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Estimating the disease burden of 2009 pandemic influenza A(H1N1) from surveillance and household surveys in Greece.

Sypsa V, Bonovas S, Tsiodras S, Baka A, Efstathiou P, Malliori M, Panagiotopoulos T, Nikolakopoulos I, Hatzakis A - PLoS ONE (2011)

Bottom Line: Per 1,000 symptomatic cases, based on ILI-38 case definition, 416 attended health services, 108 visited hospital emergency departments and 15 were admitted to hospitals.ICU admission rate and CFR were 37 and 17.5 per 100,000 symptomatic cases or 13.4 and 6.3 per 100,000 infections, respectively.Although individuals older than 65 years were the least affected age group in terms of attack rate, they had 55 and 185 times higher risk of ICU admission and CFR, respectively.

View Article: PubMed Central - PubMed

Affiliation: National and Kapodistrian University of Athens, Athens, Greece. ahatzak@med.uoa.gr

ABSTRACT

Background: The aim of this study was to assess the disease burden of the 2009 pandemic influenza A(H1N1) in Greece.

Methodology/principal findings: Data on influenza-like illness (ILI), collected through cross-sectional nationwide telephone surveys of 1,000 households in Greece repeated for 25 consecutive weeks, were combined with data from H1N1 virologic surveillance to estimate the incidence and the clinical attack rate (CAR) of influenza A(H1N1). Alternative definitions of ILI (cough or sore throat and fever>38°C [ILI-38] or fever 37.1-38°C [ILI-37]) were used to estimate the number of symptomatic infections. The infection attack rate (IAR) was approximated using estimates from published studies on the frequency of fever in infected individuals. Data on H1N1 morbidity and mortality were used to estimate ICU admission and case fatality (CFR) rates. The epidemic peaked on week 48/2009 with approximately 750-1,500 new cases/100,000 population per week, depending on ILI-38 or ILI-37 case definition, respectively. By week 6/2010, 7.1%-15.6% of the population in Greece was estimated to be symptomatically infected with H1N1. Children 5-19 years represented the most affected population group (CAR:27%-54%), whereas individuals older than 64 years were the least affected (CAR:0.6%-2.2%). The IAR (95% CI) of influenza A(H1N1) was estimated to be 19.7% (13.3%, 26.1%). Per 1,000 symptomatic cases, based on ILI-38 case definition, 416 attended health services, 108 visited hospital emergency departments and 15 were admitted to hospitals. ICU admission rate and CFR were 37 and 17.5 per 100,000 symptomatic cases or 13.4 and 6.3 per 100,000 infections, respectively.

Conclusions/significance: Influenza A(H1N1) infected one fifth and caused symptomatic infection in up to 15% of the Greek population. Although individuals older than 65 years were the least affected age group in terms of attack rate, they had 55 and 185 times higher risk of ICU admission and CFR, respectively.

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Age-specific incidence of 2009 pandemic influenza A(H1N1) per 100,000 population per week (3-week weighted moving average).For week i and age group j, the incidence of symptomatic H1N1 infection was estimated as:  per 100,000 population per week where ILIij: the estimated number of new ILI cases per 100,000 population per week and PROPij: the proportion of samples testing positive for H1N1. The number of estimated H1N1 infections was obtained by dividing the estimated number of symptomatic H1N1 cases (based on ILI-38 case definition) by 0.36 [22], [23]. (ILI-38: fever >38°C and cough or sore throat, ILI-37: fever 37.1-38°C and cough or sore throat, ARI-38: any two of fever >38°C, cough, sore throat and runny nose, ARI-37: any two of fever 37.1–38°C, cough, sore throat and runny nose).
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pone-0020593-g002: Age-specific incidence of 2009 pandemic influenza A(H1N1) per 100,000 population per week (3-week weighted moving average).For week i and age group j, the incidence of symptomatic H1N1 infection was estimated as: per 100,000 population per week where ILIij: the estimated number of new ILI cases per 100,000 population per week and PROPij: the proportion of samples testing positive for H1N1. The number of estimated H1N1 infections was obtained by dividing the estimated number of symptomatic H1N1 cases (based on ILI-38 case definition) by 0.36 [22], [23]. (ILI-38: fever >38°C and cough or sore throat, ILI-37: fever 37.1-38°C and cough or sore throat, ARI-38: any two of fever >38°C, cough, sore throat and runny nose, ARI-37: any two of fever 37.1–38°C, cough, sore throat and runny nose).

Mentions: The age-specific weekly incidence rates of ILI-38, ILI-37, ARI-38 and ARI-37 are depicted in Figure S1. A steady rise in the number of ILI and ARI cases was observed after week 37 of 2009 (September 7–13, 2009) in most age groups; particularly, among individuals aged 0–4 and 5–19 years. The age-specific incidence rate of H1N1 symptomatic cases and of estimated H1N1 infections is shown in Figure 2. The most affected age group was that of school children/adolescents 5–19 years old with a peak in the incidence occurring during week 48 of 2010 (approximately 3,300–5,800 new H1N1 symptomatic cases per 100,000 population per week, based on ILI-38 and ILI-37 definition, respectively). The overall incidence of ILI/ARI and of H1N1 in the Greek population is depicted in Figure S2 and Figure 3, respectively. The epidemic peaked on week 48 (end of November-beginning of December 2009), with approximately 750–1,500 new H1N1 symptomatic cases per 100,000 population per week, based on ILI-38 and ILI-37 definition, respectively, and was followed by a sharp decline in the following weeks.


Estimating the disease burden of 2009 pandemic influenza A(H1N1) from surveillance and household surveys in Greece.

Sypsa V, Bonovas S, Tsiodras S, Baka A, Efstathiou P, Malliori M, Panagiotopoulos T, Nikolakopoulos I, Hatzakis A - PLoS ONE (2011)

Age-specific incidence of 2009 pandemic influenza A(H1N1) per 100,000 population per week (3-week weighted moving average).For week i and age group j, the incidence of symptomatic H1N1 infection was estimated as:  per 100,000 population per week where ILIij: the estimated number of new ILI cases per 100,000 population per week and PROPij: the proportion of samples testing positive for H1N1. The number of estimated H1N1 infections was obtained by dividing the estimated number of symptomatic H1N1 cases (based on ILI-38 case definition) by 0.36 [22], [23]. (ILI-38: fever >38°C and cough or sore throat, ILI-37: fever 37.1-38°C and cough or sore throat, ARI-38: any two of fever >38°C, cough, sore throat and runny nose, ARI-37: any two of fever 37.1–38°C, cough, sore throat and runny nose).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3111416&req=5

pone-0020593-g002: Age-specific incidence of 2009 pandemic influenza A(H1N1) per 100,000 population per week (3-week weighted moving average).For week i and age group j, the incidence of symptomatic H1N1 infection was estimated as: per 100,000 population per week where ILIij: the estimated number of new ILI cases per 100,000 population per week and PROPij: the proportion of samples testing positive for H1N1. The number of estimated H1N1 infections was obtained by dividing the estimated number of symptomatic H1N1 cases (based on ILI-38 case definition) by 0.36 [22], [23]. (ILI-38: fever >38°C and cough or sore throat, ILI-37: fever 37.1-38°C and cough or sore throat, ARI-38: any two of fever >38°C, cough, sore throat and runny nose, ARI-37: any two of fever 37.1–38°C, cough, sore throat and runny nose).
Mentions: The age-specific weekly incidence rates of ILI-38, ILI-37, ARI-38 and ARI-37 are depicted in Figure S1. A steady rise in the number of ILI and ARI cases was observed after week 37 of 2009 (September 7–13, 2009) in most age groups; particularly, among individuals aged 0–4 and 5–19 years. The age-specific incidence rate of H1N1 symptomatic cases and of estimated H1N1 infections is shown in Figure 2. The most affected age group was that of school children/adolescents 5–19 years old with a peak in the incidence occurring during week 48 of 2010 (approximately 3,300–5,800 new H1N1 symptomatic cases per 100,000 population per week, based on ILI-38 and ILI-37 definition, respectively). The overall incidence of ILI/ARI and of H1N1 in the Greek population is depicted in Figure S2 and Figure 3, respectively. The epidemic peaked on week 48 (end of November-beginning of December 2009), with approximately 750–1,500 new H1N1 symptomatic cases per 100,000 population per week, based on ILI-38 and ILI-37 definition, respectively, and was followed by a sharp decline in the following weeks.

Bottom Line: Per 1,000 symptomatic cases, based on ILI-38 case definition, 416 attended health services, 108 visited hospital emergency departments and 15 were admitted to hospitals.ICU admission rate and CFR were 37 and 17.5 per 100,000 symptomatic cases or 13.4 and 6.3 per 100,000 infections, respectively.Although individuals older than 65 years were the least affected age group in terms of attack rate, they had 55 and 185 times higher risk of ICU admission and CFR, respectively.

View Article: PubMed Central - PubMed

Affiliation: National and Kapodistrian University of Athens, Athens, Greece. ahatzak@med.uoa.gr

ABSTRACT

Background: The aim of this study was to assess the disease burden of the 2009 pandemic influenza A(H1N1) in Greece.

Methodology/principal findings: Data on influenza-like illness (ILI), collected through cross-sectional nationwide telephone surveys of 1,000 households in Greece repeated for 25 consecutive weeks, were combined with data from H1N1 virologic surveillance to estimate the incidence and the clinical attack rate (CAR) of influenza A(H1N1). Alternative definitions of ILI (cough or sore throat and fever>38°C [ILI-38] or fever 37.1-38°C [ILI-37]) were used to estimate the number of symptomatic infections. The infection attack rate (IAR) was approximated using estimates from published studies on the frequency of fever in infected individuals. Data on H1N1 morbidity and mortality were used to estimate ICU admission and case fatality (CFR) rates. The epidemic peaked on week 48/2009 with approximately 750-1,500 new cases/100,000 population per week, depending on ILI-38 or ILI-37 case definition, respectively. By week 6/2010, 7.1%-15.6% of the population in Greece was estimated to be symptomatically infected with H1N1. Children 5-19 years represented the most affected population group (CAR:27%-54%), whereas individuals older than 64 years were the least affected (CAR:0.6%-2.2%). The IAR (95% CI) of influenza A(H1N1) was estimated to be 19.7% (13.3%, 26.1%). Per 1,000 symptomatic cases, based on ILI-38 case definition, 416 attended health services, 108 visited hospital emergency departments and 15 were admitted to hospitals. ICU admission rate and CFR were 37 and 17.5 per 100,000 symptomatic cases or 13.4 and 6.3 per 100,000 infections, respectively.

Conclusions/significance: Influenza A(H1N1) infected one fifth and caused symptomatic infection in up to 15% of the Greek population. Although individuals older than 65 years were the least affected age group in terms of attack rate, they had 55 and 185 times higher risk of ICU admission and CFR, respectively.

Show MeSH
Related in: MedlinePlus