Transmission dynamics, serial interval and epidemiology of COVID-19 diseases in Hong Kong under different control measures

Background: The outbreak of coronavirus disease 2019 (COVID-19) started in Wuhan, China in late December 2019, and subsequently became a pandemic. Hong Kong had implemented a series of control measures since January 2020, including enhanced surveillance, isolation and quarantine, border control and social distancing. Hong Kong recorded its first case on 23 January 2020, who was a visitor from Wuahn. We analysed the surveillance data of COVID-19 to understand the transmission dynamics and epidemiology in Hong Kong. Methods: Based on cases recorded from 23 January to 6 April 2020, we constructed the epidemic curve of daily COVID-19 incidence and used this data to estimate the time-varying reproduction number ( R t ) with the R package EpiEstim, with serial interval computed from local data. We described the demographic and epidemiological characteristics of reported cases. We computed weekly incidence by age and residential district to understand the spatial and temporal transmission of the disease. Results: COVID-19 disease in Hong Kong was characterised with local cases and clusters detected after two waves of importations, first in late January and the second one in early March. The R t increased to approximately 2 and approximately 1, respectively, following these importations; it decreased to below 1 afterwards, which coincided with the implementation, modification and intensification of different control measures. Compared to local cases, imported cases were younger (mean age: 52 years among local cases vs 35 years among imported cases), had a lower proportion of underlying disease (9% vs 5%) and severe outcome (13% vs 5%). Cases were recorded in all districts but the incidence was highest in those in the Hong Kong Island region. Conclusions: Stringent and sustained public health measures at population level could contain the COVID-19 disease at a relatively low level

Varicella vaccine dose depended effectiveness and waning among preschool children in Hong Kong.

In Hong Kong, universal varicella vaccination was introduced in July 2014 with a two-dose schedule but the vaccines had been available in the private market since 1996. With data from varicella notification and surveys on immunization coverage, we used the screening method to estimate dose-specific varicella vaccine effectiveness (VE) among preschool children in Hong Kong before universal vaccination. We estimated the VE of one- and two-dose varicella vaccination against all notified varicella as 69.4% (95% confidence interval (95% CI) 69.5-71.2) and 93.4% (95% CI 91.7-94.7), respectively. We found that VE did not decrease with time since receipt. Varicella vaccine was more effective against complications (85.4% [95% CI 48.8-95.8] for one dose and 100% [95% CI -Inf to 100] for two doses) and against hospital admission (75.2% [95% CI 53.4-86.8] for one dose and 93.1% [95% CI 47.1-99.1] for two doses). Lower protection of one-dose varicella vaccine resulted in breakthrough varicella. Under universal vaccination, second-dose varicella vaccine (given as combined measles, mumps, rubella and varicella vaccine) was first scheduled for children when they reach primary one (about 6 years of age) and was recently advanced to 18 months of age. Shortening the interval between the first dose and second dose of varicella vaccination should reduce breakthrough varicella and outbreaks in preschool

School Closure and Mitigation of Pandemic (H1N1) 2009, Hong Kong

In Hong Kong, kindergartens and primary schools were closed when local transmission of pandemic (H1N1) 2009 was identified. Secondary schools closed for summer vacation shortly afterwards. By fitting a model of reporting and transmission to case data, we estimated that transmission was reduced ≈25% when secondary schools closed

Human Streptococcus suis Outbreak, Sichuan, China

Streptococcus suis outbreak was associated with exposure to sick or dead pigs

The epidemiology of COVID-19 cases and the successful containment strategy in Hong Kong-January to May 2020

BACKGROUND: Hong Kong, a Special Administrative Region of China, recorded its first confirmed coronavirus disease 2019 (COVID-19) case on 23 January 2020. We reviewed the case epidemiology and the various public health measures implemented from January to May 2020. METHODS: The epidemiological and clinical characteristics of the cases recorded in different phases of the epidemic were described and compared, and the effectiveness of the public health measures implemented were reviewed using the changes in the daily number of confirmed cases and the interval from symptom onset to hospital admission. RESULTS: Between January and May 2020, 1084 confirmed COVID-19 cases were reported, about 70% of which had a history of travel during the incubation period. The case fatality ratio was 0.4%. The local epidemic progressed through four phases: (1) preparedness and imported infection from mainland China, (2) local transmission, (3) imported infection from overseas countries associated with local transmission, and (4) controlled imported infection with limited local transmission, with an eventual reduction of the daily case number and minimization of the onset-to-admission interval. Various public health measures, including enhanced surveillance, border control, and social distancing, were introduced in phases in response to the prevailing local and global situations. DISCUSSION: The overall containment strategy in Hong Kong led to a stabilization of the number of cases and the absence of a community-wide outbreak during the 4.5 m after the first case was reported. This strategy of containment might serve as an example for future planning of preparedness and response against novel infectious agents

Seasonal influenza vaccine effectiveness at primary care level, Hong Kong SAR, 2017/2018 winter

The 2017/18 winter influenza season in Hong Kong started in early January 2018, predominated by influenza B/Yamagata. We collaborated with private medical practitioners of our sentinel surveillance system to collect respiratory specimens and clinical information from patients with influenza-like illness for estimation of the influenza vaccine effectiveness (VE) using the test-negative case-control design. We found that the overall VE was 59.1% (95%CI 41.1 to 71.8%) against all influenza and 53.5% (95%CI 35.4 to 74.6%) against influenza B. Seasonal influenza vaccine provided moderate to good protection against laboratory-confirmed influenza infection at primary care level in Hong Kong in the 2017/18 winter influenza season

Clostridium difficile infection outbreak in a male rehabilitation ward, Hong Kong (China), 2011

Clostridium difficile is an anaerobic, gram-positive bacterium, capable of sporulation when environmental conditions no longer support its growth. The sporulation capacity enables the organism to persist in the environment for extended periods of time. Clostridium difficile is the main pathogen accountable for antibiotic-associated colitis and for 15% to 25% of cases of nosocomial antibiotic-associated diarrhoea. Major risk factors such as increased severity of underlying illness, increased age, prior antimicrobial use and gastric acid suppressors have been identified for Clostridium difficile

Mass measles immunization campaign: experience in the Hong Kong Special Administrative Region of China.

After the 1988 measles outbreak, annual notification rates for measles in Hong Kong SAR between 1989 and 1999 were 0.4-4.9 per 100 000, with peaks in 1992, 1994 and 1997. The first half-year incidence rates per 100 000 were 2.3 in 1997, 0.5 in 1995 and 1.2 in 1996. Monthly notification rates increased from a baseline of <10 cases to 59 in May 1997. Serological surveillance showed only 85.5% of children aged 1-19 years had measles antibodies. An epidemic, mainly because of failure of the first dose to produce immunity, seemed imminent in mid-1997. A mass immunization campaign targeted children aged 1-19 from July to November 1997. The overall coverage was 77%. The rate of adverse events was low. After the campaign, measles notification fell to 0.9 per 100 000 in 1998. A two-dose strategy and supplementary campaigns will maintain measles susceptibility at levels low enough to make measles elimination our goal