The incubation period of influenza is 2 to 4 days and varies with viral strain and host factors, such as age and underlying conditions. Classically, the onset of symptoms is acute and usually includes fever, chills, headache, sore throat, dry cough, and myalgias. Otitis media and conjunctivitis can also occur. Any part of the respiratory tract can be affected, and although upper respiratory tract symptoms are most common, croup, bronchitis, and pneumonia can also develop. Pneumonia can be either due to the virus itself or due to a secondary bacterial infection and the two are difficult to distinguish. The development of productive cough and lobar consolidation on chest radiograph are suggestive of the latter. In older children, acute calf pain and refusal to walk may indicate benign and self-limited myositis, more often following influenza B than influenza A. Young children may present with fever alone (“rule out sepsis”) or may have gastrointestinal symptoms such as vomiting, abdominal pain, and diarrhea. Infants may present with apnea. Rarely, influenza can cause myocarditis, seizures, encephalopathy, encephalitis, transverse myelitis, or Guillain–Barré syndrome. In Japan, a severe, acute necrotizing encephalopathy due to influenza has been reported in young children. It is associated with rapid progression to seizures and coma.6 Reye syndrome can develop when aspirin is used during influenza infection but the incidence of this syndrome has decreased greatly with the widespread use of acetaminophen or ibuprofen for fever in children. Deaths usually occur due to complications, including secondary bacterial infections. In December 2006 and January 2007, for example, the CDC reported an increased number of deaths in children coinfected with influenza and community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) pneumonia and an advisory was issued alerting health care professionals to this trend.7 During the 2009 to 2010 influenza A (H1N1) pandemic, secondary complications of influenza A (pH1N1) that were risk factors for mortality were myocarditis, encephalitis, and clinical diagnosis of early presumed CA-MRSA coinfection of the lung.8