key: cord-0802302-dlicb2ue authors: Lam, Ho Yeung; Lam, Tsz Sum; Wong, Chi Hong; Lam, Wing Hang; Leung, Chi Mei Emily; Au, Ka Wing Albert; Lam, Chau Kuen Yonnie; Lau, Tin Wai Winnie; Chan, Yung Wai Desmond; Wong, Ka Hing; Chuang, Shuk Kwan title: The Epidemiology of COVID-19 cases and the Successful Containment Strategy in Hong Kong – January to May 2020 date: 2020-06-21 journal: Int J Infect Dis DOI: 10.1016/j.ijid.2020.06.057 sha: a66e0e60c556b6402e66f450ac3a316a1e8af631 doc_id: 802302 cord_uid: dlicb2ue 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. METHOD: We described and compared the epidemiological and clinical characteristics of the cases recorded in different phases of the epidemic and reviewed the effectiveness of the public health measures implemented 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 travel history during the incubation period. The case fatality ratio was 0.4%. The local epidemic progressed through four phases: (i) preparedness and imported infection from mainland China, (ii) local transmission, (iii) imported infection from overseas countries associated with local transmission, and (iv) controlled imported infection with limited local transmission, with an eventual reduction of daily case number and minimization of 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: Hong Kong’s overall containment strategy has led to a stabilization of number of cases and absence of community-wide outbreak in the 4.5 months since the reporting of the first case. Hong Kong’s strategy of containment might serve as an example for future planning of preparedness and response against novel infectious agents. (iv) controlled imported infection with limited local transmission, with an eventual reduction of daily case number and minimization of 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. Hong Kong's overall containment strategy has led to a stabilization of number of cases and absence of community-wide outbreak in the 4.5 months since the reporting of the first case. Hong Kong's strategy of containment might serve as an example for future planning of preparedness and response against novel infectious agents. For each confirmed case, relevant epidemiological and clinical data collected from CHP's epidemiological investigations were extracted from CHP's electronic databases. Based on the travel history during the incubation period (IP, defined as 14 days before symptom onset) and CHP's epidemiological investigation, each confirmed case was classified as either - Imported case (travelled to a place with local COVID-19 transmission during IP)  Linked local case (no travel history during IP, with source identified)  Unlinked local case (no travel history during IP, with no source identified)  Possibly imported case (travel history during part of the IP) We described and compared the epidemiological and clinical profiles of the confirmed cases between different case classifications and phases of the epidemic, using appropriate statistical tests with Microsoft Excel 2013 and R version 3.6.0. The evolution of the COVID-19 epidemic in Hong Kong was described using epidemic curves. We reviewed the various major public health measures implemented by the Government in response to the prevailing disease situation 2 . Their overall effectiveness was assessed by calculating the 7-day moving J o u r n a l P r e -p r o o f averages of the daily number of confirmed cases reported and the interval from symptom onset to hospital admission (onset-to-admission interval) 3 . The latter gave an indication of the duration the case spent within the community while being infectious. For asymptomatic cases, the onset date was substituted by the collection date of the first positive specimen. For imported case, the date of arrival at Hong Kong would be used if it was later than the onset date, so as to allow a realistic assessment of the public health interventions. Descriptive and analytical epidemiology ( Table 1) A total of 1084 confirmed cases was reported between January and May 2020, comprising of 588 males and 496 females (M:F ratio: 1.19:1) aged from 40 days to 96 years (mean: 37.5; median: 35). The dates of symptom onset were between 18 January and 26 May 2020. Among the 859 patients (79.2%) who reported symptoms, the five most common symptoms included cough (436, 50.8%), fever (428, 49.8%), sore throat (174, 20.3%), headache (98, 11.4%) and runny nose (97, 11.3%). The remaining 225 cases (20.8%) were asymptomatic, with the first asymptomatic case reported on 23 February 2020. All cases were isolated in public hospitals. As at 31 May 2020, 1036 patients had been discharged with an average length of stay of 21.6 days (range: 1-94 days; median: 20 days). 4 deaths were reported involving 3 males and 1 female aged from 39 to 80 (case fatality ratio: 0.4%), all of which had underlying medical conditions such as diabetes and hypertension. Apart from the 4 fatal cases, 25 and 24 cases were ever in critical and serious condition respectively. Most of the cases remained in a stable condition (1031 cases). There was no significant difference in gender distribution between the 4 groups of case classification. Notably, more than 40% of imported cases were from the 15-24 age group compared with the other three groups, where cases from the 25-44 and 45-64 age groups predominated. About one-fourth of unlinked local cases had ever been in critical or serious conditions or deceased, which was higher than the other groups. Most imported cases were identified from enhanced surveillance for returning travellers and active notification by medical practitioners while most unlinked local cases were identified from enhanced surveillance in hospitals, GOPCs and private sector. Over half of the linked local cases were identified through contact tracing by CHP. Unlinked local cases had the longest average onset-to-admission interval (6.3 days) while imported cases had shorter average length of hospital stay than local cases (20.4 and 21.8 days versus 24.1 and 23.6 days). Phases of epidemic and public health measures ( Figure 1 and Table 2) The epidemic in Hong Kong progressed through four phases, from preparedness and imported infection from mainland China, local transmission, imported infection from overseas countries associated with local transmission to finally controlled imported infection with limited local transmission. The overall shape of the epidemic curve was characterised by a stable number of cases reported during the first two phases, followed by a surge in phase three and then an eventual drop in case numbers during phase four. J o u r n a l P r e -p r o o f The reporting criteria was updated from time to time based on the concurrent knowledge on COVID-19 and the evolving global situation. The clinical criteria which required the presence of both fever and respiratory symptoms was revised on 23 January 2020 to either one upon the findings of afebrile presentations in a number of cases. The epidemiological criteria, at first only including travel history to Wuhan, was later extended to cover the entire Hubei province. To detect cases without travel history to affected areas, COVID-19 testing for all inpatients admitted to public hospitals with pneumonia without travel history was introduced on 13 January 2020. Enhanced border control measures, including surveillance targeting inbound travellers from affected areas, suspension of passenger services at boundary control points, entry restriction and mandatory 14day quarantine for arriving passengers were implemented to limit the population flow to and from affected areas, initially including Wuhan and later the whole Hubei province. Various social distancing measures were also promulgated by the Government to reduce interpersonal contact in the community, including school suspension, cancellation of large-scale social events and work-from-home arrangements for civil servants. Meanwhile, multiple provinces in mainland China were reporting a marked increase in cases. Since mid-February, increases in cases was also reported globally with massive local transmission in some countries including South Korea 4 , Italy 5 and Iran 6 . In Hong Kong, the first unlinked local case was confirmed on 4 February, signifying entry into the next phase of the epidemic. The daily number of reported cases in this phase were between zero to 10. More than half of the cases recorded were linked local cases identified through contact tracing, with most of them belonging to clusters associated with social or religious gatherings around the Chinese New Year holidays at the end of January. Epidemiological investigation revealed that the transmission probably occurred during gatherings when the sources were pre-symptomatic or asymptomatic. Of note, the largest cluster involved 9 attendees and 3 workers of a Buddhist temple that further spread to 7 of their close contacts. The source was suspected to be an asymptomatic carrier who had previously travelled to mainland China. For imported cases, only two had travel history to mainland China, while the rest (9 cases) were evacuees from the Diamond Princess Cruise where a massive COVID-19 outbreak occurred 7 . The reporting criteria was further revised to include travel history to all areas with active community transmission. It was also noted that some cases had consulted their primary care physicians prior to admission but were not tested for COVID-19. They in general had a longer onset-to-admission interval. To increase the testing coverage and availability of testing in out-patient settings for early case detection, free COVID-19 testing was made available in GOPCs, emergency departments and later for private medical To allow earlier identification and isolation of imported cases, free COVID-19 testing service was provided for returning travellers at the airport, first on a voluntary basis and later became compulsory. This "hold and test" arrangement required them to wait at a holding centre for the test results. The overall effort of enhanced surveillance could be exemplified by the fact that it identified nearly half of the cases reported in this phase and the vastly increased number of COVID-19 tests performed daily, from 161 in phase one to 2283 in phase three. The worsening global situation led to additional border control measures, including the extension of the compulsory home quarantine requirement to returnees from all overseas countries, denial of entry for non-Hong Kong residents from overseas countries and the suspension of transit services at the airport. The occurrence of multiple local clusters involving bars and social gatherings called for intensification of social distancing measures. Apart from closure of additional governmental community venues, the Government also introduced regulations mandating closure of 11 types of premises including cinemas, fitness centres, karaokes and bars. A ban on gatherings of more than four people in a public place was also imposed. In addition, legal restrictions on restaurant operation was introduced to limit the mixing of patrons with enhanced infection control measures such as temperature screening. Phase Four -Controlled imported infection with limited local transmission (20 April to 31 May 2020) While the epidemic continued globally, the daily number of cases reported in Hong Kong returned to a low level during this phase, with some days reporting zero case. Nearly 90% of cases were imported, with more than 60% being returnees from Pakistan. 2 sporadic local family clusters involving 5 cases without any travel history during IP were identified during this phase. For each cluster, extensive contact tracing and source finding were conducted. This included the use of deep throat saliva testing for all tenants in the same residential building and social and workplace contacts. The sources of both clusters could not be identified, implying the presence of low level local transmission in the community. Additional measures were implemented to increase the coverage of COVID-19 testing. Private medical practitioners could directly request COVID-19 testing from CHP's laboratory and the number of specimen collection points were doubled. Workers at the airport and staff of elderly and disability homes were offered free COVID-19 testing. A majority of imported cases were identified through the "hold and test" arrangement at the airport, which prevented their transmission to the community. While the existing border control measures were continued, exemptions to the mandatory quarantine requirements were extended to cover additional groups of individuals with needs to travelling between mainland China and Hong Kong, e.g. business owners and legal practitioners. The total number of cases reported remained at a low level throughout phase one and two. There was a small increase of linked local cases during phase two, corresponding to the local clusters associated with gatherings during the Chinese New Year holidays and an outbreak related to a Buddhist temple. There was a surge in reported cases from the beginning of phase three. Although the main drivers of this surge were imported and possibly imported cases from overseas returnees, a marked increase in linked local cases was observed from the several large local clusters involving bars, karaokes and social gatherings. Increase in unlinked local cases was also observed, though in a smaller scale. After reaching the peak around early April, the number of cases across different case classifications experienced a gradual decrease towards phase four and remained at a low level comparable to that of phase one and two. Interval from symptom onset to hospital admission (Figure 3 ) The duration of interval from symptom onset to hospital admission experienced some fluctuations from phase one followed by a decrease towards the end of the phase two. At the start of phase three, an increase in the duration was again observed, followed by a continuous decrease of the interval towards phase four. The duration experienced some fluctuations at the later part of phase four, with the rises being attributed to the 2 unlinked local cases who, after symptom onset, had spent several days in the community before admission. 8 . In general, our cases had a slightly higher male to female ratio (1.19:1 versus 1.03:1) and were younger (more than two-third of cases were below 45). The latter could be explained by the high proportion of imported cases being students returning from overseas. Notably, our case cohort was characterized by a much lower case fatality ratio (0.4%) than those reported globally during the same period (6.1%) 9 . Multiple factors, including younger case population, robust public healthcare system and earlier diagnosis through high laboratory testing rate, might have contributed to this phenomenon. In other overseas countries, the first wave of COVID-19 case importation was usually followed by widespread community transmissions 10 . Given its high population density and intimate connections to mainland China and the rest of the world, Hong Kong was highly vulnerable to community-wide outbreak following importations from the start. However, a different pattern of contained COVID-19 epidemic, characterised by a high proportion of imported cases with the absence of community-wide transmission, had instead emerged. While several studies in China and Italy have identified the positive impact of public health intervention such as lockdown and social distancing in curtailing the community-wide outbreak 11, 12, 13, 14 , our findings suggested that the timely implementation of public health measures in response to the prevailing situations was able to establish this pattern of containment, without resorting to extreme measures like city-wide lockdown or stay-at-home regulations. In phase one, the preparatory work for the looming epidemic laid the legal framework and logistical groundwork for the subsequent public health actions. Although travel restriction had not been recommended by the WHO 15 , our findings suggested that the border control measures, comprised of entry restriction and mandatory quarantine, were able to limit the number of cases imported from affected areas. There were several limitations regarding our study. As a descriptive study, causal relationships between the public health measures and the epidemic trend could not be established. In addition, the contribution of the effect of individual measures could not be assessed. Some cases might not be captured by our surveillance system due to under-diagnosis of mild cases and asymptomatic individuals who never presented to the healthcare system. It was likely that asymptomatic cases with silent transmission existed before the first reporting on 22 February 2020 and might play a role in the transmission chain involving unlinked local cases. Lastly, community participation and cooperation also played an important role in the successful containment of the epidemic in Hong Kong. There was already a high level of disease awareness in the J o u r n a l P r e -p r o o f community since phase one. Many private organizations adopted work-from-home arrangement and announced postponement of public events and shutdown of venues like theme parks. The absence of community-wide transmission might also be explained by the high prevalence of voluntary facemask wearing in the community, which was almost universal according to a local survey 16 . We noted that all the large local clusters involved occasions where mask wearing was either not practised or practicable, for example during meal gatherings. Although universal community masking was not unanimously recommended by the WHO 17 and other health authorities, our experience in Hong Kong suggested it might limit disease transmission, especially when coupled with other public health interventions, such as personal and environmental hygiene measures 18 . Further studies on the effectiveness of universal masking during pandemic is warranted. To maintain the current success of containment amid an ever-evolving global COVID-19 pandemic, a balance will need to be struck between protection of health and minimization of economic and social disruption. All public health measures should be continuously evaluated against the prevailing local and global situations. Overall, Hong Kong's combination of public health measures were associated with a stabilization of case numbers and an absence of community-wide COVID-19 outbreak in the 4.5 months since the reporting of the first case. Our strategy of containment might serve as an example for future planning of preparedness and response against novel infectious agents. The authors have no conflicts of interest to disclose. This study did not receive any specific grant from funding agencies in the public, commercial, or notfor-profit sectors. J o u r n a l P r e -p r o o f Approval was not required. Centre for Health Protection, Department of Health, Hong Kong Special Administrative Region. Communicable Disease Surveillance Case Definitions The Government of the Hong Kong Special Administrative Region Evaluation of the Effectiveness of Surveillance and Containment Measures for the First 100 Patients with COVID-19 in Singapore Korean Society of Infectious Diseases, Korean Society of Pediatric Infectious Diseases Healthcare-associated Infection Control and Prevention, and Korea Centers for Disease Control and Prevention COVID-19 and Italy: what next? Lancet Ministry of Health and Medical Education, IR Iran. 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Advice on the use of masks in the context of COVID-19 COVID-19 epidemic: disentangling the re-emerging controversy about medical facemasks from an epidemiological perspective The authors would like to thank the staff members of the Centre for Health Protection for their wholehearted dedications and valuable contributions to the outbreak investigation and control of COVID-19, as well as the colleagues at Hospital Authority for their professional care of COVID-19 patients.J o u r n a l P r e -p r o o f