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H influenzae and other Haemophilus species may cause sinusitis, otitis, bronchitis, epiglottitis, pneumonia, cellulitis, arthritis, meningitis, and endocarditis. Nontypeable strains are responsible for most disease in adults. Alcohol use disorder, smoking, chronic lung disease, advanced age, and HIV infection are risk factors. Haemophilus species colonize the upper respiratory tract in patients with COPD and frequently cause purulent bronchitis.

Beta-lactamase–producing strains are less common in adults than in children. For adults with sinusitis, otitis, or respiratory tract infection, oral amoxicillin, 750 mg twice daily for 10–14 days, is adequate. For beta-lactamase–producing strains, use of the oral fixed-drug combination of amoxicillin, 875 mg, with clavulanate, 125 mg, is indicated. For the penicillin-allergic patient, oral cefuroxime axetil, 250 mg twice daily; or a fluoroquinolone (ciprofloxacin, 500 mg orally twice daily; levofloxacin, 500–750 mg orally once daily; or moxifloxacin, 400 mg orally once daily) for 7 days is effective. Azithromycin, 500 mg orally once followed by 250 mg daily for 4 days, is preferred over clarithromycin when a macrolide is the preferred agent. Trimethoprim-sulfamethoxazole (160/800 mg orally twice daily) can be considered, but resistance rates have been reported to be up to 25%.

In the more seriously ill patient (eg, the toxic patient with multilobar pneumonia), ceftriaxone, 1 g/day intravenously, is recommended pending determination of whether the infecting strain produces beta-lactamase. A fluoroquinolone (see above for dosages) can be used for the penicillin-allergic patients for a 10- to 14-day course of therapy.

Epiglottitis is characterized by an abrupt onset of high fever, drooling, and inability to handle secretions. An important clue to the diagnosis is complaint of a severe sore throat despite an unimpressive examination of the pharynx. Stridor and respiratory distress result from laryngeal obstruction. The diagnosis is best made by direct visualization of the cherry-red, swollen epiglottis at laryngoscopy. Because laryngoscopy may provoke laryngospasm and obstruction, especially in children, it should be performed in an intensive care unit or similar setting, and only at a time when intubation can be performed promptly. Ceftriaxone, 1 g intravenously every 24 hours for 7–10 days, is the drug of choice. Trimethoprim-sulfamethoxazole or a fluoroquinolone (see above for dosage) may be used in the patient with serious penicillin allergy.

Meningitis, rare in adults, is a consideration in the patient who has meningitis associated with sinusitis or otitis. Initial therapy for suspected H influenzae meningitis should be with ceftriaxone, 4 g/day in two divided doses, until the strain is proved not to produce beta-lactamase. Meningitis is treated for at least 7 days. Dexamethasone, 0.15 mg/kg intravenously every 6 hours, may reduce the incidence of long-term sequelae, principally hearing loss.

Brouwer  MC  et al. Epidemiology of community-acquired bacterial meningitis. Curr Opin Infect Dis. 2018;31:78.
[PubMed: 29176349]  
Langereis  JD  et al. Unraveling Haemophilus influenzae virulence mechanisms enable discovery of new targets for antimicrobials and vaccines. Curr Opin Infect Dis. 2020;33:231.
[PubMed: 32304471]  

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