An Overview of Haemophilus Influenzae Type B (Hib)

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Haemophilus influenzae type b (Hib)—not to be confused with seasonal influenza—is a vaccine-preventable disease that is particularly dangerous for young children. Advanced infections can cause potentially serious complications like meningitis, pneumonia, and sepsis.

Hib disease is now rare in the United States, but it continues to be a serious childhood illness in areas where the vaccine isn't widely available.

Symptoms

Hib bacteria get into the body through the nose and mouth, where it can linger for a while without causing any symptoms. In some cases, however, the bacteria spread to the bloodstream and to other parts of the body. This is called invasive Hib disease.

Invasive Hib disease can affect multiple organ systems and lead to serious complications including meningitis, epiglottitis, pneumonia, septic arthritis, cellulitis, and bacteremia.

Meningitis

The most common mark of invasive Hib disease is bacterial meningitis, or swelling around the brain and spine. Prior to widespread vaccination, Hib meningitis occurred in 50 to 65 percent of cases and was the most common cause of bacterial meningitis in kids under five years old.

Symptoms of Hib meningitis include:

  • Fever
  • Headache
  • Confusion, irritability, or otherwise altered mental status
  • Stiff neck
  • Sensitivity to light
  • Nausea and/or vomiting
  • Altered reflexes (in young babies)

Most people with Hib meningitis survive, but the disease can permanently affect their health and development. In the prevaccine era, about 15 to 30 percent of survivors experienced hearing loss or brain damage, and about 3 to 6 percent died—even with appropriate treatment.

Epiglottitis

Hib epiglottitis is when the bacteria infect the epiglottis (the throat tissue that keeps food and liquids from getting into the respiratory tract), sometimes causing swelling so severe it blocks the airway. Epiglottitis occurred in about 17 percent of Hib cases prior to widespread vaccination.

Some symptoms of epiglottitis include:

  • Sore throat that comes on quickly
  • Fever
  • Drooling (especially in children)
  • Change in voice
  • Bluish skin color
  • Stridor, or a high-pitched sound when someone breathes in or out

Pneumonia

Pneumonia (an infection of the lungs) is another common complication of invasive Hib disease, occurring in about 15 percent of cases in the prevaccine era.

Signs and symptoms of pneumonia can vary, but they generally include flu-like symptoms like chills, fever, and nasal congestion, productive cough, chest pain, fast breathing (in children), body aches, fatigue, vomiting (in children), and bluish skin color.

Septic Arthritis

Septic arthritis is a joint infection that happened in roughly 8 percent of Hib cases prior to the introduction of the vaccine. This happens when Hib bacteria infect the joint (typically a large one like a knee or hip), causing significant discomfort.

Symptoms of septic arthritis caused by invasive Hib disease include severe joint pain, difficulty moving affected joint, and redness or swelling around the affected joint.

Cellulitis

Skin infections (or cellulitis) are another common complication of invasive Hib disease. This occurred in roughly 6 percent of pre-vaccination era cases—most often in young children—and typically affected the face, head, or neck. The most common symptom of cellulitis is red, tender, and/or swollen skin.

Bacteremia

Infections that spread to the bloodstream are called bacteremia (also called sepsis). Symptoms of Hib bacteremia include flu-like symptoms, like fever, chills, and fatigue, abdominal pain, nausea and/or vomiting, anxiety, difficulty breathing, and confusion.

Causes

Unlike the similarly named influenza, Haemophilus influenzae is caused by a bacterium (not a virus).

There are multiple types of Haemophilus influenzae, but type b (commonly referred to as Hib), has historically been the most severe.

Before the development of an effective vaccine, Hib caused the overwhelming majority—roughly 95 percent—of serious Haemophilus influenzae infections. 

It’s uncertain exactly how Hib bacteria spread, but scientists think it passes from one person to the next through respiratory droplets (through coughing or sneezing). As a result, people are generally exposed to Hib after being in close contact with someone who is infected, such as at home or in a childcare setting.

Babies whose mothers are infected with Hib can also get exposed to the bacteria by aspirating amniotic fluid or coming into contact with vaginal secretions during delivery. People with Hib infections who don’t have any symptoms can still spread the disease to other people.

New infections start in the nose and throat, where they can be quickly fought off by the immune system or hang out for months without causing any symptoms. Invasive diseases happen when the bacteria get into the bloodstream and go on to infect other parts of the body.

While it’s not exactly clear what causes some cases to jump from a mild infection to an invasive one, it’s possible that other respiratory diseases play a role. For example, if someone is already trying to fight off a virus like influenza, the Hib bacteria might have an easier time spreading in the body. In fact, Hib disease has been a common co-infection during past flu pandemics.

At-Risk Populations

Certain individuals are more like to get invasive Hib disease than others. Like many vaccine-preventable diseases, Hib mainly affects young children. Before widespread vaccination, roughly two-thirds of invasive Hib disease cases occurred in kids under 18 months old, and nearly all were under age five.

Those most likely to get Hib include unvaccinated children and people close to them, as well as individuals with weakened immune systems, including those with certain medical conditions like:

  • Sickle cell disease
  • HIV infection
  • Cancer requiring treatment, such as chemotherapy, radiation, or bone marrow stem cell transplants

Diagnosis

Because Hib can look like a lot of other bacterial infections, doctors often rely on lab tests, in addition to a person’s medical history and physical exam, to diagnose the disease and recommend treatment. If positive for Haemophilus influenzae, local health officials might also want to run tests to figure out if the infection is due to type b or some other subtype.

Physical Exam

Before diagnosing Hib, doctors will first take a medical history and look for signs or symptoms of invasive Hib disease or any of its complications. For young children, in particular, doctors will likely check vaccination records to see if the child has received any or all of the recommended doses of the Hib vaccine.

The doctor might also ask about any contact the child might have had with someone (especially household contacts or caregivers) with a known Hib infection.

Lab Tests

If doctors suspect Hib after a physical exam, they’ll typically confirm the diagnosis by testing body fluids—often blood or spinal fluid—for the bacteria. This can sometimes require a lumbar puncture (or spinal tap) to get a small sample of fluid from the spine.

One of the most common ways labs test samples for Hib bacteria is through a culture, where the sample fluid is placed in a special kind of container to see if Haemophilus influenzae bacteria grow.

Serotyping

If a culture comes back positive for Haemophilus influenzae, it will likely be tested further to determine what strain it is—specifically, whether it’s type b. This is generally done by health authorities (like the local health department) using special tests like slide agglutination or serotype-specific real-time PCR.

Treatment

Hib disease can be treated effectively with antibiotics, but additional care might be needed to help manage symptoms related to complications. People with invasive Hib disease (especially young children) are often hospitalized as a result of the infection.

Antibiotics

The most common medication used to treat Hib is a 10-day course of a third-generation cephalosporin (such as cefotaxime or ceftriaxone) or a combination of chloramphenicol and ampicillin.

Additional Support

Depending on the severity of the infection, individuals with Hib disease might also need treatment to help with symptoms or subsequent complications. These can include breathing support, blood pressure medication, wound care (due to skin infections), amputations (due to bacteremia), or long-term rehabilitation for brain damage or hearing loss (due to meningitis).

Prevention

While Hib can often be effectively treated using antibiotics, the best protection against the disease and its potential complications is by preventing it all together through vaccination. The vaccine is typically administered during early childhood in three or four doses, depending on the brand.

The Centers for Disease Control and Prevention recommends the following groups receive the Hib vaccine:

  • children ages two to 15 months (or up to five years old for catch-up doses)
  • unvaccinated children under age five years who are going through chemotherapy or radiation treatments
  • unvaccinated children under age five with immunoglobulin or early component complement deficiencies
  • unvaccinated children under age 18 years who have an HIV infection
  • anyone (kids or adults) who is unvaccinated and doesn’t have a functional spleen or who has sickle cell disease
  • anyone (kids or adults) who has received a hematopoietic stem cell transplant, even if they’ve been vaccinated against Hib before

While it’s rare, there are some people who shouldn’t be vaccinated against Hib. Those who have had a life-threatening allergic reaction to the Hib vaccine or any of its components shouldn’t get the vaccine, and those experiencing moderate to severe illnesses should wait until they get better before receiving a dose.

If you aren’t sure if you or your child should be vaccinated against Hib, talk to your doctor or health care provider before vaccination.

A Word From Verywell

Hib is extremely rare in the United States. Thanks to vaccines, the number of Hib cases to plummet by more than 99 percent nationwide, and serious complications like Hib meningitis are virtually unheard of now. That said, Hib outbreaks can still happen in areas with low vaccination coverage. The best way to prevent Hib and other vaccine-preventable diseases is by following the CDC’s recommended vaccination schedule.

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