Mortality, Severe Acute Respiratory Infection, and Influenza-Like Illness Associated with Influenza A(H1N1)pdm09 in Argentina, 2009

<div><h3>Introduction</h3><p>While there is much information about the burden of influenza A(H1N1)pdm09 in North America, little data exist on its burden in South America.</p> <h3>Methods</h3><p>During April to December 2009, we actively searched for persons with severe acute respiratory infection and influenza-like illness (ILI) in three sentinel cities. A proportion of case-patients provided swabs for influenza testing. We estimated the number of case-patients that would have tested positive for influenza by multiplying the number of untested case-patients by the proportion who tested positive. We estimated rates by dividing the estimated number of case-patients by the census population after adjusting for the proportion of case-patients with missing illness onset information and ILI case-patients who visited physicians multiple times for one illness event.</p> <h3>Results</h3><p>We estimated that the influenza A(H1N1)pdm09 mortality rate per 100,000 person-years (py) ranged from 1.5 among persons aged 5–44 years to 5.6 among persons aged ≥65 years. A(H1N1)pdm09 hospitalization rates per 100,000 py ranged between 26.9 among children aged <5 years to 41.8 among persons aged ≥65 years. Influenza A(H1N1)pdm09 ILI rates per 100 py ranged between 1.6 among children aged <5 to 17.1 among persons aged 45–64 years. While 9 (53%) of 17 influenza A(H1N1)pdm09 decedents with available data had obesity and 7 (17%) of 40 had diabetes, less than 4% of surviving influenza A(H1N1)pdm09 case-patients had these pre-existing conditions (p≤0.001).</p> <h3>Conclusion</h3><p>Influenza A(H1N1)pdm09 caused a similar burden of disease in Argentina as in other countries. Such disease burden suggests the potential value of timely influenza vaccinations.</p> </div

Rates of influenza A(H1N1)pdm09-associated mortality among influenza-like illness (ILI) cases at three sentinel cities in Argentina, according to age group. April–December, 2009.

a<p>Estimated by multiplying the <u>week-specific</u> number of decedents identified (row 1) by the <u>week-specific</u> proportion testing positive for 2009 H1N1 (row 2) and its 95% confidence interval.</p>b<p>Corrected for the proportion of case-patients missing date of illness onset (epidemiologic week) information (i.e. 2 of 39 among persons aged 45–64 years and 2 of 27 among persons aged ≥65 years).</p

Description of case-patients with available risk factor data identified during active case-finding in 2009 and during three consecutive health utilization surveys in 2010, three cities in Argentina.

<p>2009 H1N1 denotes influenza A (H1N1)pdm09, SARI denotes severe acute respiratory illness, and ILI denotes influenza-like illness.</p>a<p>among cases with available age, pregnancy, obesity, chronic obstructive pulmonary disease, or asthma status data.</p>b<p>The age of case-patients is significantly associated with decedent, SARI, or ILI case-status in linear regression (p≤0.001).</p>c<p>The sex of case-patients is significantly associated with decedent, SARI, or ILI case-status in Fisher Exact testing (p = 0.01).</p>d<p>The characteristic is significantly associated with decedent, SARI, or ILI case-status in Fisher Exact testing (p<0.001).</p

Rates of influenza A(H1N1)pdm09-associated influenza-like illness case-patients at three sentinel cities in Argentina, according to age group April–December, 2009.

a<p>Estimated by multiplying the week-specific number of ILI cases identified (row 1) by the proportion testing positive for 2009 H1N1 (row 3) and its 95% confidence interval by the proportion of ILI cases among ILI physician visits (row 4) while adjusting for the proportion of cases-patients missing data on their epidemiologic week of illness.</p>b<p>Corrected for the proportion of case-patients missing date of illness onset (epidemiologic week) information (i.e. 95 of 2,365 among children aged <5 years, 688 of 16,204 among persons aged 5–44, 101 of 2725 among persons aged 45–64 years, and 63 of 1180 among persons aged ≥65 years).</p

Rates of influenza A(H1N1)pdm09-associated severe acute respiratory case-patients at three sentinel cities in Argentina, according to age group May–December, 2009.

a<p>Estimated by multiplying the <u>week-specific</u> number of decedents identified (row 1) by the <u>week-specific</u> proportion testing positive for 2009 H1N1 (row 2) and its 95% confidence interval.</p>b<p>Corrected for the proportion of case-patients missing date of illness onset (epidemiologic week) information (i.e. 1 of 271 among children aged <5 years, 7 of 748 among persons aged 5–44, 6 of 350 among persons aged 45–64 years, and 1 of 253 among persons aged ≥65 years).</p

Distribution of influenza A(H1N1)pdm09-associated case-patients in three cities in Argentina by epidemiologic week, May–December 2009.

<p>Distribution of influenza A(H1N1)pdm09-associated case-patients in three cities in Argentina by epidemiologic week, May–December 2009.</p

Influenza cases reported to the national influenza surveillance system by each participating country (from southern- to northern-most) and percentages of cases due to influenza type B virus.

<p>Influenza cases reported to the national influenza surveillance system by each participating country (from southern- to northern-most) and percentages of cases due to influenza type B virus.</p

Mean percentage of influenza cases by month (black diamonds) and number of times the peak of the influenza season took place in each month (pink squares) for countries of Northern hemisphere.

<p>Mean percentage of influenza cases by month (black diamonds) and number of times the peak of the influenza season took place in each month (pink squares) for countries of Northern hemisphere.</p

Median percentage of influenza cases that occurred during the 3-month peak period and median number of months to have ≥80% of influenza cases during a season by zone (Southern hemisphere, inter-tropical belt, Northern hemisphere) and proportion of influenza B.

<p>Median percentage of influenza cases that occurred during the 3-month peak period and median number of months to have ≥80% of influenza cases during a season by zone (Southern hemisphere, inter-tropical belt, Northern hemisphere) and proportion of influenza B.</p

Mean percentage of influenza cases by month (black diamonds) and number of times the peak of the influenza season took place in each month (pink squares) for countries in the inter-tropical belt.

<p>Mean percentage of influenza cases by month (black diamonds) and number of times the peak of the influenza season took place in each month (pink squares) for countries in the inter-tropical belt.</p