Explore the recorded discovery and history of Haemophilus influenzae, with source links and stated limits.
H. influenzae lives in the nose and throat of many healthy people and usually causes no harm. Some strains carry a polysaccharide capsule; capsular type b (Hib) caused most invasive childhood disease before Hib conjugate vaccines, while unencapsulated nontypeable strains are the ones most often carried. Despite the name it does not cause influenza: that association was proposed during an 1892 outbreak investigation and corrected once influenza was shown to be viral in 1933. Reported infections range from ear infection and bronchitis to pneumonia, bloodstream infection and meningitis, and CDC states that symptoms depend on which part of the body is infected.
CDC credits Richard Pfeiffer in 1892, who found the bacterium in the sputum of patients during an influenza outbreak and proposed a causal association with influenza. The observation location is not evidence of the organism’s origin.
The curated nomenclature record gives Lehmann and Neumann 1896 as the basonym authority for the name Bacterium influenzae.
LPSN records the current name as (Lehmann and Neumann 1896) Winslow et al. 1917, on the Approved Lists of 1980, with type strain ATCC 33391 / NCTC 8143. CDC’s Pink Book instead dates the Winslow naming to 1920; this profile shows the curated nomenclature date and records the discrepancy.
In 1931 Margaret Pittman observed that strains from acute invasive disease tended to be capsulated with smooth colonies, while strains from the upper respiratory tract of healthy people tended to lack a capsule. Her work separated capsular types a-f, and CDC notes that virtually all isolates from cerebrospinal fluid and blood were type b.
CDC states that it was not until 1933 that influenza was established to be caused by a virus and H. influenzae to be a cause of secondary infection. The species name records the earlier mistaken association.
These references do not establish the first person ever infected. Discovery, naming and isolation milestones do not date biological origin or a patient zero.
Source check: 2026-09-19. Educational content; independent scientific review remains pending.