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

INTRODUCTION 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. METHODS 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. RESULTS 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). CONCLUSION 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.