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For Clinicians

Clinical Features

Disease caused by Haemophilus influenzae bacteria can affect many organ systems. The most common types of disease caused by Haemophilus influenzae type b (Hib) bacteria include pneumonia, bacteremia, meningitis, epiglottitis, septic arthritis, cellulitis, otitis media, purulent pericarditis, and other less common infections such as endocarditis and osteomyelitis. Non-b Haemophilus influenzae bacteria can cause disease similar to Hib infections. Nontypeable Haemophilus influenzae bacteria commonly causes ear infections in children and bronchitis in adults, but may also cause invasive disease, such as bacteremia and pneumonia.


3%-6% of Hib cases in children are fatal; up to 20% of patients who survive Hib meningitis have permanent hearing loss or other long-term neurological sequelae. Patients ≥65 years of age with invasive Haemphilus influenzae disease (Hib, non-b, and nontypeable) have higher case-fatality ratios (CFR) than children and young adults.

Key Resource

Hi Nm PCR Best Practices


Best Practices for Use of Polymerase Chain Reaction (PCR) for Diagnosing Haemophilus influenzae and Neisseria meningitidis Disease and Public Health Importance of Identifying Serotype/Serogroup


Etiologic Agent

Haemophilus influenzae is a pleomorphic gram-negative coccobacillus. H.influenzae may be either encapsulated (typeable) or unencapsulated (nontypeable). There are six encapsulated serotypes (designated a–f) that have distinct capsular polysaccharides.


Transmission occurs through direct contact with respiratory droplets from nasopharyngeal carrier or case patient. Neonates can acquire infection by aspiration of amniotic fluid or contact with genital tract secretions containing the bacteria.

Risk Groups

Unimmunized children younger than 4 years of age and household contacts and day-care classmates of a person with Hib disease are at increased risk of Hib disease. Increased risk for disease among close contacts of patients with non-b or nontypeable Haemophilus influenzae has not been identified. Patients with sickle cell disease, asplenia, HIV, certain immunodeficiency syndromes, and recipients of hematopoietic stem cell transplant and/or radiation therapy for malignant neoplasms are at increased risk for invasive Haemophilus influenzae disease. American Indian/Alaska Native populations are also at increased risk for invasive Haemophilus influenzae disease.


Due to routine use of the Hib conjugate vaccine since 1990, the incidence of Hib disease in infants and young children has decreased by 99% to fewer than 1 case per 100,000 children younger than 5 years of age. In the United States, Hib disease occurs primarily in underimmunized children and among infants too young to have completed the primary immunization series. 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.

The epidemiology of invasive H. influenzae disease in the United States has shifted since the introduction of the Hib vaccine. The largest burden of invasive H. influenzae disease now occurs in children <5 years of age and older adults ≥ 65 years of age. Nontypeable H. influenzae now causes the majority of invasive H. influenzae disease in all age groups. Between 2003-2012, the annual incidence of invasive nontypeable H. influenzae disease was 1.6 cases per 100,000 children younger than 5 years of age and 4.6 cases per 100,000 adults ≥ 65 years of age. Nontypeable H. influenzae also causes 30% to 52% of episodes of acute otitis media and sinusitis in children and is a common cause of recurrent otitis media.


Since licensure of conjugate vaccines for infants (1990) and children (1987), rates of Hib disease among children younger than five years old have declined by 99% in the United States, while rates for adults have remained stable. However, rates of disease among Alaska Natives remain higher than elsewhere in the United States. Nontypeable disease now causes the majority of invasive Haemophilus influenzae disease among all age groups in the United States.


For guidelines on treatment and chemoprophylaxis for invasive Hib disease, see the Red Book. Chemoprophylaxis is only recommended for Hib cases because disease among close contacts has not been identified with other types of Haemophilus influenzae bacteria.


Hib vaccine is one of the recommended routine childhood immunizations in the United States. Currently, three monovalent conjugate Hib vaccines and three combination vaccines that contain Hib conjugate are available. An infant primary series (2, 4, and 6 months of age or 2 and 4 months of age, depending on the vaccine type used) and a booster dose at 12 through 15 months of age is recommended. Please see the United States Childhood and Adolescent immunization schedule for more information. There are no vaccines for non-b and nontypeable Haemophilus influenzae bacteria.


All cases of Haemophilus influenzae (Hib, non-b, and nontypeable) should be reported to the Centers for Disease Control and Prevention (CDC) through the local or state public health department.


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