Many Haemophilus species are normal flora in the upper respiratory tract and rarely cause illness. Pathogenic strains enter the upper respiratory tract through droplet inhalation or direct contact. Spread is rapid in nonimmune populations. Children, particularly males, blacks, and Native Americans, are at highest risk of serious infection. Overcrowded living conditions and day care center attendance predispose to infection, as do immunodeficiency states, asplenia, and sickle cell disease.
There are several pathogenic species of Haemophilus; the most common is H. influenzae, which has 6 distinct encapsulated serotypes (a through f) and numerous nonencapsulated, nontypeable strains. Before the use of H. influenzae type b (Hib) conjugate vaccine, most cases of serious, invasive disease were caused by type b.
H. influenzae causes many childhood infections, including meningitis, bacteremia, septic arthritis, pneumonia, tracheobronchitis, otitis media, conjunctivitis, sinusitis, and acute epiglottitis. These infections, as well as endocarditis and urinary tract infections, may occur in adults, although far less commonly. These illnesses are discussed elsewhere in THE MANUAL.
Nontypeable H. influenzae strains cause mainly mucosal infections (eg, otitis media, sinusitis, conjunctivitis, bronchitis). Occasionally, nonencapsulated strains cause invasive infections in children, but they may cause up to half of serious H. influenzae infections in adults.
H. influenzae biogroup aegyptius (formerly called H. aegyptius) may cause mucopurulent conjunctivitis and bacteremic Brazilian purpuric fever. H. ducreyi causes chancroid. H. parainfluenzae and H. aphrophilus are rare causes of bacteremia, endocarditis, and brain abscess.
Treatment of Haemophilus infections depends on nature and location of the infection, but, for invasive disease, beta-lactam/beta-lactamase inhibitors, fluoroquinolones, and 2nd- and 3rd-generation cephalosporins are used. The Hib conjugate vaccine has markedly reduced the rate of bacteremia.
Children with serious illness are hospitalized with contact and respiratory isolation for 24 hours after starting antibiotics.
Antibiotic choices depend strongly on the site of infection and require susceptibility testing; many isolates in the US produce beta-lactamase (eg, > 50% are resistant to ampicillin).
For invasive illness, including meningitis, cefotaxime or ceftriaxone is recommended. For less serious infections, oral cephalosporins (except for 1st-generation cephalosporins such as cephalexin), azithromycin or other macrolides, and amoxicillin/clavulanate are generally effective. (See individual disease entries for specific recommendations.)
Cefotaxime and ceftriaxone eliminate respiratory carriage of H. influenzae, but other antibiotics used for systemic infection do not do so reliably. Thus, children with systemic infection who were not treated with cefotaxime or ceftriaxone should be given rifampin immediately after completing treatment and before resuming contact with other children.
Hib conjugate vaccines are available for children ≥ 2 months of age and have reduced invasive infections (eg, meningitis, epiglottitis, bacteremia) by 99%. A primary series is given at age 2, 4, and 6 months or at age 2 and 4 months, depending on the vaccine product. A booster at age 12 to 15 months is indicated.
Contacts within the household may have asymptomatic H. influenzae carriage. Unimmunized or incompletely immunized household contacts < 4 years are at risk of illness and should receive a dose of vaccine. In addition, all household members (except pregnant women) should receive prophylaxis with oral rifampin 600 mg (20 mg/kg for children ≥ 1 month;10 mg/kg for children < 1 month) once a day for 4 days.
Nursery or day care contacts should receive prophylaxis if ≥ 2 cases of invasive disease occurred in 60 days. The benefit of prophylaxis if only one case occurred has not been established.
Several species of Haemophilus are pathogenic; the most common is H. influenzae.
H. influenzae causes many types of mucosal and, less commonly, invasive infection, primarily in children.
Antibiotic choices depend strongly on the site of infection and require susceptibility testing.
H. influenzae type b (Hib) conjugate vaccines, given as part of routine childhood immunization to children ≥ 2 months, have reduced invasive infections by 99%.
Close contacts may be asymptomatic H. influenzae carriers and typically are given prophylaxis with rifampin.