Haemophilus Influenzae Infection

Droplet Precautions

H. influenzae can cause diseases in many organ systems but usually attacks the respiratory system. H. influenzae is one of the three most common organisms causing community-acquired pneumonia. It is also a common cause of epiglottiditis, laryngotracheobronchitis, bronchiolitis, otitis media, and meningitis. Less commonly, it causes bacterial endocarditis, conjunctivitis, facial cellulitis, septic arthritis, and osteomyelitis.

H. influenzae type b (Hib) infection predominantly affects children, at a rate of 3% to 5% in the United States. This incidence was higher before vaccinations were widely used. The Hib vaccine is administered to children at ages 2, 4, 6, and 15 months. In Native American and Alaska Native populations, the incidence of Hib infection exceeds 5%, possibly due to exposure, socioeconomic conditions, and/or genetic differences in immune response. Hib infection is fatal in 3% to 6% of cases; up to 20% of patients suffer permanent hearing loss or other long-term sequelae.

Causes

A small, gram-negative, pleomorphic aerobic bacillus, H. influenzae appears predominantly in coccobacillary exudates. It is usually found in the pharynx and, less commonly, in the conjunctiva and genitourinary tract. Transmission occurs by direct contact with nasopharyngeal secretions or respiratory droplets.

Complications

The microorganism can cause subdural effusions and permanent neurologic sequelae from meningitis; complete upper airway obstruction from epiglottiditis, cellulitis, and pericarditis; pleural effusion; and respiratory failure from pneumonia.

Assessment Findings

The patient may report a recent viral infection. Onset of H. influenzae infection is usually sudden with progressive symptoms. Generalized malaise is a common complaint, along with a high fever. H. influenzae provokes a characteristic tissue response—acute suppurative inflammation. When H. influenzae infects the larynx, trachea, or bronchial tree, it leads to irritable cough, dyspnea, mucosal edema, and thick, purulent exudate. When it invades the lungs, it causes bronchopneumonia. In the pharynx, H. influenzae usually produces no remarkable changes, except when it causes epiglottiditis, which generally affects both the laryngeal and pharyngeal surfaces. The pharyngeal mucosa may be reddened, rarely with a soft yellow exudate, although it usually appears normal or shows only slight diffuse redness, even while severe pain makes swallowing difficult or impossible. Meningitis, the most serious infection caused by H. influenzae, is indicated by fever and altered mental status. In young children, nuchal rigidity may be absent.

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