INFLUENZA DISEASE BURDEN IN HONG KONG

Study 1 Influenza-related hospitalizations among children in Hong Kong –Chiu SS, Lau YL, Chan KH, Wong WH, Peiris JS –N Engl J Med 2002; 347: 2097–103

Study 1 Study design –Retrospective population-based study Target population –Children under 15 years old Study period –1997–1999 Method –Hospitalisation data from a regional general hospital from 1997 to 1999 were analysed to define influenza predominant and baseline periods –Admission for acute respiratory diseases to the hospital was correlated with influenza activity and extrapolated to the population of children in Hong Kong

Rates of excess hospitalisation for acute respiratory diseases attributable to influenza according to age group Adjusted mean annual rate/10,000 (95% CI) ___________________________________________________________ < 1 year278.5 (57.3–499.6)288.2 (191.6–386.4) 1 to < 2 years218.4 (95.6–354.9)209.3 (144.9–270.5) 2 to < 5 years125.6 (49.1–199.3)77.3 (45.1–107.9) 5 to < 10 years57.3 (30.0–84.6)20.9 (14.5–30.6) 10 to 15 years16.4 (10.9–21.8)8.1 (4.8–9.7) Study 1: major findings

Study 1: conclusions In the subtropics, influenza is an important cause of hospitalisation among children, with rates exceeding those reported for temperate regions. Wider use of influenza vaccine for children should be considered More studies on other subtropical countries are needed

Study 2 Excess hospital admissions for pneumonia, chronic obstructive pulmonary disease, and heart failure during influenza seasons in Hong Kong. –Yap FH, Ho PL, Lam KF, Chan PK, Cheng YH, Peiris JS –J Med Virol 2004; 73: 617–23

Study 2 Study design –Retrospective Target population –Age ≥ 65 years Study period –1998–2001 Method –Influenza activity was defined by laboratory confirmed cases admitted to a general regional hospital –Admissions for pneumonia, acute exacerbations of chronic obstructive pulmonary disease, heart failure and asthma of a regional general hospital were analysed

Excess hospital admissions attributed to influenza Pneumonia148 (101.0–196.2)88.9 (69.8–108.1)55.8 (40.6–71.0)47.1 (24.0–70.2) COPD*67.8 (55.4–80.2)4.7 (0.0–16.2)84.3 (63.3–105.3)35.0 (13.8–56.2) Heart failure166.8 (144.0–189.6)36.9 (18.6–55.2)50.8 (34.8–66.9)5.6 (-8.6–19.8) All three diagnoses (330.4–436.0)130.5 (102.4–158.6)190.9 (161.2–220.6)87.7 (54.2–121.2) * Chronic obstructive pulmonary disease Study 2: major findings Significant correlations were found between total influenza activity and the monthly number of hospital admissions for pneumonia, chronic obstructive pulmonary disease and heart failure

Study 2: conclusions Influenza activity is associated with significant excess hospital admissions among elderly aged ≥ 65 years in Hong Kong, and is comparable to the data reported from Western countries The findings support a wider application of influenza vaccine in this region

Study 3 Influenza-associated mortality in Hong Kong. –Wong CM, Chan KP, Hedley AJ, Peiris JS –Clin Infect Dis 2004; 39: 1611–7

Study 3 Study design –Retrospective population-based study Study period –1996–1999 Method –Number of deaths due to cardiovascular and respiratory diseases, pneumonia and influenza, chronic obstructive pulmonary disease, ischaemic heart disease., and all-cause deaths for Hong Kong were analysed –Laboratory-confirmed influenza admissions in a regional general hospital was used to define influenza activity

Study 3: major findings It was estimated that influenza resulted in a substantial number of deaths from cardiorespiratory disease –7.3 (95% CI: 3.1–11.4) deaths / 100,000 / year among patients aged 40–65 years –102.0 (95% CI: 61.2–142.7) deaths / 100,000 / year among patients aged ≥ 65 years Although respiratory diseases accounted for the majority of influenza-related deaths, influenza also contributed to a substantial proportion of deaths related to ischaemic heart disease –13.8% (95% CI: 4.8–22.7%) among aged patients aged 40– 65 years –5.3% (95% CI: 1.2–9.3%) among aged ≥ 65 years

Study 3: conclusions Influenza is associated with deaths due to ischaemic heart disease as well from respiratory diseases Overall influenza-associated mortality in a region with warm climate, such as Hong Kong, is comparable with that documented in temperate regions The need for influenza vaccination in tropical regions needs to be reassured

By courtesy of APACI Asia-Pacific Advisory Committee on influenza