Haemophilus influenzae, formerly calle Pfeiffer's bacillus or Bacillus influenzae, is a non-motile Gram-negative coccobacillus first described in 1892 by Richard Pfeiffer during an influenza pandemic. A member of the Pasteurellaceae family it is generally aerobic, but can grow as a facultative anaerobe.H. influenzae was mistakenly considered to be the cause of the common flu until 1933, when the viral etiology of the flu became apparent. Still, H. influenzae is responsible for a wide range of clinical diseases.