Epidemiology
Reporting Obligations
Haemophilus influenzae disease, invasive is designated as a disease of public health significance and is reportable under the Ontario Health and Promotion Act. Report all suspect and confirmed cases immediately by phone to the health unit.
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 Schedules for Ontario", June 2022
Public Health Agency of Canada. “Haemophilus influenzae disease.”
References
Ministry of Health, Infectious Diseases Protocol - Ontario Public Health Standards, 2022.