Half year into the pandemic: Hong Kong chapter

Dr. Thomas TsangController, Centre for Health Protection

October 17, 2009

Where are we now?

Laboratory confirmed cases(as of October 10, 2009)

• Cumulative: 30,225 • Dependent on testing policy

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ILI consultation rate among sentinel GPs

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Institutional ILI outbreaks

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Influenza-like illness outbreaks (流感樣爆發個案)

% +ve for HSI among tested DFC patients

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指定流感診所求診者對人類豬型流感測試呈陽性反應的百分比

HSI: dominant strain of influenza virus

Percentage of flu virus among all flu viruses detected

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HSI H3N2 H1N1 A (Not typed) B C

Age distribution & attack rate (May 1 – Oct 10)

67% : < 20 years old82% : < 30 years old

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HSI cases

Attack rate

Hospitalization and age (Jun 27 – Sep 27)

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Admitted Not admitted Percentage requiring hospitalisation

Overall percentage of cases requiring hospitalization: 13.9%

Severe & fatal HSI (as of October, 14)

• 142 severe HSI infections– 0.46% of total laboratory confirmed cases– 83 males; 59 females– Aged 13 months - 93 years (median: 51 years)– 75% had underlying diseases/risk factors– 66% required intensive care– Nucleotide sequencing closely similar to circulating HSI strain

• 32 fatal cases– 23 males; 9 females– Aged 11 years - 93 years (median: 55.5 years)– Case fatality ratio = 0.1%– 88% had underlying diseases/risk factors

ILI outbreaks (Sep 1 – Oct 9)

• 1,076 ILI outbreaks

• 1,017 (94.5%) in schools– 150 (13.9%) in kindergartens / child care centres– 441 (41.0%) in primary schools– 404 (37.5%) in secondary schools– 22 (2.0%) in special schools

• 51 advised to suspend classes

Antiviral resistance

• 3 sporadic cases in HK– One case associated with post-exposure prophylaxis– No onward transmission of drug-resistant viruses

• Global situation (as of Sep 27)– 28 oseltamivir-resistant HSI isolates– All show same H275Y mutation that confers

resistance to oseltamivir, but not to zanamivir– Worldwide, > 10,000 specimens of HSI virus have

been tested and found to be sensitive to oseltamivir

Containment phase measures

• Case isolation

• Contact management– Quarantine– Direct Observed Chemoprophylaxis– Medical surveillance

• Border health measures

• Surveillance, hygiene campaigns, etc.

Mitigation phase measures• Schools

– Early summer break for primary schools, kindergartens, etc.– Suspension of schools with large HSI outbreak

• Designated Fever Clinics

• Management of serious cases

• Antiviral stockpile deployment

• Vaccination

• Surveillance, self-care, hygiene campaigns, etc.

Case fatality (as of October 4, 2009)

WHO Region  

Cumulative total

Cases* Deaths

Africa 12,382 70

Americas 146,016 3,292

Eastern Mediterranean 12861 80

Europe > 59,000 > 193

South-East Asia 38,038 480

Western Pacific 109,926 410

Total > 378,223 > 4,525

1,462 deaths in 177,457 cases reported to WHO (August 13), crude case fatality rate = 0.82% (HK = 0.1%: intensive testing?)

Effect of community hygienic measures on respiratory viruses isolation (2003)

• Respiratory infections during SARS outbreak, Hong Kong, 2003 (Emerg Infect Dis. 2005 Nov;11(11):1738-41)– Effect of during SARS outbreak studied by comparing proportion of

+ve specimens of various respiratory viruses in 2003 with those from 1998 to 2002

– Community hygienic measures significantly reduced incidence of respiratory viral infections

Effect of school closure (2008 Easter, HK)

GOPCs (2008)*

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Sentinel GPs (2008)

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influenza isolates

Percentage

: school closure period

Influenza virus isolation at Public HealthLaboratory Centre

Sentinel ILI consultation rates (GOPCs/GPs)

What else from here?

‘In the 1918–1919 pandemic, 1st wave began in March 1918 and spread unevenly through United States, Europe, and possibly Asia over the next 6 months. Illness rates were high, but death rates in most locales were not appreciably above normal. A 2nd or fall wave spread globally from September to November 1918 and was highly fatal.’

Taubenberger JK, Morens DM. Emerg Infect Dis [serial on the Internet]. 2006 Jan [date cited]. Available from http://www.cdc.gov/ncidod/EID/vol12no01/05-0979.htm

“Asian Flu 1957”• May 1957: WHO received news of extensive influenza epidemics in

HK & Singapore

• Epidemics had begun at end of February in China

• In 6 months, every part of the world had experienced cases

• 1st wave: concentrated in school-aged children

• 2nd wave: followed disappearance of the first from 1 to 3 months later, causing very high rate of illness and increased fatalities and affected mostly elderly

• Estimated deaths > 2 millions

Avian influenza: assessing the pandemic threat. WHO. January 2005.

Mortality Distributions & Timing of Waves of Previous Pandemics

Miller MA, et al. N Engl J Med. 2009 May 7.

• More rapid population movement

• Higher prevalence of pre-existing medical conditions

• Medical advances, antibiotics, antivirals

What’s different in 21st century

Strategies• Surveillance

• Medical services

• Non-pharmacological measures– Hygiene, outbreak management,

social distancing, etc.

• Pharmacological measures– Antivirals– Vaccines

Seasonal flu & pneumococcal vaccination programs

• Government Vaccination Program

• Private doctors

– Childhood Influenza Vaccination Subsidy Scheme

– Elderly Vaccination Subsidy Scheme

Vaccination subsidy schemes• Government will subsidise:

– Elderly Vaccination Subsidy Scheme - eligible elders to receive influenza vaccine & pneumococcal vaccine from private doctors

– Childhood Influenza Vaccination Subsidy Scheme - children age between 6 months and less than 6 years to receive influenza vaccine from private doctors

Target groups for HSI vaccination

• Recommendations of Scientific Committees of CHP

– Healthcare workers

– Persons at higher risk of death and complications from HSI due to underlying medical conditions (including pregnancy)

– Children aged > 6 months and below 6 years old

– Elderly persons aged > 65

Patients with chronic diseases have much higher percentage of serious illnesses across all age groups

CategoriesNumber of severe cases#

Percentage of cases classified as ‘severe’ (%)

Number of fatal cases

Percentage of cases died (%)

<=5 years with chronic diseases 1 7.14% 0 0%

<=5 years without chronic diseases 2 0.12% 0 0%

6-11 years (primary school students) with chronic diseases 1 1.72% 0 0%

6-11 years (primary school students) without chronic diseases 1 0.05% 0 0%

12-18 years (secondary school students) with chronic diseases 1 1.45% 0 0%

12-18 years (secondary school students) without chronic diseases 2 0.07% 0 0%

19-64 years (adults) with chronic diseases 13 3.64% 3 0.84%

19-64 years (adults) without chronic diseases 31 0.53% 7 0.12%

>=65 years (elderly) with chronic diseases 13 15.48% 2 2.38%

>=65 years (elderly) without chronic diseases 1 1.85% 0 0%

#Information on chronic disease status is available in 12,795 cases out of the 14,363 cases

Elderly, young children, patients with chronic diseases have higher hospitalization rates

CategoriesTotal number of cases#

Percentage requiring hospitalization* (%)

<=5 years with chronic diseases 14 42.9%

<=5 years without chronic diseases 1,669 31.8%

6-11 years (primary school students) with chronic diseases 58 13.8%

6-11 years (primary school students) without chronic diseases 1,859 15.4%

12-18 years (secondary school students) with chronic diseases 69 24.6%

12-18 years (secondary school students) without chronic diseases 2,802 8.2%

19-64 years (adults) with chronic diseases 357 22.4%

19-64 years (adults) without chronic diseases 5,829 8.1%

>=65 years (elderly) with chronic diseases 84 60.7%

>=65 years (elderly) without chronic diseases 54 60.8%

#Information on chronic disease status is available in 12,795 cases out of the 14,363 cases*Calculation based on cases confirmed between 27 June and 7 September (in mitigation phase when only relatively serious cases require hospitalization)

Most severe cases occur in adults Elders and young children have highest rates of severe illness

Age groups

Number of cases classified as ‘severe’

Percentage of cases classified as ‘severe’ (%)

Reported severe cases / 100,000 population)

Number of fatal cases

Case fatality rate (%)

Deaths / 100,000 population

< 6 years 3 0.15% 1.10 0 0% 0

6-11 years (primary school students)

2 0.08% 0.58 0 0% 0

12-18 years (secondary school students)

3 0.09% 0.51 0 0% 0

19-64 years (adults) 44 0.66% 0.90 9 0.14% 0.18

65 years (elderly) 14 9.46% 1.55 3 2.03% 0.33

Young children have highest attack rates Young children and elders have highest hospitalization rates

Age groupsNumber of cases

Percentage of total cases (%)

Reported cases/100,000 population

Percentage of cases requiring hospitalization* (%)

< 6 years 1,961 13.7% 719.6 29.1%

6-11 years (primary school students)

2,359 16.4% 681.0 13.9%

12-18 years (secondary school students)

3,254 22.7% 554.6 8.0%

19-64 years (adults) 6,641 46.2% 135.5 9.0%

65 years (elderly) 148 1.0% 16.4 61.4%

Pregnant women have high percentage of hospitalization

CategoriesTotal number of cases

Percentage of all cases (%)

Percentage requiring hospitalization* (%)

Persons with chronic disease# 582 4.05% 27.8%

Pregnant women 97 0.68% 71.1%

HA staff 408 2.84% 3.0%

Age < 6 year without chronic illness 1,669 11.62% 31.8%

Age 65 years old without chronic illness 54 0.38% 60.8%

#Information on chronic disease status is available in 12,795 cases out of the 14,363 cases*Calculation based on cases confirmed between 27 June and 7 September (in mitigation phase when only relatively serious cases require hospitalization)

Background Incidence of GBS

Overseas Hong Kong

Background incidence (literature)

10-20 per million adults

<15 years 6 per millionOver 15 years 4.4 per million

HA data (2003-2008 Oct 15)

-

Total number during the period<15 years: 19 cases (2-7 per year)>=15 year: 279 cases (43-56 per year)

Average Incidence7.4 per million

AFP data (age<15y) -

2004: 2 cases (1.99 per million)2005: 8 cases (8.25 per million)2006: 3 cases (3.19 per million)2007: 2 cases (2.17 per million)2008: 1 case (1.11 per million)Average: 3.20 cases (3.34 per million)

After flu vaccination1-2 per million vaccinated

Not available

Summary

• Epidemiology of HSI in HK is in general agreement with global picture (low case fatality ratio real or artifact?)

• Recent data shows HSI probably peaked late September

• Timing and severity of ‘second wave’ uncertain

• School closures seemed to have delayed transmission, but outbreaks returned once school re-opened

• Local epidemiological data supports target groups for HSI vaccination, including persons with underlying medical conditions, young children, elders, HCW