Complications of Viral Influenza

Viral influenza is a seasonal infection associated with significant morbidity and mortality. In the United States more than 35,000 deaths and 200,000 hospitalizations due to influenza occur annually, and the number is increasing. Children aged less than 1 year and adults aged more than 65 years, pregnant woman, and people of any age with comorbid illnesses are at highest risk. Annual vaccination is the cornerstone of prevention, but some older patients may derive less benefit from immunization than otherwise fit individuals. If started promptly, antiviral medications may reduce complications of acute influenza, but increasing resistance to amantadine and perhaps neuraminidase inhibitors underscores the need for novel prevention and treatment strategies. Pulmonary complications of influenza are most common and include primary influenza and secondary bacterial infection. Either may cause pneumonia, and each has a unique clinical presentation and pathologic basis. Staphylococcus aureus, including methicillin-resistant strains, is an important cause of secondary bacterial pneumonia with high mortality. During influenza season, treatment of pneumonia should include empiric coverage for this pathogen. Neuromuscular and cardiac complications are unusual but may manifest in persons of any age.