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Epidemiology

Reporting Obligations

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Aetiologic Agent

Haemophilus influenzae (Hi) is a gram-negative encapsulated coccobacilli bacterium that causes invasive disease and illness. H. influenzae strains are either encapsulated (typeable) or non-encapsulated (non-typeable). Encapsulated strains (classified as serotypes a to f), are more likely to cause invasive disease than non-encapsulated strains. All strains resulting in invasive disease are reportable.

Non-b H. influenzae now accounts for the majority of invasive H. influenzae disease in Canada.

Clinical Presentation

H. influenzae disease in humans ranges from non-invasive infections such as acute otitis media to severe invasive infections such as meningitis and epiglottitis. Haemophilus influenzae serotype b (Hib) is the most pathogenic strain, causing 95% of invasive disease prior to the introduction of vaccine programs. Other common types of invasive disease include epiglottitis, pneumonia, arthritis and cellulitis. Non-type b encapsulated strains (a, c-f) can also cause invasive disease similar to type b infections. In the pre-vaccine era, the most common presentation of invasive disease was meningitis (50%–65% of cases).

Non-typeable strains may cause invasive disease but are generally less virulent than encapsulated strains. Non-typeable strains more commonly cause infections such as conjunctivitis, otitis media, sinusitis, and pneumonia.

Modes of Transmission

Transmission is person-to-person, most commonly by inhalation of respiratory tract droplets or by direct contact with respiratory tract secretions from an infected person during the infectious period or from an asymptomatic carrier.

Asymptomatic colonization of H. influenzae is common, especially with non-typeable and non-type b capsular type strains. In neonates, infection can be acquired intrapartum by aspiration of amniotic fluid or by contact with genital tract secretions containing the organism.

  • Incubation Period
    Unknown; probably short, 2–4 days.

Period of Communicability

The exact period of communicability of Hib is unknown. However, the risk of infection persists for as long as organisms are present whether or not there is nasal discharge. Hib disease is considered non-communicable within 24–48 hours after starting effective antibiotic therapy. The period of communicability for non-b strains is unknown.

Risk Factors/Susceptibility

Most of what is understood regarding susceptibility and resistance is in relation to Hib. Invasive Hib disease is less common after five years of age even in the absence of immunization. This age-dependent susceptibility is likely attributed to acquisition of Hib immunity through asymptomatic Hib infection, the likelihood of which increases with age. Risk factors for disease include host factors (e.g., chronic disease) and exposure factors (e.g., large household size/crowding, child care attendance, low socioeconomic status, and school-aged siblings) that increase the likelihood of exposure to Hib.

Diagnosis & Laboratory Testing

Clinical evidence of invasive disease with isolation of H. influenzae from:

  • a normally sterile site
  • the epiglottis in a person with epiglottitis

or clinical evidence of invasive disease with detection of DNA in a normally sterile site (using validated NAAT)

Treatment Case Management

Antimicrobial therapy should be initiated immediately for invasive Hib disease to eliminate Hib colonization. Cases who are less than two years of age or who are a member of a household with a susceptible contact should additionally receive rifampin chemoprophylaxis prior to hospital discharge if cefotaxime or ceftriaxone were not used for treatment.

Information about the illness and immunization should be provided. Families should be informed that children who develop invasive disease when younger than 24 months of age are at risk of developing a second episode of disease and should be immunized according to the age-appropriate schedule for unimmunized children as if no Hib vaccine doses were previously received. Please refer to the current Publicly Funded Immunization Schedules for Ontario.

Secondary cases caused by non-type b or non-typeable H. influenzae strains are rare and chemoprophylaxis is not recommended for contacts of invasive non-b H. influenzae disease. Close contacts of a Haemophilus influenzae type B case will be identified and followed by Public Health staff to determine eligibility for chemoprophylaxis. Chemoprophylaxis is recommended to eliminate nasopharyngeal carriage of Hib bacteria and prevent secondary transmission. To effectively prevent secondary spread, rifampin chemoprophylaxis is recommended for household and child care contacts in specific situations. If chemoprophylaxis is indicated, rifampin dosages should be administered as soon as possible.

Patient Information

Additional Resources

Ministry of Health and Long-Term Care. “Publicly Funded Immunization Schedule for Ontario”, 2016.

Public Health Agency of Canada. “Haemophilus influenzae disease.”

References

Ministry of Health and Long-Term Care, Infectious Diseases Protocol, May 2018.

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