Haemophilus influenzae: Infections, Symptoms & Vaccine
Haemophilus influenzae is a bacterium that can cause serious infections such as pneumonia, meningitis, and ear infections. Type b (Hib) is especially dangerous for infants and young children.
Things worth knowing about "Haemophilus influenzae"
Haemophilus influenzae is a bacterium that can cause serious infections such as pneumonia, meningitis, and ear infections. Type b (Hib) is especially dangerous for infants and young children.
What is Haemophilus influenzae?
Haemophilus influenzae is a gram-negative, non-motile coccobacillus (a small rod-shaped bacterium) that exclusively colonizes humans. Despite its name, this bacterium has no connection to the influenza virus. The misleading name dates back to the 1918 influenza pandemic, when the bacterium was mistakenly believed to be the cause of the flu. Haemophilus influenzae exists in two main forms: encapsulated strains (serotypes a through f) and unencapsulated, non-typeable strains (NTHi).
Occurrence and Transmission
The bacterium naturally colonizes the nasopharynx (throat and nasal passages) of many healthy individuals without causing symptoms. It is transmitted through:
- Droplet infection during coughing, sneezing, or speaking
- Direct contact with secretions from an infected person
Those at highest risk include infants, young children, the elderly, and individuals with a weakened immune system.
Diseases and Symptoms
Depending on the serotype and the health status of the individual, Haemophilus influenzae can cause a wide range of conditions:
Invasive Infections (primarily type b, Hib)
- Meningitis (inflammation of the membranes surrounding the brain): high fever, severe headache, neck stiffness, sensitivity to light
- Epiglottitis (inflammation of the epiglottis): difficulty swallowing, drooling, and breathing difficulties – a medical emergency
- Pneumonia (lung infection): cough, fever, difficulty breathing
- Septic arthritis (joint infection), osteomyelitis (bone infection), and sepsis (bloodstream infection)
Non-Invasive Infections (primarily non-typeable strains, NTHi)
- Otitis media (middle ear infection): very common in young children
- Sinusitis (sinus infection)
- Acute bronchitis, particularly in patients with chronic obstructive pulmonary disease (COPD)
- Conjunctivitis (pink eye)
Diagnosis
The diagnosis of a Haemophilus influenzae infection is established through:
- Bacterial culture: growing the organism from blood, cerebrospinal fluid, sputum, or swabs
- PCR testing (polymerase chain reaction): rapid detection of bacterial genetic material
- Antigen detection in cerebrospinal fluid or urine for suspected invasive infections
- Antibiogram: testing antibiotic susceptibility, as resistance (especially to ampicillin via beta-lactamase production) is common
Treatment
Treatment depends on the severity of the infection and the antibiotic resistance profile of the strain:
- Mild to moderate infections (e.g., otitis media, sinusitis): oral antibiotics such as amoxicillin-clavulanate or cephalosporins
- Severe and invasive infections (e.g., meningitis, epiglottitis): intravenous third-generation cephalosporins (e.g., ceftriaxone or cefotaxime)
- In cases of meningitis, dexamethasone (a corticosteroid) is often added to reduce inflammation and minimize long-term complications
Vaccination and Prevention
A highly effective vaccine is available against Haemophilus influenzae type b (Hib). Health authorities worldwide, including the World Health Organization (WHO) and national immunization programs, recommend Hib vaccination for all infants as part of the standard childhood immunization schedule. Since the introduction of the vaccine, invasive Hib disease has declined dramatically. However, the Hib vaccine does not protect against infections caused by non-typeable strains (NTHi).
References
- World Health Organization (WHO): Haemophilus influenzae type b (Hib) vaccination position paper. Weekly Epidemiological Record, 2013.
- Watt, J. P. et al. - Haemophilus influenzae type b disease worldwide. In: The Lancet Infectious Diseases, 2009.
- Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th edition. Elsevier, 2020.
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