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.
Diseases caused by Haemophilus species
H. influenzae causes many childhood infections, including meningitis Bacterial Meningitis in Infants Over 3 Months of Age Bacterial meningitis in infants is a serious infection of the meninges and subarachnoid space. Infants may present with nonspecific symptoms and signs (eg, lethargy, irritability, poor feeding... read more , bacteremia Bacteremia Bacteremia is the presence of bacteria in the bloodstream. It can occur spontaneously, during certain tissue infections, with use of indwelling genitourinary or IV catheters, or after dental... read more , septic arthritis Acute Infectious Arthritis Acute infectious arthritis is a joint infection that evolves over hours or days. The infection resides in synovial or periarticular tissues and is usually bacterial—in younger adults, frequently... read more , pneumonia Neonatal Pneumonia Neonatal pneumonia is lung infection in a neonate. Onset may be within hours of birth and part of a generalized sepsis syndrome or after 7 days and confined to the lungs. Signs may be limited... read more , tracheobronchitis Acute Bronchitis Acute bronchitis is inflammation of the tracheobronchial tree, commonly following an upper respiratory infection that occurs in patients without chronic lung disorders The cause is almost always... read more , otitis media Otitis Media (Acute) Acute otitis media is a bacterial or viral infection of the middle ear, usually accompanying an upper respiratory infection. Symptoms include otalgia, often with systemic symptoms (eg, fever... read more , conjunctivitis Neonatal Conjunctivitis Neonatal conjunctivitis is watery or purulent ocular drainage due to a chemical irritant or a pathogenic organism. Prevention with antigonococcal topical treatment at birth is routine. Diagnosis... read more , sinusitis Sinusitis Sinusitis is inflammation of the paranasal sinuses due to viral, bacterial, or fungal infections or allergic reactions. Symptoms include nasal obstruction and congestion, purulent rhinorrhea... read more , and acute epiglottitis Epiglottitis Epiglottitis is a rapidly progressive bacterial infection of the epiglottis and surrounding tissues that may lead to sudden respiratory obstruction and death. Symptoms include severe sore throat... read more . These infections, as well as endocarditis Infective Endocarditis Infective endocarditis is infection of the endocardium, usually with bacteria (commonly, streptococci or staphylococci) or fungi. It may cause fever, heart murmurs, petechiae, anemia, embolic... read more and urinary tract infections Urinary Tract Infection (UTI) in Children Urinary tract infection (UTI) is defined by ≥ 5 × 104 colonies/mL in a catheterized urine specimen or, in older children, by repeated voided specimens with ≥ 105 colonies/mL. In younger children... read more , 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 Chancroid Chancroid is infection of the genital skin or mucous membranes caused by Haemophilus ducreyi and characterized by papules, painful ulcers, and enlargement of the inguinal lymph nodes leading... read more . H. parainfluenzae and H. aphrophilus are rare causes of bacteremia, endocarditis, and brain abscess.
Diagnosis of Haemophilus Infections
Diagnosis of Haemophilus infections is by culture of blood and body fluids. Strains involved in invasive illness should be serotyped.
Treatment of Haemophilus Infections
Various antibiotics depending on site and severity of infection
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 Haemophilus influenzae Type b (Hib) Vaccine Haemophilus influenzae type b (Hib) vaccines help prevent Haemophilus infections but not infections caused by other strains of H. influenzae bacteria. H. influenzae causes many childhood infections... read more 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.
Prevention of Haemophilus Infections
Hib conjugate vaccines Haemophilus influenzae Type b (Hib) Vaccine Haemophilus influenzae type b (Hib) vaccines help prevent Haemophilus infections but not infections caused by other strains of H. influenzae bacteria. H. influenzae causes many childhood infections... read more 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.