What Is Haemophilus Influenzae

  • Asma shaikhDoctor of pharmacy - Done pharm-D from jinnah Sindh medical university Karachi pakistan
  • Asra RunissaMaster of Science - MS, medical biochemistry Kasturba Medical College, Mangalore

The bacteria Haemophilus influenzae can cause a range of infections in humans. H. influenzae is a tiny, gram-negative coccobacillus bacteria that regularly colonizes the upper respiratory system, including the nose and throat, in both children and adults. It can be present as a harmless commensal (normal flora) in some people. However, under specific settings, it can cause diseases ranging from simple respiratory infections to serious invasive disorders. 

It is important to highlight, however, that H. influenzae has no connection to the influenza virus. The influenza virus is a viral pathogen that causes the flu, which is characterized by respiratory symptoms, whereas Haemophilus influenzae is a bacterium that can cause respiratory tract infections such as otitis media, sinusitis, and pneumonia, as well as more serious invasive infections such as meningitis and sepsis (primarily associated with the Hib strain).1

Haemophilus influenza (H. influenzae) is classified into different types based on the presence or absence of a polysaccharide capsule surrounding the bacterium:

  1. Encapsulated H. influenzae

Encapsulated H. influenzae strains have a polysaccharide capsule, which acts as an outer covering that covers the bacterial cell. The capsule shields the bacterium from the immune system and contributes to its pathogenicity.

Based on the material of the capsule, encapsulated H. influenzae strains are further classified into six serotypes, designated as serotypes a, b, c, d, e, and f. Serotype b (Hib) is the most clinically relevant serotype, having been linked to severe invasive infections in children. Serotypes a, c, d, e, and f are less prevalent and have a lower pathogenicity in general.

  1. Unencapsulated H. influenzae: 

H. influenzae that lacks or has a poorly formed polysaccharide capsule. These strains are unable to manufacture capsules or contain capsules that are non-immunogenic. Non-encapsulated are associated with otitis media, sinusitis, bronchitis, and pneumonia are more typically associated with non-encapsulated otitis media.


Haemophilus influenzae (H. influenzae) is a bacterium that can infect people and cause a variety of diseases.H. influenzae is a small, gram-negative bacterium that commonly colonizes the upper respiratory tract, particularly the nose and throat. It can exist as encapsulated and non-encapsulated strains. H. influenzae is typically spread by infected people's respiratory droplets. Close contact with respiratory secretions, such as coughing or sneezing, or exchanging contaminated objects, can help spread the virus. H.influenzae infections are diagnosed using laboratory procedures such as bacterial culture and identification from relevant specimens.

Antibiotic therapy is usually prescribed depending on the kind and severity of the infection, as well as antibiotic susceptibility tests. Vaccination is an important prophylactic measure for H. influenzae infections. The Hib vaccine is indicated for newborns and young children to protect against Hib-related illnesses.

Causes of haemophilus influenzae

Haemophilus influenzae (H. influenzae) is caused by the bacterium's transmission and colonisation in susceptible individuals. The following are the most common causes of H. influenzae infections:

  1. H. influenzae is generally transmitted through respiratory droplets from sick people. 
  2. H. influenzae regularly colonises both children's and adults' upper respiratory tracts, including the nose and throat.
  3. Susceptibility: Individual susceptibility to H. influenzae infections varies. Certain variables can raise the likelihood of contracting an illness, including:
    • Age: Infants and young children, particularly those who have not received the Hib vaccine, are more vulnerable to severe H. influenzae infections, especially those caused by the serotype b strain (Hib). Individuals with low immune systems, as well as the elderly, are at a higher risk.

Signs and symptoms of haemophilus influenzae

Infections with Haemophilus influenzae (H. influenzae) can induce a variety of signs and symptoms, depending on the kind of infection and the site of infection. Here are some of the most common signs and symptoms of H. influenzae infections:

  • Infections of the respiratory tract:
    • Otitis media symptoms include ear pain, earache, hearing loss, fluid pouring from the ear, and fever (which is most frequent in children).
    • Sinusitis is characterised by facial pain or pressure, headache, nasal congestion, thick nasal discharge, and fever.
    • Bronchitis is characterised by a persistent cough, productive cough (with phlegm or mucus), chest discomfort or pain, wheezing, shortness of breath, and fever.
    • Cough (frequently with the formation of yellow or greenish sputum), fever, chest pain.
  • Invasive infections include:
    • Meningitis symptoms include severe headaches, neck stiffness, high temperature, light sensitivity (photophobia), altered mental status, and convulsions.
    • High temperature.
    • Epiglottitis (rare but severe), sore throat, difficulty swallowing, high temperature, muffled voice, drooling, respiratory distress, bending forward to breathe, stridor (high-pitched cough).2

Management and treatment for haemophilus influenzae

The management and treatment of Haemophilus influenzae (H. influenzae) infections depend on the type and severity of the infection.

Antibiotic Treatment

Antibiotics are commonly used to treat H. influenzae infections. Several factors influence antibiotic selection, including the location and severity of infection, the strain of H. influenzae involved, and antibiotic susceptibility testing.

  • Antibiotics often used for non-severe respiratory tract infections caused by non-encapsulated H. influenzae include amoxicillin, amoxicillin-clavulanate, or macrolides such as azithromycin or clarithromycin.
  • Intravenous antibiotics, such as ceftriaxone or cefotaxime, are commonly used for severe infections or invasive illnesses.

Supportive treatment:

To reduce specific symptoms and give comfort, symptomatic treatment might be provided.

  • Over-the-counter pain medicines (e.g., acetaminophen or ibuprofen) may help alleviate pain, fever, and inflammation associated with respiratory tract infections.
  • Adequate hydration, rest, and proper respiratory hygiene (for example, coughing or sneezing into a tissue or the elbow) are often advised.


Haemophilus influenzae (H. influenzae) infections are normally diagnosed using a combination of clinical examination, laboratory investigations, and bacterium identification from relevant specimens.

  1. Clinical Evaluation: The healthcare professional will review your medical history, conduct a physical exam, and ask about your symptoms.
  1. Laboratory Examinations:
    • Culture: A sample from the infected location, such as blood, cerebrospinal fluid (CSF), ear discharge, sputum, or a throat swab, is obtained and cultured in a laboratory.
    • Gramme Staining: Gramme staining is frequently used on clinical samples to provide an early indication of the type of bacteria present. Under the microscope, H. influenzae appears as tiny, gram-negative rods.
    • Rapid Antigen Detection Tests (ADTs): ADTs can be used to identify H. influenzae antigens in clinical samples. This can provide a swift preliminary diagnosis, especially for invasive illnesses like tuberculosis.3
  1. Bacterial Identification: 
    • Serotyping: If H. influenzae is cultured, serotyping can be conducted to determine the bacteria's serotype.
    • PCR assays can be used to detect specific genetic material (DNA or RNA) of H. influenzae, allowing for a more accurate and rapid diagnosis. PCR-based approaches are also capable of distinguishing between encapsulated and non-encapsulated bacteria.
  1. Antibiotic Susceptibility Testing: 

Once the existence of H. influenzae is confirmed, further testing may be performed to determine the bacterium's susceptibility to various antibiotics. This aids in the selection of antibiotics.


How can I prevent haemophilus influenzae

Infections caused by H. influenzae can be avoided with 

  • Routine immunisation
  • Vaccination
  • Basic hygiene practices: Covering one's mouth and nose, disposing of used tissues, avoiding close contact, and urging others to do the same are all examples of good respiratory hygiene.
  • Hand hygiene entails using soap and water or alcohol-based sanitisers on a regular basis. 
  • Avoiding the sharing of personal items reduces the danger of transmission. 
  • Maintaining a healthy lifestyle, which includes getting enough sleep, eating a balanced diet, exercising regularly, and managing chronic health concerns, can help to boost the immune system and lower the chance of infection.

How common is haemophilus influenzae

  • Every year, there are at least 3 million cases with serious disease and hundreds of thousands of deaths worldwide.

Is haemophilus influenzae contagious?

Yes, the disease is considered contagious and can be passed from person to person. When an infected person coughs or sneezes, bacteria can be transferred through respiratory droplets. Close contact with an infected individual, such as sharing personal things or living in the same household, might increase the risk of transmission.

Who are at risk of haemophilus influenzae

The risk factors for Haemophilus influenzae infections differ according to the kind of illness. Here are some persons who may be more vulnerable:

  • Infants and children, especially Children under the age of five, particularly those who have not been fully immunised against Haemophilus influenzae type b (Hib), are more likely to acquire severe illnesses, including meningitis.
  • Immunocompromised persons who have weak defence systems like HIV, undergoing chemotherapy, using immunosuppressants.
  • Geriatric people
  • People with specific medical disorders, such as chronic lung illness, chronic obstructive pulmonary disease (COPD), bronchiectasis, or heart disease, may be at a higher risk of Haemophilus influenzae respiratory tract infections.

When should I see a doctor?

If you suspect you have Haemophilus influenzae B symptoms like stiff neck and high fever in infants who become excessively crying, irritability, and high fever,  you should consult a doctor as soon as possible for correct diagnosis and treatment.


The bacteria Haemophilus influenzae causes a variety of illnesses in humans, including meningitis, pneumonia, and epiglottitis. It is divided into two forms: encapsulated and non-encapsulated, with encapsulated types producing severe disorders. Haemophilus 

can spread through respiratory droplets or the throat and nose, impacting multiple organs. The advent of the Hib vaccination has lowered the prevalence of severe infections, and antibiotics such as amoxicillin, ceftriaxone, and azithromycin are routinely used.


  1. Haemophilus influenzae Infections - Infections [Internet]. MSD Manual Consumer Version. Available from: https://www.msdmanuals.com/home/infections/bacterial-infections-gram-negative-bacteria/haemophilus-influenzae-infections
  2. Factsheet about Invasive Haemophilus influenzae disease [Internet]. European Centre for Disease Prevention and Control. Available from: https://www.ecdc.europa.eu/en/invasive-haemophilus-influenzae-disease/facts
  3. NHS Choices. Haemophilus influenzae type b (Hib) [Internet]. NHS. 2019. Available from: https://www.nhs.uk/conditions/hib/
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Asma Shaikh

Doctor of pharmacy - Done pharm-D from jinnah Sindh medical university Karachi pakistan

Im a pharm-D graduate has vast interest in biopharmaceutical and pharmacy practice with an Perfervid skill of writing combined with health sciences, she aims to continue her skills and interests in the future to contribute to breakthroughs in pharmaceutical industry.

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