Severe acute respiratory infections, including influenza, are a leading cause of cardiopulmonary morbidity and mortality worldwide. Until recently, the epidemiology of influenza was limited to resource-rich countries. Emerging epidemiological reports characterizing the 2009 H1N1 pandemic, however, suggest that influenza exerts an even greater toll in low-income, resource-constrained environments where it is the cause of 5% to 27% of all severe acute respiratory infections. The increased burden of disease in this setting is multifactorial and likely is the result of higher rates of comorbidities such as human immunodeficiency virus, decreased access to health care, including vaccinations and antiviral medications, and limited healthcare infrastructure, including oxygen therapy or critical care support. Improved global epidemiology of influenza is desperately needed to guide allocation of life-saving resources, including vaccines, antiviral medications, and direct the improvement of basic health care to mitigate the impact of influenza infection on the most vulnerable populations.

Highlights

• The epidemiology of influenza is largely based on data from developed countries.
• Emerging data indicate that influenza is the etiology of 8% to 40% of influenza-like illness and 5% to 27% of severe acute respiratory illness in low-income countries.
• The lack of access to health care and adequate healthcare infrastructure portends a disproportionate burden of influenza disease in resource-constrained environments.
• Cardiopulmonary comorbidities are important risk factors for severe influenza.
• Improved influenza surveillance is needed to guide resource allocation and basic healthcare infrastructure development.