Ans. is 'a' i.e., Streptococcus pneumoniae o Streptococcus pneumoniae is the most common cause of meningitis in adults older than 20 years of age.o A number of predisposing conditions increase the risk of pneumococcal meningitis, the most common of which is pneumonia.o Additional risk factors include alcoholism, acute and chronic otitis media, diabetes, splenectomy, hypogamaglobulinemia and head trauma with basilar skull fracture and CSF leak.