Disease caused by Haemophilus influenzae can affect many organ systems. The most common types of disease caused by H. influenzae type b (Hib) include pneumonia, bacteremia, meningitis, epiglottitis, septic arthritis, cellulitis, otitis media, and purulent pericarditis. Less common infections include endocarditis and osteomyelitis. Non-b H. influenzae can cause disease similar to Hib infections. Nontypeable H. influenzae commonly causes ear infections in children and bronchitis in adults, but can cause invasive disease.
H. influenzae is a pleomorphic gram-negative coccobacillus. H. influenzae may be either encapsulated (typeable) or unencapsulated (nontypeable). There are six encapsulated serotypes (designated a through f) that have distinct capsular polysaccharides.
Between 3% to 6% of Hib cases in children are fatal. Patients ≥65 years of age with invasive H. influenzae disease (Hib, non-b, and nontypeable) have higher case-fatality ratios than children. Up to 20% of patients who survive Hib meningitis have permanent hearing loss or other long-term neurological sequelae.
Transmission occurs through direct contact with respiratory droplets from a nasopharyngeal carrier or case patient. Neonates can acquire infection by aspiration of amniotic fluid or contact with genital tract secretions containing the bacteria.
The following groups are at increased risk of Hib disease:
- Unimmunized children younger than 5 years of age
- Household contacts of a person with Hib disease
- Daycare classmates of a person with Hib disease
In addition, the following groups are at increased risk of H. influenzae disease:
- Children younger than 5 years of age
- Adults 65 years or older
- American Indians and Alaska Natives
- People with any of the following medical conditions
- Sickle cell disease
- Immunoglobulin and complement component deficiencies
- Malignant neoplasms requiring hematopoietic stem cell transplant, chemotherapy, or radiation therapy
The epidemiology of invasive H. influenzae disease in the United States has shifted since the introduction of the Hib vaccine. The United States began using Hib vaccine for children in 1987 and for infants in 1990. Since then, the annual incidence of invasive Hib disease in children aged younger than 5 years old decreased by 99%. Now, nontypeable H. influenzae causes the majority of invasive H. influenzae disease among all age groups in the United States. In addition:
- Rates of Hib disease remain stable among adults
- Rates of Hib disease remain higher among Alaska Natives than for other races
In developing countries, where routine vaccination with Hib vaccine is not widely available, Hib remains a major cause of lower respiratory tract infections in infants and children.
In the United States, Hib disease is not common. In 2015, the incidence of invasive Hib disease was 0.08 cases per 100,000 in children younger than 5 years of age. It occurs primarily in underimmunized children and in infants too young to have completed the primary immunization series.
In 2015, the incidence of non-b H. influenzae invasive disease was 1.3 per 100,000 in children younger than 5 years of age.
Nontypeable H. influenzae now causes the majority of invasive H. influenzae disease in all age groups. In 2015, the incidence of invasive nontypeable H. influenzae disease was
- 7 cases per 100,000 in children younger than 5 years of age
- 2 cases per 100,000 in adults 65 years of age and older
Nontypeable H. influenzae also causes 30% to 52% of episodes of acute otitis media and sinusitis in children. It can be a common cause of recurrent otitis media.
For guidelines on treatment and chemoprophylaxis for invasive Hib disease, see the Red BookExternal. CDC recommends chemoprophylaxis for close contacts of Hib cases, but does not have guidelines for other types of H. influenzae disease.
Hib vaccine is one of the recommended routine childhood immunizations in the United States. Learn more:
- Hib Vaccine Recommendations
- About Hib Vaccines
- Storage and Handling for Hib Vaccines
- Administering Hib Vaccines
- Hib Vaccine Resources
There are no vaccines for non-b and nontypeable H. influenzae.
Invasive H. influenzae (Hib, non-b, and nontypeable) is a reportable condition in all states. Clinicians should report all cases to CDC through the local or state public health department.
- Briere EC. Food and Drug Administration approval for use of Hiberix as a 3-dose primary Haemophilus influenzae type b (Hib) vaccination series. MMWR Morb Mortal Wkly Rep. 2016;65(16):418–419.
- Briere EC, Rubin L, Moro PL, Cohn A, Clark T, Messonnier N. Prevention and control of Haemophilus influenzae type b disease: Recommendations of the Advisory Committee on Immunization Practices (ACIP).. MMWR Morb Mortal Wkly Rep. 2014;63(RR01):1–14.
- Blain A, MacNeil, J, Wang X, et al. Invasive Haemophilus influenzae disease in adults ≥65 years, United States, 2011External. Open Forum Infect Dis. 2014;1(2): ofu044.
- MacNeil JR, Cohn AC, Farley M, et al. Current epidemiology and trends in invasive Haemophilus influenzae disease—United States, 1989–2008External. Clin Infect Dis. 2011;53:1230–6.
- Rubach MP, Bender JM, Mottice S, et al. Increasing incidence of invasive Haemophilus influenzae disease in adults, Utah, USA.. Emerg Infect Dis.. 2011;17:1645–50.