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