I owe much of the information in this to my experience with influenza (having it in 2003), the CIBA Collection of Medical Illustrations Vol 7 Respiratory System Frank H Netter MD and to the CDC. I was glued to the website in 2003.
Influenza can have some really nasty complications. I just want to go over them because I was inadequately taught about influenza in medical school and residency. It could be my fault because I fell asleep a lot second year, but I had an influenza complication in 2003 that put me out for two months and really took a full year to recover from. The clinic I used to work at thought I was malingering, especially the other doctors, so my impression is that I am not the only doctor who doesn't understand influenza very well. I think we're going to learn fast this year.
Four main complications.
First is "primary influenza viral pneumonia". It develops in one to three days after influenza hits and has a high mortality. Symptoms are high fever, dyspnea and cyanosis (turning blue because of lack of oxygen). People may not cough anything up or may cough up blood. The lungs have diffuse rales, wheezes and generally decreased breath sounds. Usually signs of consolidation are absent. If tracheal secretions are obtained by bronchoscopy, there are no bacterial pathogens or polymorphonuclear leukocytes. Chest x-ray shows diffuse reticulonodular infiltrates that are more prominent in the midlung fields. A severe case can progress to respiratory failure and vascular collapse. Milder cases need rest most of all, until the lung swelling subsides and heartrate returns to normal at rest and ambulating.
Second is influenza complicated by secondary bacterial pneumonia. This usually shows up three to six days after the onset of the influenza. The infection may be segmental or lobar in distribution. It can also show up as a patchy bronchopneumonia. Sputum contains abundant neutrophils and bacteria, of which the principal invaders are Streptococcus pneumonia or Staphyloccus aureus. Other possible pathogens include Streptococcus pyogenes, Klebsiella species and Hemophilus influenza.
Third is "Combined influenza viral and bacterial pneumonia." The onset of diffuse viral pneumonia is followed by pleuritic pain and purulent sputum, suggesting bacterial suprainfection. The x-ray generally shows segmental or lobar consolidation or scattered dense areas of bronchopneumonia. The same bacteria are implicated as in any secondary bacterial pneumonia.
Fourth possible complications are really nasty. Acute rhabdomyolysis and myoglobinuria ..... or myocarditis (an inflamed heart) .... or toxic encephalopathy including Reye's syndrome. These "may develop rarely."
All in all, I think it is important for primary care doctors and emergency room doctors to brush up on the complications of influenza.