Haemophilus Influenzae
(Invasive Disease, All Serotypes)
Current Case Definition for Surveillance
"Invasive disease due to Haemophilus influenzae
may produce any of several clinical syndromes, including
meningitis, bacteremia, epiglottis, and pneumonia."
Only H. flu meningitis was reportable in Maryland through
1987. In 1988, invasive disease due to H. flu type b (Hib)
became reportable in Maryland for all health care providers.
All invasive H. flu disease (clinically compatible cases
with either detection of H. flu type b antigen in CSF
or isolation of any H. flu from a normally sterile site,
irrespective of serotype status) became nationally notifiable
from 1991.
Active Surveillance
Active surveillance for all invasive H. flu disease (with
isolation of H. flu from a normally sterile site in Maryland
residents) commenced in November 1991 with the Bacterial
Invasive Diseases Surveillance (BIDS) Project, a CDC-funded
joint project of The Johns Hopkins University, School
of Hygiene and Public Health and the EDCP. BIDS conducts
active surveillance for data on H. flu isolates from sterile
sites from all medical laboratories in the state and performs
annual laboratory audits. Prior to this, data on H. flu
isolates was sought by the EDCP on a regular basis from
only the DHMH laboratory.
Thus, although invasive disease due to H. flu of types
other than b, non-typable H. flu, and cases in which typing
was not done, are not reportable in Maryland in spite
of being nationally notifiable, these cases are detected
and reported through the BIDS Project. BIDS Project staff
believe that only a few cases with Hib antigen detected
in CSF but without H. flu isolated from a normally sterile
site (and thus not covered by BIDS) are being missed by
their surveillance system.
Immunization
H. flu is the most common cause of bacterial meningitis
in the United States, accounting for an estimated 12,000
cases annually, primarily among children under five years
of age. The case fatality rate is 5%, and neurologic sequelae
are observed in 25% to 35% of survivors. Virtually all
cases of H. flu meningitis among children are caused by
strains of type b (Hib), the only serotype for which immunization
is available.
A polysaccharide vaccine with no efficacy in children
under 18 months of age and uncertain efficacy in older
children was used in the United States from 1985 to 1988.
Two conjugate vaccines with greater efficacy in infants
and children were licensed in late 1990. In January 1991,
the CDC recommended the introduction of routine immunization
in infancy for Hib. Three or four doses are currently
recommended by age 15 months, depending on the vaccine.
Maryland law currently requires age-appropriate Hib immunization
for all children less than 48 months of age for entry
into child care centers and preschool programs. Data on
vaccine coverage in Maryland are not yet available.
Epidemiology, 1988 - 1993 (see graphs)
There was a decline in the incidence of reported invasive
H. flu disease in Maryland from 1988 to 1991, and then
a sharp increase in 1992. The recent increase may have
been associated with the start of active case detection
in November, 1991. By far the highest incidence of disease
during this period was in infants, though there has been
a sharp decline in the number of cases over this period
in both infants and one to four year old children. Although
the incidence was lowest in those over four years of age,
there was a sharp increase from earlier years in number
of reported cases in adults over 19 years of age in 1992
and 1993.
Serotype-specific data (from the BIDS Project) is available
for 70% of cases with first positive cultures in 1992
and 1993. Among the 105 cases of all ages with information
on serotype, 57% were type b (with similar percentages
type b in all four age groups). There was a sharp decline
from 1992 to 1993 in the number of reported cases with
serotype b in infants and in adults. There appeared to
be no geographical clustering of areas with a high incidence
of invasive H. flu disease of all serotypes during this
six year period.
The CDC reports that the incidence of H. flu disease
in the United States "decreased 95% between 1987
and 1993.Summary of Notifiable Diseases, United States,
1993. MMWR published October 21, 1994, for Vol. 42, No.
53, 1993. Data collected by active surveillance from selected
sites indicate that the decline is primarily in H. flu
type b (Hib) disease among children under five years of
age. This decline is associated with the use of the newly
licensed Hib conjugate vaccines."
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