammation in coronavirus disease 2019 (COVID-19). However, studies on longitudinal cytokine profiles in patients across the whole severity spectrum of COVID-19 are lacking. In this prospective observational study on adult COVID-19 patients admitted to two Hong Kong public hospitals, cytokine profiling was performed on blood samples taken during early phase (within 7 days of symptom onset) and late phase (8 to 12 days of symptom onset). The primary objective was to evaluate the difference in early and late cytokine profiles among patient groups with different disease severity. The secondary objective was to assess the associations between cytokines and clinical endpoints in critically ill patients. A total of 40 adult patients (mild = 8, moderate = 15, severe/critical = 17) hospitalized with COVID-19 were included in this study. We found 22 cytokines which were correlated with disease severity, as proinflammatory Th1-related cytokines (interleukin (IL)-18, interferon-induced protein-10 (IP-10), monokine-induced by gamma interferon (MIG), and IL-10) and ARDS-associated cytokines (IL-6, monocyte chemoattractant protein-1 (MCP-1), interleukin-1 receptor antagonist (IL-1RA), and IL-8) were progressively elevated with increasing disease severity. Furthermore, 11 cytokines were consistently different in both early and late phases, including seven (growth-regulated oncogene-alpha (GRO-α), IL-1RA, IL-6, IL-8, IL-10, IP-10, and MIG) that increased and four (FGF-2, IL-5, macrophage-derived chemokine (MDC), and MIP-1α) that decreased from mild to severe/critical patients. IL-8, followed by IP-10 and MDC were the best performing early biomarkers to predict disease severity. Among critically ill patients, MCP-1 predicted the duration of mechanical ventilation, highest norepinephrine dose administered, and length of intensive care stay.

Seroprevalence of Unidentified SARS-CoV-2 Infection in Hong Kong During 3 Pandemic Waves.

Importance: Seroprevalence studies inform the extent of infection and assist evaluation of mitigation strategies for the COVID-19 pandemic. Objective: To estimate the prevalence of unidentified SARS-CoV-2 infection in the general population of Hong Kong. Design, Setting, and Participants: A prospective cross-sectional study was conducted in Hong Kong after each major wave of the COVID-19 pandemic (April 21 to July 7, 2020; September 29 to November 23, 2020; and January 15 to April 18, 2021). Adults (age ≥18 years) who had not been diagnosed with COVID-19 were recruited during each period, and their sociodemographic information, symptoms, travel, contact, quarantine, and COVID-19 testing history were collected. Main Outcomes and Measures: The main outcome was prevalence of SARS-CoV-2 infection. SARS-CoV-2 IgG antibodies were detected by an enzyme-linked immunosorbent assay based on spike (S1/S2) protein, followed by confirmation with a commercial electrochemiluminescence immunoassay based on the receptor binding domain of spike protein. Results: The study enrolled 4198 participants (2539 [60%] female; median age, 50 years [IQR, 25 years]), including 903 (22%), 1046 (25%), and 2249 (53%) during April 21 to July 7, 2020; during September 29 to November 23, 2020; and during January 15 to April 18, 2021, respectively. The numbers of participants aged 18 to 39 years, 40 to 59 years, and 60 years or older were 1328 (32%), 1645 (39%), and 1225 (29%), respectively. Among the participants, 2444 (58%) stayed in Hong Kong since November 2019 and 2094 (50%) had negative SARS-CoV-2 RNA test results. Only 170 (4%) reported ever having contact with individuals with confirmed cases, and 5% had been isolated or quarantined. Most (2803 [67%]) did not recall any illnesses, whereas 737 (18%), 212 (5%), and 385 (9%) had experienced respiratory symptoms, gastrointestinal symptoms, or both, respectively, before testing. Six participants were confirmed to be positive for anti-SARS-CoV-2 IgG; the adjusted prevalence of unidentified infection was 0.15% (95% CI, 0.06%-0.32%). Extrapolating these findings to the whole population, there were fewer than 1.9 unidentified infections for every recorded confirmed case. The overall prevalence of SARS-CoV-2 infection in Hong Kong before the roll out of vaccination was less than 0.45%. Conclusions and Relevance: In this cross-sectional study of participants from the general public in Hong Kong, the prevalence of unidentified SARS-CoV-2 infection was low after 3 major waves of the pandemic, suggesting the success of the pandemic mitigation by stringent isolation and quarantine policies even without complete city lockdown. More than 99.5% of the general population of Hong Kong remain naive to SARS-CoV-2, highlighting the urgent need to achieve high vaccine coverage.

Temporal-Geographical Dispersion of SARS-CoV-2 Spike Glycoprotein Variant Lineages and Their Functional Prediction Using in Silico Approach.

SARS-CoV-2 is a positive-sense single-stranded RNA virus with emerging mutations, especially on the Spike glycoprotein (S protein). To delineate the genomic diversity in association with geographic dispersion of SARS-CoV-2 variant lineages, we collected 939,591 complete S protein sequences deposited in the Global Initiative on Sharing All Influenza Data (GISAID) from December 2019 to April 2021. An exponential emergence of S protein variants was observed since October 2020 when the four major variants of concern (VOCs), namely, alpha (α) (B.1.1.7), beta (ß) (B.1.351), gamma (γ) (P.1), and delta (δ) (B.1.617), started to circulate in various communities. We found that residues 452, 477, 484, and 501, the 4 key amino acids located in the hACE2 binding domain of S protein, were under positive selection. Through in silico protein structure prediction and immunoinformatics tools, we discovered D614G is the key determinant to S protein conformational change, while variations of N439K, T478I, E484K, and N501Y in S1-RBD also had an impact on S protein binding affinity to hACE2 and antigenicity. Finally, we predicted that the yet-to-be-identified hypothetical N439S, T478S, and N501K mutations could confer an even greater binding affinity to hACE2 and evade host immune surveillance more efficiently than the respective native variants. This study documented the evolution of SARS-CoV-2 S protein over the first 16 months of the pandemic and identified several key amino acid changes that are predicted to confer a substantial impact on transmission and immunological recognition. These findings convey crucial information to sequence-based surveillance programs and the design of next-generation vaccines. IMPORTANCE Our study showed the global distribution of SARS-CoV-2 S protein variants from January 2020 to the end of April 2021. We highlighted the key amino acids of S protein subjected to positive selection. Using computer-aided approaches, we predicted the impact of the amino acid variations in S protein on viral infectivity and antigenicity. We also predicted the potential amino acid mutations that could arise in favor of SARS-CoV-2 virulence. These findings are vital for vaccine designing and anti-SARS-CoV-2 drug discovery in an effort to combat COVID-19.

Temporal landscape of human gut RNA and DNA virome in SARS-CoV-2 infection and severity.

BACKGROUND: Coronavirus disease 2019 (COVID-19) caused by the enveloped RNA virus SARS-CoV-2 primarily affects the respiratory and gastrointestinal tracts. SARS-CoV-2 was isolated from fecal samples, and active viral replication was reported in human intestinal cells. The human gut also harbors an enormous amount of resident viruses (collectively known as the virome) that play a role in regulating host immunity and disease pathophysiology. Understanding gut virome perturbation that underlies SARS-CoV-2 infection and severity is an unmet need. METHODS: We enrolled 98 COVID-19 patients with varying disease severity (3 asymptomatic, 53 mild, 34 moderate, 5 severe, 3 critical) and 78 non-COVID-19 controls matched for gender and co-morbidities. All subjects had fecal specimens sampled at inclusion. Blood specimens were collected for COVID-19 patients at admission to test for inflammatory markers and white cell counts. Among COVID-19 cases, 37 (38%) patients had serial fecal samples collected 2 to 3 times per week from time of hospitalization until after discharge. Using shotgun metagenomics sequencing, we sequenced and profiled the fecal RNA and DNA virome. We investigated alterations and longitudinal dynamics of the gut virome in association with disease severity and blood parameters. RESULTS: Patients with COVID-19 showed underrepresentation of Pepper mild mottle virus (RNA virus) and multiple bacteriophage lineages (DNA viruses) and enrichment of environment-derived eukaryotic DNA viruses in fecal samples, compared to non-COVID-19 subjects. Such gut virome alterations persisted up to 30 days after disease resolution. Fecal virome in SARS-CoV-2 infection harbored more stress-, inflammation-, and virulence-associated gene encoding capacities including those pertaining to bacteriophage integration, DNA repair, and metabolism and virulence associated with their bacterial host. Baseline fecal abundance of 10 virus species (1 RNA virus, pepper chlorotic spot virus, and 9 DNA virus species) inversely correlated with disease COVID-19 severity. These viruses inversely correlated with blood levels of pro-inflammatory proteins, white cells, and neutrophils. Among the 10 COVID-19 severity-associated DNA virus species, 4 showed inverse correlation with age; 5 showed persistent lower abundance both during disease course and after disease resolution relative to non-COVID-19 subjects. CONCLUSIONS: Both enteric RNA and DNA virome in COVID-19 patients were different from non-COVID-19 subjects, which persisted after disease resolution of COVID-19. Gut virome may calibrate host immunity and regulate severity to SARS-CoV-2 infection. Our observation that gut viruses inversely correlated with both severity of COVID-19 and host age may partly explain that older subjects are prone to severe and worse COVID-19 outcomes. Altogether, our data highlight the importance of human gut virome in severity and potentially therapeutics of COVID-19. Video Abstract.

A global analysis of replacement of genetic variants of SARS-CoV-2 in association with containment capacity and changes in disease severity.

OBJECTIVES: To examine severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant replacement in association with containment capacity and changes in case fatality at country level. METHODS: Altogether, 69 571 full SARS-CoV-2 genomes collected globally within the first 6 months of the pandemic were examined. The correlation between variant replacement and containment capacity was examined by logistic regression models using the WHO International Health Regulation (IHR) score, the Oxford COVID-19 Government Response Tracker (OxCGRT) and the vulnerability index INFORM as proxies, while correlation with changes in monthly crude case fatality ratios was examined by a mixed effect model. RESULTS: At the global level, variant lineage G∗, characterized by the S-D614G mutation, replaced the older lineages L and S in March 2020. European countries-including Finland, France and Italy-were the first to reach a 50% increment of G∗, whereas only Singapore and South Korea had non-G∗ persisting throughout the first 6 months. Countries with higher IHR scores (ß-coefficient -0.001, 95%CI -0.016, -0.001; p 0.034) and higher stringency indexes (OxCGRT) (ß-coefficient -0.011, 95%CI -0.020, -0.001; p 0.035) were associated with lower levels of G∗ replacement, whereas higher vulnerability indexes (INFORM) (ß-coefficient 0.049, 95%CI 0.001, 0.097; p 0.044) were associated with higher replacement levels. Crude case fatality ratio showed a positive correlation with G∗ replacement (ß-coefficient: 0.034, 95%CI 0.011, 0.058; p 0.004), even after adjusting for testing capacity and other country-specific characteristics. CONCLUSIONS: SARS-CoV-2 variant lineage G∗ (S-D614G) replaced older lineages more efficiently in countries with lower containment capacity, and its possible association with increased disease severity deserves further investigation.

Acceptance of the COVID-19 vaccine based on the health belief model: A population-based survey in Hong Kong.

BACKGROUND: Vaccines for COVID-19 are anticipated to be available by 2021. Vaccine uptake rate is a crucial determinant for herd immunity. We examined factors associated with acceptance of vaccine based on (1). constructs of the Health Belief Model (HBM), (2). trust in the healthcare system, new vaccine platforms and manufacturers, and (3). self-reported health outcomes. METHODS: A population-based, random telephone survey was performed during the peak of the third wave of COVID-19 outbreak (27/07/2020 to 27/08/2020) in Hong Kong. All adults aged ≥ 18 years were eligible. The survey included sociodemographic details; self-report health conditions; trust scales; and self-reported health outcomes. Multivariable regression analyses were applied to examine independent associations. The primary outcome is the acceptance of the COVID-19 vaccine. RESULTS: We conducted 1200 successful telephone interviews (response rate 55%). The overall vaccine acceptance rate after adjustment for population distribution was 37.2% (95% C.I. 34.5-39.9%). The projected acceptance rates exhibited a "J-shaped" pattern with age, with higher rates among young adults (18-24 years), then increased linearly with age. Multivariable regression analyses revealed that perceived severity, perceived benefits of the vaccine, cues to action, self-reported health outcomes, and trust in healthcare system or vaccine manufacturers were positive correlates of acceptance; whilst perceived access barriers and harm were negative correlates. Remarkably, perceived susceptibility to infection carried no significant association, whereas recommendation from Government (aOR = 10.2, 95% C.I. 6.54 to 15.9, p < 0.001) was as the strongest driving factor for acceptance. Other key obstacles of acceptance included lack of confidence on newer vaccine platforms (43.4%) and manufacturers without track record (52.2%), which are of particular relevance to the current context. CONCLUSIONS: Governmental recommendation is an important driver, whereas perceived susceptibility is not associated with acceptance of COVID-19 vaccine. These HBM constructs and independent predictors inform evidence-based formulation and implementation of vaccination strategies.

Prospective Study Comparing Deep Throat Saliva With Other Respiratory Tract Specimens in the Diagnosis of Novel Coronavirus Disease 2019.

BACKGROUND: Self-collected specimens have been advocated to avoid infectious exposure to healthcare workers. Self-induced sputum in those with a productive cough and saliva in those without a productive cough have been proposed, but sensitivity remains uncertain. METHODS: We performed a prospective study in 2 regional hospitals in Hong Kong. RESULTS: We prospectively examined 563 serial samples collected during the virus shedding periods of 50 patients: 150 deep throat saliva (DTS), 309 pooled-nasopharyngeal (NP) and throat swabs, and 104 sputum. Deep throat saliva had the lowest overall reverse-transcriptase polymerase chain reaction (RT-PCR)-positive rate (68.7% vs 89.4% [sputum] and 80.9% [pooled NP and throat swabs]) and the lowest viral ribonucleic acid (RNA) concentration (mean log copy/mL 3.54 vs 5.03 [sputum] and 4.63 [pooled NP and throat swabs]). Analyses with respect to time from symptom onset and severity also revealed similar results. Virus yields of DTS correlated with that of sputum (Pearson correlation index 0.76; 95% confidence interval, 0.62-0.86). We estimated that the overall false-negative rate of DTS could be as high as 31.3% and increased 2.7 times among patients without sputum. CONCLUSIONS: Deep throat saliva produced the lowest viral RNA concentration and RT-PCR-positive rate compared with conventional respiratory specimens in all phases of illness. Self-collected sputum should be the choice for patients with sputum.

Stringent containment measures without complete city lockdown to achieve low incidence and mortality across two waves of COVID-19 in Hong Kong.

INTRODUCTION: An international city, Hong Kong, in proximity to the first epicentre of COVID- 19, experienced two epidemic waves with different importation pressure. We compared the epidemiological features of patients with COVID-19 in the context of containment policies between the first and second waves. METHODS: We retrieved information on the first 1038 cases detected in Hong Kong (23 January to 25 April 2020) to analyse the epidemiological characteristics including age/gender-specific incidence, clustering, reproduction number (Rt ) and containment delay; in relation to the containment measures implemented. Factors associated with containment delay were evaluated by multiple linear regression analysis with age, gender, epidemic wave and infection source as covariates. A time series of 5-day moving average was plotted to examine the changes across the two epidemic waves. RESULTS: The incidence and mortality (135.5 and 0.5 per 1 000 000 population) was among the lowest in the world. Aggressive escalation of border control correlated with reductions in Rt from 1.35 to 0.57 and 0.92 to 0.18, and aversions of 450 and 1650 local infections during the first and second waves, respectively. Implementing COVID-19 tests for overseas returners correlated with an upsurge of asymptomatic case detection, and shortened containment delay in the second wave. Medium-sized cluster events in the first wave were family gatherings, whereas those in the second wave were leisure activities among youngsters. Containment delay was associated with older age (adjusted OR (AOR)=1.01, 95% CI 1.00 to 1.02, p=0.040), male gender (AOR=1.41, 95% CI 1.02 to 1.96, p=0.039) and local cases (AOR=11.18, 95% CI 7.43 to 16.83, p<0.001), and with significant improvement in the second wave compared with the first wave (average: 6.8 vs 3.7 days). A higher incidence rate was observed for males, raising possibility of gender predilection in susceptibility of developing symptoms. CONCLUSION: Prompt and stringent all-round containment strategies represent successful measures in pandemic control. These findings could inform formulation and implementation of pandemic mitigation strategies.

Epidemiological characteristics of the first 100 cases of coronavirus disease 2019 (COVID-19) in Hong Kong Special Administrative Region, China, a city with a stringent containment policy.

BACKGROUND: Hong Kong (HK) is a densely populated city near the epicentre of the coronavirus disease 2019 (COVID-19) outbreak. Stringent border control together with aggressive case finding, contact tracing, social distancing and quarantine measures were implemented to halt the importation and spread of the virus. METHODS: We performed an epidemiological study using government information covering the first 100 confirmed cases to examine the epidemic curve, incidence, clusters, reproduction number (Rt), incubation period and time to containment. RESULTS: A total of 93 of the 100 cases were HK residents (6 infected in Mainland China, 10 on the Diamond Princess Cruise). Seven were visitors infected in Mainland China before entering HK. The majority (76%) were aged ≥45 years, and the incidence increased with age (P < 0.001). Escalation of border control measures correlated with a decrease in the proportion (62.5% to 0%) of cases imported from Mainland China, and a reduction in Rt (1.07 to 0.75). The median incubation period was 4.2 days [95% confidence interval (CI), 4.0-4.5; 5th and 95th percentiles: 1.3 and 14.0). Most clusters with identifiable epidemiological links were households involving 2-4 people. Three medium-spreading events were identified: two from New Year gatherings (6-11 people), and another from environmental contamination of a worship hall (12 people). Despite intensified contact tracing, containment was delayed in 78.9% of cases (mean = 5.96 days, range = 0-24 days). An unusual transmission in a multi-storey building via faulty toilet plumbing was suspected with >100 residents evacuated overnight. Our analysis indicated that faulty plumbing was unlikely to be the source of this transmission. CONCLUSION: Timely stringent containment policies minimized the importation and transmission of COVID-19 in HK.

SARS-CoV-2 RNA Detection on Disposable Wooden Chopsticks, Hong Kong.

We detected severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA on disposable wooden chopsticks used by 5 consecutive asymptomatic and postsymptomatic patients admitted for isolation and care at our hospital. Although we did not assess virus viability, our findings may suggest potential for transmission through shared eating utensils.