A healthy immune system and normal white blood cell count fights bacteria. However, when the white blood cell count is low, the chance of infection increases. 

If your child gets a fever, go to the hospital right away. The doctor will order antibiotics that target bacteria in children with cancer. 

Opportunistic infections only happen when the immune system isn't working well. Infections include fungus (thrush or yeast) and a type of pneumonia called Pneumocystis. 

Your doctor may give your child a medicine called Bactrim or Septrim to help prevent Pneumocystis. 

Children who receive cancer treatment can get common viral illnesses such as colds and diarrhoea. Some viral illnesses such as chicken pox and shingles can be more serious in children with cancer.