H. influenzae—it ain’t the flu, but it’s still pretty cool

This was first posted at Science-Based Medicine on Monday, but I can’t seem to keep myself from cross-posting. –PalMD

I’ve been thinking about an interesting organism lately, an organism that illustrates some basic principles in science-based medicine.

The organism is called Haemophilus influenzae (H flu), a gram-negative bacterium discovered in the late 19th century. H flu has a great story, both in historic and modern times.

The brilliant microbiologist Richard Pfeiffer isolated H flu from influenza patients in the late 1800’s (hence its name) and for many years, it was believed to be the cause of the epidemic illness, and when the flu pandemic of 1918 hit, researchers worked tirelessly to develop anti-sera against H flu.

But some things weren’t adding up. As thousands died of the flu, doctors were isolating H flu from victims, but also other virulent bacteria such as Streptococcus pneumoniae. Influenza was decimating military camps, and was seriously degrading our ability to fight in WW I, so military bases were a focus of research. Doctors looked for H flu in patients, but could not find it consistently. For example in Camp Dodge, Iowa, an autopsy series showed H flu in only 9.6% of victims.

Some researchers were focusing on something else.

It was found that when sputum of flu victims was sent through filters too small for bacteria to pass through, it was still infectious. These “filterable agents” were known as “viruses”. But even into the 1920’s and 1930’s, it was not clear if H flu played a significant role in influenza, or if a virus was to blame. Interestingly, at a time when women couldn’t yet vote, women physicians and scientists were at the forefront of this medical battle.

As the evidence mounted, the decades-old belief about the role of H flu in influenza (which was held with some skepticism) was abandoned, but the world wasn’t done with H flu.

H flu doesn’t cause “the flu”, but it does cause some pretty nasty human diseases, especially in children. It was a common cause of ear infections, pneumonia, meningitis, and epiglottitis. The last is especially frightening. A toddler may begin with a sore throat, and rapidly progress to difficulty swallowing and breathing. If not treated quickly, the child asphyxiates. Taken together, H flu in children had a fatality rate of about 5-6%.

Since a vaccine against H flu subtype b (Hib) became routine in 1990, the incidence of H flu disease in children has decreased by about 99%, from around 40-100 cases per 100,000 to about 1 case per 100,000.

This is one of the great vaccine success stories. From personal experience, I can tell you that few things are as grave as standing in front of a parent clutching a child who is struggling for breath, drooling, and speaking only enough to say, “Mommy, help!”

The infectious disease promotion folks, such as “Dr.” Jay Gordon may want to read a little history, a little microbiology, and a little epidemiology before telling others to endanger their children.


Barry, John M. The Great Influenza: The Epic Story of the Deadliest Plague in History. Published by Penguin, 2005. ISBN 0143036491, 9780143036494

Wollstein, M.D., Martha. Pfeiffer’s bacillus and influenza, a serologic study. Laboratories of the Rockefeller Institute for Medical Research. 15 July 1919.

Coca, Arthur F., Kelley, Margaret F. A Serological study of the bacillus of Pfeiffer. New York Hospital and the Department of Bacteriology in Cornell University Medical College, New York City. December 13, 1920.