Despite its name, Haemophilus influenzae type b – or Hib – doesn’t cause influenza. In the 1890s, doctors thought this bacteria might cause flu and – despite later research showing flu is caused by a virus – the name stuck. So what is it?
Haemophilus influenzae disease is a name for any infection caused by bacteria called H. influenzae. These bacteria live in people’s nose and throat, and usually cause no harm. However, the bacteria can sometimes move to other parts of the body and cause infection.
People spread H. influenzae, including Hib, to others through respiratory droplets. This happens when someone who has the bacteria in their nose or throat coughs or sneezes. People who are not sick but have the bacteria in their noses and throats can still spread the bacteria. Experts do not know how long it takes after H. influenzae enter a person’s body for someone to get sick. However, it could take as little as a few days before symptoms appear.
Hib bacteria can cause many types of invasive disease, including meningitis, pneumonia, cellulitis (skin infection), septic arthritis (joint infection), bloodstream infection, and epiglottitis (infection causing obstruction or closing of the windpipe). Prior to 1985 Hib disease was the leading cause of bacterial meningitis among U.S. children under 5 years old. Hib can also cause mild infections like bronchitis or ear infections.
Symptoms depend on the part of the body that is infected. Treatment depends on the kind of infection. Depending on how serious the infection is, people with H. influenzae disease may need care in a hospital. Even with appropriate treatment, some H. influenzae infections can result in long-term problems or death. For example, bloodstream infections can result in loss of limbs. Meningitis can cause brain damage or hearing loss.
In 1892, German physician Richard Pfeiffer isolated a bacterium from the lungs and sputum of influenza patients during a pandemic. Pfeiffer believed that he had found the cause of influenza. However, in the 1930s it was established that influenza is caused by a virus, not bacteria. But the bacteria Pfeiffer had isolated did prove to be useful in identifying several diseases.
In 1931, American researcher Margaret Pittman, PhD classified different types of Haemophilus influenzae bacteria and found that type b (called Hib) caused nearly all cases of Haemophilus influenzae meningitis. It would later be confirmed that Hib could also cause many other serious diseases, including infections of the blood, bone, and joints.
The first vaccine against Hib disease was licensed in the United States in 1985 and was used until 1988. It was replaced by the first conjugate vaccine against Hib. Today there are three conjugate Hib disease vaccines available in the United States, as well as two combination vaccines that provide protection against multiple diseases, including Hib disease.
With widespread use of the vaccine, the number of reported cases of invasive Hib disease in US children has been reduced by 99%.
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