Meningitis (Haemophilus influenzae type b - Hib)
Overview
Plain-Language Overview
Meningitis caused by Haemophilus influenzae type b (Hib) is an infection that affects the protective membranes covering the brain and spinal cord, called the meninges. This condition primarily impacts the central nervous system and can cause symptoms such as fever, headache, neck stiffness, and confusion. It is a serious illness that can lead to complications like hearing loss or brain damage if not treated promptly. The infection is caused by the bacteria Haemophilus influenzae type b, which mainly affects young children. Early recognition and diagnosis are crucial because the infection can progress rapidly and affect overall health significantly.
Clinical Definition
Meningitis (Haemophilus influenzae type b - Hib) is an acute inflammation of the meninges caused by the encapsulated gram-negative bacterium Haemophilus influenzae type b. It primarily affects infants and young children, leading to a severe bacterial infection of the central nervous system. The pathogenesis involves bacterial invasion of the bloodstream followed by crossing the blood-brain barrier, resulting in meningeal inflammation, increased intracranial pressure, and potential neuronal injury. Clinically, it presents with fever, neck stiffness, altered mental status, and sometimes seizures. The disease is significant due to its rapid progression and high risk of serious complications such as hearing loss, neurological deficits, and death if untreated. Vaccination against Hib has dramatically reduced incidence but it remains a critical diagnosis in unvaccinated populations.
Inciting Event
Nasopharyngeal colonization by Hib precedes invasive disease.
Upper respiratory tract infection may facilitate mucosal invasion.
Bacteremia allows hematogenous spread to the meninges.
Breakdown of mucosal barriers due to viral infections can trigger invasion.
Latency Period
Symptom onset typically occurs within 1-3 days after bacterial invasion.
Rapid progression from colonization to meningitis can occur over hours to days.
Incubation period is short, often less than a week from exposure to symptoms.
Diagnostic Delay
Early symptoms mimic viral infections, leading to misdiagnosis.
Non-specific initial signs such as fever and irritability delay suspicion.
Lack of vaccination history awareness may delay consideration of Hib.
Prior antibiotic use can reduce culture yield, complicating diagnosis.
Clinical Presentation
Signs & Symptoms
High fever and headache are hallmark symptoms in older children and adults.
Vomiting and photophobia commonly accompany meningeal irritation.
Irritability and poor feeding are typical in infants.
Seizures may occur due to cortical irritation or complications.
Neck stiffness is a classic sign of meningeal inflammation.
History of Present Illness
Acute onset of high fever and irritability is typical.
Headache, vomiting, and photophobia develop as meningeal inflammation progresses.
Neck stiffness and altered mental status indicate worsening disease.
Seizures may occur in severe cases due to increased intracranial pressure.
Past Medical History
Incomplete or absent Hib vaccination is a key factor.
Recent upper respiratory infections may precede meningitis onset.
History of immunodeficiency or complement deficiency increases risk.
Exposure to daycare or crowded environments is relevant.
Family History
No specific familial syndromes are associated with Hib meningitis.
Family members may share exposure risks in household outbreaks.
Inherited complement deficiencies can predispose to recurrent infections.
Physical Exam Findings
Fever and lethargy are common in infants and young children with Hib meningitis.
Nuchal rigidity indicating meningeal inflammation is frequently observed.
Bulging fontanelle may be present in infants due to increased intracranial pressure.
Petechial or purpuric rash can occasionally be seen in invasive Hib infection.
Altered mental status ranging from irritability to coma may be evident.
Diagnostic Workup
Diagnostic Criteria
Diagnosis of meningitis caused by Haemophilus influenzae type b is established by lumbar puncture with cerebrospinal fluid (CSF) analysis showing pleocytosis, elevated protein, and decreased glucose. Identification of the organism is confirmed by CSF Gram stain and culture, which reveal gram-negative coccobacilli. Rapid diagnosis can be aided by polymerase chain reaction (PCR) testing for Hib DNA in CSF. Blood cultures may also be positive. Clinical presentation combined with these laboratory findings confirms the diagnosis.
Pathophysiology
Key Mechanisms
Colonization of the nasopharynx by Haemophilus influenzae type b (Hib) precedes invasion.
Capsular polysaccharide (PRP) evades phagocytosis, allowing bloodstream invasion.
Bacterial invasion of the meninges triggers a robust inflammatory response.
Release of proinflammatory cytokines increases blood-brain barrier permeability.
Neutrophil infiltration and edema cause increased intracranial pressure and neuronal injury.
| Involvement | Details |
|---|---|
| Organs | Brain is affected by inflammation and edema, which can cause increased intracranial pressure and neurological deficits. |
Blood vessels in the central nervous system become permeable, facilitating immune cell infiltration and contributing to cerebral edema. | |
| Tissues | Meninges are inflamed in Hib meningitis, leading to characteristic symptoms such as neck stiffness and photophobia. |
Choroid plexus tissue may be involved in the inflammatory process, affecting cerebrospinal fluid production and composition. | |
| Cells | Neutrophils are the primary immune cells infiltrating the cerebrospinal fluid, mediating bacterial clearance and inflammation. |
Macrophages participate in phagocytosis of bacteria and release of pro-inflammatory cytokines in the meninges. | |
Endothelial cells of the blood-brain barrier become activated and contribute to increased permeability during infection. | |
| Chemical Mediators | Tumor necrosis factor-alpha (TNF-α) promotes inflammation and recruitment of immune cells to the meninges. |
Interleukin-1 beta (IL-1β) enhances vascular permeability and fever response in bacterial meningitis. | |
Prostaglandins mediate vasodilation and contribute to meningeal inflammation and headache. |
Treatments
Pharmacological Treatments
Ceftriaxone
- Mechanism:
Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins, leading to cell lysis.
- Side effects:
Allergic reactions
Biliary sludge
Diarrhea
- Clinical role:
First-line
Ampicillin
- Mechanism:
Binds to penicillin-binding proteins and inhibits bacterial cell wall synthesis, effective against Haemophilus influenzae strains producing beta-lactamase.
- Side effects:
Hypersensitivity reactions
Rash
Diarrhea
- Clinical role:
First-line
Dexamethasone
- Mechanism:
Reduces meningeal inflammation and cerebral edema by inhibiting pro-inflammatory cytokine production.
- Side effects:
Hyperglycemia
Immunosuppression
Gastrointestinal bleeding
- Clinical role:
Adjunctive
Non-pharmacological Treatments
Supportive care including maintenance of airway, breathing, and circulation to prevent hypoxia and shock.
Intravenous fluid management to maintain hydration and electrolyte balance.
Close neurological monitoring for signs of increased intracranial pressure or seizures.
Prevention
Pharmacological Prevention
Hib conjugate vaccine is the primary pharmacological prevention against invasive Hib disease.
Rifampin prophylaxis is recommended for close contacts to prevent secondary cases.
Empiric antibiotic therapy with third-generation cephalosporins is critical for treatment and prevention of complications.
Non-pharmacological Prevention
Routine childhood immunization schedules including Hib vaccine reduce disease incidence.
Good hand hygiene and respiratory etiquette limit transmission of Haemophilus influenzae.
Avoidance of tobacco smoke exposure decreases mucosal colonization risk.
Screening and prompt treatment of otitis media can prevent progression to meningitis.
Isolation of infected individuals during acute illness reduces spread.
Outcome & Complications
Complications
Hydrocephalus from impaired CSF absorption is a serious complication.
Seizures and status epilepticus may develop during acute illness.
Subdural effusions or empyema can occur as localized infections.
Septic shock and disseminated intravascular coagulation may result from systemic spread.
Cerebral infarction due to vasculitis or thrombosis is possible.
| Short-term Sequelae | Long-term Sequelae |
|---|---|
|
|
Differential Diagnoses
Meningitis (Haemophilus influenzae type b - Hib) versus Neisseria meningitidis meningitis
Meningitis (Haemophilus influenzae type b - Hib) | Neisseria meningitidis meningitis |
|---|---|
Haemophilus influenzae type b is a gram-negative coccobacillus | Neisseria meningitidis is a gram-negative diplococcus |
Primarily affects infants and young children under 5 years | Commonly affects older children and adolescents |
More common in unvaccinated children with no specific outbreak exposure | Often associated with outbreaks in close-contact settings like dormitories |
Responds to third-generation cephalosporins; prophylaxis also recommended for close contacts | Responds well to third-generation cephalosporins and may require prophylaxis for contacts |
Meningitis (Haemophilus influenzae type b - Hib) versus Streptococcus pneumoniae meningitis
Meningitis (Haemophilus influenzae type b - Hib) | Streptococcus pneumoniae meningitis |
|---|---|
Haemophilus influenzae type b is a gram-negative coccobacillus | Streptococcus pneumoniae is a gram-positive lancet-shaped diplococcus |
Primarily affects infants and young children | Common in all age groups, especially adults and elderly |
CSF shows high neutrophils, low glucose, and positive gram stain for gram-negative coccobacilli | CSF shows high neutrophils, low glucose, and positive gram stain for gram-positive cocci |
Incidence reduced by Hib conjugate vaccine | Incidence reduced by pneumococcal conjugate vaccine |
Meningitis (Haemophilus influenzae type b - Hib) versus Viral meningitis
Meningitis (Haemophilus influenzae type b - Hib) | Viral meningitis |
|---|---|
CSF shows neutrophilic predominance, low glucose, and elevated protein | CSF shows lymphocytic predominance, normal glucose, and mildly elevated protein |
Often severe with rapid progression and higher risk of complications | Usually self-limited with milder symptoms and better prognosis |
CSF culture or antigen test positive for Haemophilus influenzae type b | PCR positive for viral nucleic acids in CSF |
Meningitis (Haemophilus influenzae type b - Hib) versus Tuberculous meningitis
Meningitis (Haemophilus influenzae type b - Hib) | Tuberculous meningitis |
|---|---|
Acute onset with rapid progression over hours to days | Subacute to chronic progression over weeks with gradual symptom onset |
CSF shows neutrophilic predominance, elevated protein, and low glucose | CSF shows lymphocytic predominance, very high protein, and low glucose |
Positive culture or antigen test for Haemophilus influenzae type b | Positive acid-fast bacilli stain or PCR for Mycobacterium tuberculosis in CSF |
Meningitis (Haemophilus influenzae type b - Hib) versus Listeria monocytogenes meningitis
Meningitis (Haemophilus influenzae type b - Hib) | Listeria monocytogenes meningitis |
|---|---|
Primarily affects young children and infants | Common in neonates, elderly, and immunocompromised adults |
Haemophilus influenzae type b is a gram-negative coccobacillus | Listeria monocytogenes is a gram-positive rod |
Treated effectively with third-generation cephalosporins | Requires ampicillin or penicillin; resistant to cephalosporins |