1. Etiology 1.1 Pathogens: Main pathogens: Neissria meningitidis, streptoccus pneumoniae, Haemophilus influenzae. (2/3 of purulent meningitis are caused by these pathogens) Pathogens in special populations(neonate <3mo infants, malnutrition, immunodeficiency) gramnegative enteric bacilli, group B streptococci, staphlococcus aureus1.Etiology 1.1 Pathogens:  Main pathogens: Neissria meningitidis, streptoccus pneumoniae, Haemophilus influenzae. (2/3 of purulent meningitis are caused by these pathogens)  Pathogens in special populations (neonate & <3mo infants , malnutrition, immunodeficiency): gramnegative enteric bacilli, group B streptococci, staphlococcus aureus