Haemophilus influenzae, or H. influenzae, is a kind of bacteria. It can cause bacterial infections ranging from mild (such as bronchitis) to severe (such as septic arthritis). Symptoms depend on the specific. Treatment includes antibiotics but you may also require hospitalization depending on the severity of your condition.
Haemophilus influenzae (H. influenzae) is a type of bacteria that can cause several different kinds of infections. These bacterial infections can range from mild, such as ear infections, to severe, such as bloodstream infections. The infections typically affect children younger than 5 years old. They also affect people who are immunocompromised, such as those with certain medical conditions.
Some H. influenzae infections are “invasive,” which means the bacteria invade parts of your body that are normally free from germs. For instance, H. influenzae can invade the fluid surrounding your spinal cord and brain, which can cause meningitis. Meningitis is the swelling of the lining of your brain and spinal cord. Invasive diseases usually require hospital treatment and can sometimes be fatal.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Haemophilus influenzae bacteria are categorized into encapsulated (typeable) and non-encapsulated (non-typeable). Encapsulated means the bacteria have an outer protective covering. This covering, or capsule, makes them more resistant to antibiotics. Encapsulated bacteria are further separated into subtypes named “a” through “f.”
The most common type of H. influenzae is Haemophilus influenzae type b (Hib). Most often, Hib affects children younger than 5 years of age and adults over 65 years of age. It can also affect people who have weakened immune systems (are immunocompromised), such as those with:
The Hib vaccine can help protect against Haemophilus influenzae type b infections.
Despite its name, Haemophilus influenzae doesn’t cause the flu (influenza). It can cause many other serious diseases, though.
The most common diseases and infections caused by H. influenzae include:
The Hib vaccine is part of the routine childhood immunization schedule. Therefore, H. influenzae diseases primarily affect children who haven’t been vaccinated for Hib type b. It also affects newborns who haven’t completed their vaccination series.
H. influenzae disease incidence is also higher among children native to Alaska, despite vaccination status. Infections occur in 5 out of every 100,000 children of Alaskan descent. People who are 65 or older and people who are immunocompromised are also more commonly affected.
The United States introduced the conjugate Hib vaccine for children in 1987 and for infants in 1990. Before the introduction, about 20,000 children younger than 5 had a severe Hib disease each year and about 1,000 died. Since the introduction of the vaccine, the rate of Hib infections has dropped dramatically. Severe Hib disease cases have dropped by more than 99% since 1991. In 2019, 0.15 out of every 100,000 children younger than 5 years old had a Hib disease.
Now, non-typeable H. influenzae causes the majority of Haemophilus influenzae diseases in all age groups. In 2019, the rate was 1.62 out of every 100,000 children younger than 5 years old. Most cases in children now are in those who are unvaccinated or under-vaccinated. Among adults 65 years of age and older, the incidence of non-typeable H. influenzae was 4.88 per 100,000 people.
Haemophilus influenzae symptoms in babies and children depend on the specific disease that it causes.
Symptoms may include:
Symptoms may include:
Symptoms may include:
Symptoms may include:
Symptoms may include:
Symptoms may include:
Symptoms may include:
Symptoms may include:
Haemophilus influenzae is a type of bacteria that causes certain infections and diseases. There are six subtypes of H. influenzae — type a through type f. Other types of H. influenzae are classified as non-typeable. Type b, or Hib, causes 95% of all severe invasive infections.
These bacteria live in your nose and throat but they usually don’t cause any harm. When the bacteria move to other parts of your body, they can cause infections.
Yes. You can get sick from Haemophilus influenzae if you’re not protected from the bacteria through vaccination.
Haemophilus influenzae type b spreads from person to person through respiratory droplets in coughs and sneezes. The respiratory droplets contain the bacteria, and other people can get sick when they breathe in the droplets. The bacteria also spread when people have lengthy or close contact with a person that has the bacteria in their nose or throat, even if that person doesn’t have symptoms. Scientists believe that Hib can’t survive on non-living surfaces or in the environment.
Experts don’t know the precise incubation period of Haemophilus influenzae. The incubation period is the time it takes for symptoms to develop after an infectious bacteria enters your body. Researchers believe it may take only a few days for symptoms to develop after you’ve been infected.
Your healthcare provider will usually diagnose an H. influenzae infection with one or more laboratory tests. They’ll take a sample of your blood, spinal fluid, joint fluid, pleural fluid or middle ear aspirate. The first test they’ll use is called Gram staining. The Gram stain looks for bacteria in the sample and determines the type of bacteria causing a condition. Your healthcare provider may follow up with a blood or body fluid culture to confirm the presence of the bacteria.
Under a Gram stain, bacteria changes to one of two sets of colors (pink to red or purple to blue). These are categorized as gram-negative or gram-positive. Haemophilus influenzae is gram-negative coccobacillus that appears red under the microscope. Gram-negative bacteria have a hard outer shell that protects them and makes them harder to kill. They’re resistant to most available antibiotics and can find new ways to fight off attacks.
Haemophilus influenzae treatment depends on the type of infection or disease. Treatment usually includes the use of antibiotics to fight the infection. However, H. influenzae can be resistant to antibiotics. Depending on the severity of your condition, you may need additional treatment in the hospital. Treatment may include:
You can protect your child from Haemophilus influenzae type b (Hib) infections with the Hib vaccine. The Centers for Disease Control and Prevention (CDC) recommends all children younger than 2 years old receive the vaccine.
Your child’s healthcare provider will typically give the Hib vaccine in three or four doses. Your infant will get their first dose at 2 months of age. They’ll get their second dose at 4 months old. They’ll get a dose at 6 months old if they’re getting four doses. Then, they’ll complete the series with a booster dose between 12 months old and 15 months old. Approximately 95% to 100% of children develop protective antibody levels of Hib after the primary series.
Your child’s provider may give the Hib vaccine as a stand-alone vaccine [PRP-T (ActHIB), PRP-T (Hiberix) or PRP-OMP (Pedvax HIB)] or as part of a combination vaccine [DTap-IPV-Hib (pentacel) or DTap-IPV-Hib-Hep B (Vaxelis)] A combination vaccine combines more than one vaccine into one shot.
The Hib vaccine prevents infections from Haemophilus influenzae type b. But it doesn’t prevent infections caused by other types of H. influenzae. To prevent other H. influenzae infections, you should keep your child’s hands clean and keep them away from people who are sick. Teach your child how to wash their hands at a young age.
The outlook (prognosis) for H. influenzae infections depends on the type and severity of your child’s condition. With prompt diagnosis and treatment, your child’s healthcare provider may be able to control your child’s infection.
However, even with antibiotic treatment, some H. influenzae infections can cause long-term complications. For example, bloodstream infections can result in the loss of your child’s limbs. Up to 20% of people with meningitis have permanent hearing loss or other neurological issues. About 3% to 6% of all children with a Hib infection die from the disease.
If your child has any symptoms of an H. influenzae infection, you should take them to their healthcare provider right away. Prompt diagnosis and treatment are essential for these types of bacterial infections.
A note from Cleveland Clinic
Haemophilus influenzae can cause mild to severe bacterial infections. The best way to prevent these types of infections is through vaccination. The CDC recommends vaccinating your child against the most common type of H. influenzae, type b. If your child develops any symptoms of an H. influenzae infection, take them to their healthcare provider immediately. The sooner your child receives treatment, the better their chances for survival.
Last reviewed by a Cleveland Clinic medical professional on 05/26/2022.
Learn more about our editorial process.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy