In 1939, Margaret Pittman showed that sulfapyradine was effective against nontype-specific Haemophilus influenzae. Pittman discovered that there are six identifiable strains of H. influenzae (a through f) bacteria that are encapsulated in a polysaccharide outer coating.

She drew attention to the fact that H. influenzae type b, or Hib, was the serotype that most often caused serious infections, sometimes leading to blindness and even death in young children. Her work eventually led others to develop effective vaccines against Hib.