Haemophilus influenzae is a bacterial pathogen that can cause a range of infections. It is a Gram-negative coccobacillus that primarily affects the respiratory tract but can also lead to invasive diseases such as meningitis, septicemia, and epiglottitis.
Haemophilus influenzae is classified into two major groups: encapsulated (typeable) and non-encapsulated (nontypeable). The encapsulated strains are further divided into six serotypes (a through f), with type b (Hib) being the most virulent and historically the leading cause of serious invasive disease. Non-encapsulated strains are often responsible for otitis media, sinusitis, and bronchitis.
This bacterium is typically spread through respiratory droplets when an infected person coughs or sneezes. Close contact, such as in daycare centers or among family members, facilitates transmission. Asymptomatic carriers can also spread the bacteria.
Risk factors include age (children under 5 and adults over 65), immunocompromised individuals, lack of vaccination, and those with underlying medical conditions such as COPD or asplenia.
Symptoms vary depending on the site of infection. Respiratory tract infections may present with cough, fever, and difficulty breathing, while invasive disease can lead to symptoms like high fever, stiff neck, headache, and altered mental status in the case of meningitis.
Diagnosis typically involves culturing the bacteria from sterile sites such as blood, cerebrospinal fluid, or pleural fluid. Polymerase chain reaction (PCR) methods and antigen detection tests are also used for more rapid diagnosis.
Treatment options include antibiotics such as amoxicillin, ceftriaxone, or azithromycin. The choice of antibiotic may depend on the severity of the infection and local resistance patterns.
The introduction of the Hib vaccine has significantly reduced the incidence of invasive Hib disease. Vaccination is recommended for all children and certain high-risk adults. Good hygiene practices and avoiding close contact with infected individuals can also help reduce transmission.
Before the widespread use of the Hib vaccine, Haemophilus influenzae type b was a leading cause of bacterial meningitis and other invasive diseases in children under 5 years. The incidence of invasive Hib disease has dramatically decreased in countries with high vaccination coverage. However, non-encapsulated strains and other serotypes continue to cause significant morbidity and mortality, particularly in older adults and immunocompromised individuals.
