Micro 443
Mark S. Chandler, Ph.D.
Haemophilus species
I.
Genus description
Small, pleomorphic, gram-negative rods
Non-motile, non-sporeforming
Facultative anaerobes
Genus name derived from Greek meaning “blood loving”
In vitro growth requires accessory growth factors found in blood
Some Haemophilus species require X factor (or Hemin)
Most Haemophilus species require V factor (nicotinamide adenine
dinucleotide or NAD)
Most Haemophilus species are normal residents of the upper respiratory tract of
humans or animals
The most common species of Haemophilus implicated in disease in humans are
H. influenzae and H. ducreyi
H. ducreyi causes chancroid, a sexually transmitted disease characterized by a
shallow genital ulceration
H. parainfluenzae is part of the human upper respiratory tract microbiota and only
occasionally causes of infection
II.
Haemophilus influenzae
H. influenzae was first described by Pfeiffer in 1892.
During a major outbreak of influenza, Pfeiffer found the organism in the sputum of
patients and proposed it to be the cause.
In 1933, Smith et al. showed that a virus caused influenza and H. influenzae was a
secondary infection.
Spread by inhalation of aerosolized respiratory droplets.
Major virulence factor of H. influenzae strains causing invasive disease is the
polysaccharide capsule.
Micro 443
Mark S. Chandler, Ph.D.
Six serogroups of encapsulated strains, a through f. Encapsulated strains known as
“typeable strains”

Unencapsulated strains referred to as “nontypeable strains”
H. influenzae can invade the bloodstream and cause infections at a distant site – invasive
disease. Possible reasons for this:

No antibodies to the capsule

Passive protection provided by transplacentally acquired maternal IgG
and breast-feeding during first 6 months

Peak attack rates at age 6-7 months; declines gradually; invasive
disease uncommon beyond age 5.

Preceding viral or Mycoplasma infection may be contributing factor
Invasive disease was due mostly to serotype b (pre-vaccine); now other serotypes cause
most invasive disease
The most common invasive diseases are

Meningitis- (~50% of cases of invasive disease) infection of
membranes covering the brain. Fever, decreased mental status, and
stiff neck. Mortality 2-5%, brain damage 15-30 %.

Epiglottitis- (17%) infection and swelling of epiglottis, the tissue in the
throat that covers the larynx during swallowing.

Septic arthritis- (8%)

Cellulitis (6%)

Pneumonia (15%)

Less common

Osteomyelitis (2%)

Pericarditis (2%) infection of the sac covering the heart
Unencapsulated (nontypeable) strains may also cause infection - usually at sites
contiguous with the upper respiratory tract –noninvasive disease

Otitis media – middle ear infection

Conjunctivitis – pink eye

Sinusitis

Acute bronchitis
Micro 443
Mark S. Chandler, Ph.D.
Laboratory Diagnosis:
Microscopic examination of Gram-stained smears of body fluids
If Haemophilus species suspected, must be cultured on chocolate agar as well as
appropriate media for other likely pathogens
Identification is done by determining X and V factor requirements
Vaccine
Consists of polyribosyl-ribitol phosphate conjugated to a protein carrier to make a more
effective antigen
Repeat doses elicit booster responses.
Protein carrier; diphtheria toxoid, tetanus toxoid, meningococcal group B outer
membrane protein
Incidence of type b disease has fallen 99% compared to the prevaccine era
Most cases now in unvaccinated or incompletely vaccinated children