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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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Proportion of samples testing positive for 2009 pandemic influenza A(H1N1) by RT-PCR over time.All samples (15,494 samples tested positive out of a total of 37,960 samples) and according to age group (number testing positive/total tested: 706/2865, 4431/7719, 1966/4194, 2442/6996, 996/3145, 380/2779 for the age groups 0–4, 5–19, 20–29, 30–49, 50–64, and 65+ years, respectively).
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pone-0020593-g001: Proportion of samples testing positive for 2009 pandemic influenza A(H1N1) by RT-PCR over time.All samples (15,494 samples tested positive out of a total of 37,960 samples) and according to age group (number testing positive/total tested: 706/2865, 4431/7719, 1966/4194, 2442/6996, 996/3145, 380/2779 for the age groups 0–4, 5–19, 20–29, 30–49, 50–64, and 65+ years, respectively).

Mentions: The estimate of the incidence of symptomatic influenza A(H1N1) was based on the weekly age-specific ILI rate data, obtained from the phone surveys, and the data on the proportion of samples testing positive for H1N1 out of the total number of samples sent to laboratories from hospitals in the corresponding weeks. We assumed 90% sensitivity for the RT-PCR test [24]. We have applied the age-specific estimates of the proportion of samples testing positive on the corresponding age-specific ILI rates to obtain the number of H1N1 cases as the proportion testing positive varied largely according to age (Figure 1). Thus, for a particular week i and age group j where ILIij: the estimated number of new ILI cases per 100,000 population and PROPij: the proportion of samples testing positive for H1N1, the incidence of symptomatic H1N1 cases was estimated as: per 100,000 population per week. Alternative incidence estimates were obtained using the number of ILI-38, ILI-37, ARI-38 and ARI-37 cases in this formula. A refinement of this method would be possible by taking into account of the variability of the estimates of ILIij and PROPij obtained by the weekly samples.


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)

Proportion of samples testing positive for 2009 pandemic influenza A(H1N1) by RT-PCR over time.All samples (15,494 samples tested positive out of a total of 37,960 samples) and according to age group (number testing positive/total tested: 706/2865, 4431/7719, 1966/4194, 2442/6996, 996/3145, 380/2779 for the age groups 0–4, 5–19, 20–29, 30–49, 50–64, and 65+ years, respectively).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0020593-g001: Proportion of samples testing positive for 2009 pandemic influenza A(H1N1) by RT-PCR over time.All samples (15,494 samples tested positive out of a total of 37,960 samples) and according to age group (number testing positive/total tested: 706/2865, 4431/7719, 1966/4194, 2442/6996, 996/3145, 380/2779 for the age groups 0–4, 5–19, 20–29, 30–49, 50–64, and 65+ years, respectively).
Mentions: The estimate of the incidence of symptomatic influenza A(H1N1) was based on the weekly age-specific ILI rate data, obtained from the phone surveys, and the data on the proportion of samples testing positive for H1N1 out of the total number of samples sent to laboratories from hospitals in the corresponding weeks. We assumed 90% sensitivity for the RT-PCR test [24]. We have applied the age-specific estimates of the proportion of samples testing positive on the corresponding age-specific ILI rates to obtain the number of H1N1 cases as the proportion testing positive varied largely according to age (Figure 1). Thus, for a particular week i and age group j where ILIij: the estimated number of new ILI cases per 100,000 population and PROPij: the proportion of samples testing positive for H1N1, the incidence of symptomatic H1N1 cases was estimated as: per 100,000 population per week. Alternative incidence estimates were obtained using the number of ILI-38, ILI-37, ARI-38 and ARI-37 cases in this formula. A refinement of this method would be possible by taking into account of the variability of the estimates of ILIij and PROPij obtained by the weekly samples.

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