Clinical Overview of Haemophilus influenzae Disease

Key points

  • Haemophilus influenzae can cause infections ranging from minor to serious, even deadly.
  • Chemoprophylaxis and vaccination are recommended to prevent one type of H. influenzae disease — type b or Hib.
  • While other types of H. influenzae disease are uncommon, they've been increasing in recent years.
Healthcare provider observing an x-ray of the chest.

Cause

An image of Haemophilus influenzae that was generated by a computer based on scanning electron microscopic imagery.
This image of Haemophilus influenzae was computer generated.

H. influenzae are gram-negative bacteria. They can be encapsulated (typeable) or unencapsulated (nontypeable). The 6 encapsulated serotypes are designated a through f (e.g., Hia, Hib).

Types

H. influenzae infections can affect many organ systems.

Typeable H. influenzae

The most common types of infections caused by typeable H. influenzae, including Hib, include:

  • Pneumonia
  • Bacteremia
  • Meningitis
  • Epiglottitis
  • Septic arthritis
  • Cellulitis
  • Otitis media
  • Purulent pericarditis

Less common infections include endocarditis and osteomyelitis.

Nontypeable H. influenzae

Nontypeable H. influenzae commonly cause acute otitis media and sinusitis episodes in children. They commonly cause bronchitis in adults.

Nontypeable H. influenzae can also cause invasive disease in all ages.

Risk factors

The following groups are at increased risk of invasive H. influenzae disease:

  • Children younger than 5 years of age
  • Adults 65 years or older
  • American Indian and Alaska Native people

Certain medical conditions can also increase someone's risk of H. influenzae disease:

  • Asplenia
  • HIV infection
  • Immunoglobulin and complement component deficiencies
  • Malignant neoplasms requiring hematopoietic stem cell transplant, chemotherapy, or radiation therapy
  • Sickle cell disease

Hib disease specifically

The following groups are at increased risk of Hib disease:

  • Daycare classmates of someone with Hib disease
  • Household contacts of someone with Hib disease
  • Unimmunized and underimmunized children younger than 5 years old

How it spreads

Transmission usually occurs when someone breathes in or has direct contact with respiratory droplets containing the bacteria. Like symptomatic people, nasopharyngeal carriers can spread the bacteria by coughing and sneezing.

Neonates can acquire infection by aspiration of infected amniotic fluid or through contact with genital tract secretions containing the bacteria.

Prevention

Chemoprophylaxis

CDC recommends chemoprophylaxis for close contacts of Hib cases. CDC doesn't have similar guidelines for other types of H. influenzae disease.

Findings: Non-type b secondary transmission likely‎

Be aware of the possibility of secondary cases following contact with someone with invasive H. influenzae disease, regardless of type. This is especially true for people with certain medical conditions.

Vaccination

Hib vaccine is a routine U.S. childhood vaccination.

There are no vaccines for non-b and nontypeable H. influenzae disease.

Diagnosis

Diagnosis of invasive disease caused by H. influenzae is based on clinical presentation and laboratory tests. These tests can include culture and nucleic acid amplification by a validated assay (e.g., polymerase chain reaction [PCR]).

Advantages and disadvantages of culture and PCR‎

Culture and PCR have advantages and disadvantages when diagnosing H. influenzae disease. Serotype information informs public health response and helps identify outbreaks.

Treatment and recovery

For treatment guidelines, see the H. influenzae chapter of the Red Book.

Complications

Between 3% to 6% of Hib cases in children are fatal.

People 65 years or older with invasive H. influenzae disease 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.

Trends and surveillance

Hib disease is no longer common.

Invasive H. influenzae disease is a reportable condition in the United States.