Haemophilus influenzae type b
Haemophilus influenzae type b (Hib) is a serious bacterial infection that can cause life-threatening illnesses such as meningitis, pneumonia, epiglottitis, and bloodstream infections, particularly in children under the age of five. Before the introduction of effective vaccines, Haemophilus influenzae type b was one of the leading causes of bacterial meningitis in young children around the world. Although it no longer poses the same threat in countries with widespread vaccination programmes, it remains a concern in regions with limited healthcare access.
Hib is a type of Haemophilus influenzae bacterium, a family of bacteria that can inhabit the upper respiratory tract. While many strains are harmless, type b is particularly aggressive. It has the ability to invade the bloodstream and spread to critical organs, causing severe and sometimes fatal disease. Early detection and prevention through immunisation remain the most effective ways to control this dangerous pathogen.
What is Haemophilus influenzae type b?
Haemophilus influenzae type b is a gram-negative coccobacillus bacterium that primarily affects infants and young children. It is one of six types (a through f) of encapsulated Haemophilus influenzae. The “type b” designation refers to the specific structure of the bacterium’s outer capsule, which is what makes it more virulent than other strains.
Hib is not a virus, and despite its name, it has no relation to influenza (the flu). The confusion arose historically when the bacterium was first identified during an influenza outbreak in the late 19th century.
Who is at Risk?
Children under five, especially those aged between 6 months and 2 years
Unvaccinated infants and toddlers
People with weakened immune systems, such as those undergoing chemotherapy or living with HIV/AIDS
Indigenous populations in certain countries, where the disease remains more prevalent
Elderly adults with underlying health conditions, although this is far less common
Without vaccination, Hib can spread rapidly, particularly in crowded settings like day-care centres and schools.
How is Hib Transmitted?
The bacteria are spread via respiratory droplets when an infected person:
Coughs
Sneezes
Talks at close range
Once inhaled, Hib can colonise the upper respiratory tract and either remain harmless or invade deeper tissues. It can spread to the bloodstream and then to the brain, lungs, bones, or joints.
Diseases Caused by Hib
Haemophilus influenzae type b is responsible for several invasive diseases, including:
1. Meningitis
Infection of the membranes surrounding the brain and spinal cord
Symptoms: high fever, stiff neck, vomiting, irritability, drowsiness
Can lead to permanent brain damage or death if untreated
2. Epiglottitis
Swelling of the epiglottis (the flap at the back of the throat)
Symptoms: difficulty breathing, drooling, high fever, anxiety
Medical emergency requiring immediate intervention
3. Pneumonia
Infection of the lungs
Symptoms: cough, difficulty breathing, chest pain, fever
Common in both children and older adults
4. Sepsis (Bloodstream Infection)
Bacteria enter the bloodstream and spread rapidly
Symptoms: fever, rapid heartbeat, low blood pressure, confusion
Can progress quickly to septic shock
5. Septic Arthritis
Infection of a joint, usually the hip or knee
Causes pain, swelling, redness, and restricted movement
6. Osteomyelitis
Infection of the bone
Leads to localised pain, fever, and swelling
Even with antibiotics, these conditions can result in long-term complications or death, particularly in young children.
Global Impact and Vaccination Success
Prior to the introduction of the Hib vaccine:
Hib caused an estimated 400,000 deaths annually in children under five
Developed countries saw thousands of cases of meningitis and epiglottitis each year
Today, in countries with effective immunisation campaigns:
Hib disease is rare
Routine infant immunisation has reduced incidence by over 95%
Outbreaks are largely confined to under-vaccinated communities
Unfortunately, in parts of sub-Saharan Africa, Asia, and Latin America, Hib continues to be a public health concern, especially where vaccination coverage is low or interrupted by conflict or poverty.
Prevention is Key
The most effective way to prevent Hib is through routine vaccination, usually administered as part of a combination vaccine (e.g. DTaP-IPV-Hib). The vaccine is:
Given in multiple doses, starting from 6 weeks of age
Highly effective, with few side effects
Often combined with protection against diphtheria, tetanus, pertussis, and polio
Herd immunity plays a significant role in protecting vulnerable populations, such as infants too young to be vaccinated or individuals with immunodeficiencies.
Conclusion | Haemophilus influenzae type b
Haemophilus influenzae type b is a dangerous bacterial infection that once claimed thousands of lives every year. Thanks to effective vaccines, it is now preventable in most parts of the world. However, ongoing vigilance and sustained immunisation efforts are vital to keeping Haemophilus influenzae type b under control—particularly in low-income regions where children remain at risk.
