Haemophilus Influenzae Infections Clinical Presentation

Updated: Aug 30, 2023
  • Author: Joseph Adrian L Buensalido, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Meningitis is the most serious manifestation of H influenzae type b (Hib) infection. Symptoms of antecedent URTI are common. Altered mental status and fever are the most common presenting features. Headache and photophobia are usually present in older children.

Symptoms related to other infectious foci (eg, cellulitis, arthritis, pneumonia) are encountered in 10-20% of children. Infants have nonspecific symptoms, including irritability, fever, lethargy, poor feeding, and vomiting.

H influenzae accounts for 5-10% cases of adult meningitis, and patients can present with at least one of the classic triad of fever, neck stiffness, and altered mental status.


The buccal and periorbital regions are most commonly involved with associated fever. Orbital cellulitis is uncommon and tends to be a complication of ethmoid or sphenoid sinusitis.


Patients with H influenzae epiglottitis may have respiratory difficulty (78%), sore throat (65%), history of fever (57%), difficulty swallowing (49%), drooling (42%), change in voice (33%) and cough (19%). [41]


H influenzae pneumonia is clinically indistinguishable from other bacterial pneumonias, but insidious onset and a history of fever, cough, and purulent sputum production are usually noted.

H influenzae was shown to be more common as a cause of community-acquired pneumonia (CAP) in patients with previous pneumococcal vaccination and those with respiratory co-morbidities. [42]


Patients with Hib pericarditis present with a history of fever, respiratory distress, and tachycardia.

Septic arthritis

Patients with H influenzae septic arthritis note joint pain, swelling, and decreased mobility.

Occult bacteremia

Fever, anorexia, and lethargy occur in persons with occult bacteremia.

Underlying medical conditions

Pulmonary disease, HIV infection (and other immunodeficiency states), alcoholism, pregnancy, and malignancy may predominate in adults with invasive Hib disease.

Patients with primary ciliary dyskinesia, an inherited condition with motile cilia dysfunction, have been shown to grow H influenzae from sputum and nasal lavage. More recently, these same patients appear to be susceptible to the development of NTHi biofilm, as seen in both culture and confocal and scanning microscopy. [43, 44]

NTHi is considered a common commensal in the nasopharynx, but when it reaches the lower respiratory tree in patients with COPD, it is associated with significant inflammation that generally leads to morbidity due to worsening symptoms and more frequent COPD exacerbations. [45, 46]

Neonatal infections

Neonates with H influenzae disease present within 24 hours of birth; these infections are caused by NTHi strains, which colonize the maternal genital tract.

Premature birth, premature rupture of membranes, low birth weight, and maternal chorioamnionitis are associated with H influenzae disease.

Manifestations may be nonspecific and may include those of bacteremia, sepsis, meningitis, pneumonia, respiratory distress, scalp abscess, conjunctivitis, and vesicular eruption.

NTHi is a major cause of pneumonia in infants in developing countries.

Nonencapsulated H influenzae infections

Nonencapsulated H influenzae commonly causes various mucosal infections, including otitis media and conjunctivitis.

S pneumoniae and nonencapsulated H influenzae are the most common causes of otitis media, which manifests in infants as fever and irritability and in older patients as ear pain. Frequently, a history of URTI exists.

NTHi is a major cause of conjunctivitis in older children and can cause outbreaks, especially in daycare centers. After S pneumoniae, NTHi is the most common cause of community-acquired bacterial pneumonia in adults. It is common in patients with COPD and HIV disease and exacerbates COPD, symptoms of which include low-grade fever, increased cough and sputum production, and dyspnea. NTHi invasive disease is frequently associated with underlying medical conditions, including prematurity, advanced age, alcoholism, malignancy, CF, asthma, cerebrospinal fluid (CSF) leak, CNS shunts, congenital heart disease, and immunoglobulin deficiency.




Clinical manifestations of Hib meningitis are indistinguishable from other causes of bacterial meningitis.

The usual presentation consists of a few days of mild illness followed by ominous deterioration.

Altered mental status and fever are the most common findings.

Seizures and coma develop as the disease progresses.

Children may have few specific signs. Nuchal rigidity is often absent in children younger than 18 months. In infants, the disease course may be fulminant, with death occurring within a few hours.

Consider the possibility of subdural effusion, a common complication of Hib meningitis, in a patient who has been treated for 3 days with appropriate antibiotics and has experienced a tense anterior fontanelle, seizures (especially if focal), hemiparesis, or altered CNS function.


The clinical features are fever and a raised, indurated, tender area with indistinct margins mostly on the head and neck, particularly the buccal and preseptal areas. This is often caused by contiguous sinus disease. The indurated area may progress to a violaceous hue, although this is not specific to Hib.

Orbital cellulitis may occur and is distinguished from periorbital cellulitis based on the presence of proptosis, chemosis, impaired vision, limitation of extraocular movements, and pain with eye movement. A secondary focus of infection, including meningitis, is evident in 10-15% of patients with orbital cellulitis.


Clinical manifestations in children include a toxic anxious appearance, progressive respiratory difficulty, and the inability to swallow secretions while sitting in the tripod position (ie, sitting with arms back, trunk leaning forward, neck hyperextended and chin forward in an attempt to open the airway fully).

Physical examination findings include change in voice (90%), stridor (81%), neck tenderness (65%), pharyngitis (61%), and adenopathy (39%). [41]


H influenzae pneumonia (whether Hib or NTHi) is clinically indistinguishable from other bacterial pneumonias.


The individual is acutely ill with fever and respiratory distress.

Septic arthritis

Hib septic arthritis affects single large joints (eg, knee, ankle, hip, elbow).

Symptoms, usually preceded by a URTI, include decreased range of motion, erythema, and warmth and swelling in affected joints, in addition to fever.

In adults, joint involvement can be monoarticular or polyarticular.

Extra-articular sites of infection, including those associated with meningitis, pneumonia, cellulitis, and sinusitis, may also be evident.

Occult bacteremia

Occult bacteremia is characterized by fever (temperature >39°C) with no obvious focus of infection. About 30-50% of patients have focal infections.


Nonencapsulated H influenzae infections can manifest in various mucosal infections (eg, otitis media, conjunctivitis, sinusitis, bronchitis). An otitis media diagnosis is confirmed with pneumatic otoscopy. Conjunctivitis usually is bilateral and characterized by conjunctival hyperemia and purulent eye discharge.

NTHi strains can cause postpartum sepsis with ​endometritis, tuboovarian abscess, and chronic salpingitis.

Signs of invasive disease in neonates include sepsis, pneumonia, conjunctivitis, respiratory distress syndrome, scalp abscess, cellulitis, meningitis, congenital vesicular eruption, mastoiditis, and septic arthritis.



Bacteremia precedes Hib meningitis and other invasive Hib diseases. Direct extension of infection from the sinuses or ears is rare. The magnitude and duration of bacteremia are the primary determinants of CNS invasion, which occurs via the choroid plexus. The magnitude of the CSF bacterial density correlates with the severity of the disease. Morbidity and mortality associated with meningitis result from inflammation, edema, and increased CSF pressure. Brain parenchymal invasion is rare.

In epiglottitis, Hib invades the epiglottis and supraglottic tissues, causing cellulitis and swelling that causes the epiglottis to curl posteriorly and inferiorly over the airway, thus obstructing airflow during inspiration but allowing normal expiration. An acute airway obstruction follows.

Invasive H influenzae disease in neonates is rare and is caused most often by NTHi strains. This condition is associated with premature birth, premature rupture of membranes, low birth weight, and maternal chorioamnionitis. Transmission occurs through the maternal genital tract. NTHi biotype 4 can colonize the genital tract and is a major cause of invasive disease.



Complications of meningitis include seizures, cerebral edema, subdural effusion or empyema, inappropriate secretion of antidiuretic hormone syndrome, cortical infarction, cerebritis, intracerebral abscess, hydrocephalus, and cerebral herniation. Protracted fever is not uncommon, with approximately 10% of children remaining febrile for at least 10 days.

Complications of orbital cellulitis include subperiosteal or orbital abscesses.

Complications of pneumonia include empyema and pericarditis.

Complications of otitis and sinusitis include mastoiditis and parameningeal abscess.