In infancy In infancy, respiratory viruses, particularly rsv, are the most frequent cause but bacterial infection from streptococcus pneumoniae and Haemophilus influenzae are also important. Staphylococcus aureus is uncommon but causes severe infectionIn infancy ◼ In infancy, respiratory viruses, particularly RSV, are the most frequent cause but bacterial infection from Streptococcus pneumoniae and Haemophilus influenzae are also important. Staphylococcus aureus is uncommon but causes severe infection