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The most common of these otherwise uncommon complications is infection of the skin due to bacteria invading the open sores of the chicken pox. Most of the time, these skin infections are easily treated with antibiotics by mouth. However, occasionally the infection spreads too fast or does not come under control with oral antibiotics. In these cases, antibiotics by vein are required.
An inflammation or swelling of the brain causing confusion or incoordination may occur. This usually happens after the lesions begin to crust over. Because of this timing, it is felt that this complication called encephalitis is caused by the body's immune reaction rather than the infection itself. Almost always, the child gets better over time without any long lasting consequences. Incoordination or Acute Cerebellar Ataxia is the more common brain complication of chicken pox.
The varicella virus may infect the lungs causing significant swelling within them called pneumonitis. This is most often a complication experienced by adults who get chicken pox, but it can rarely happen to children as well.
There is an association with the Group A Streptococcus bacteria (the same one that causes strep throat) and chicken pox. This bacteria may invade deeper tissues of the body causing life-threatening illness. A more personal perspective about this complication may be found in "Chicken Pox & Group A Strep".