Haemophilus influenzae (invasive disease) Figure 1 2004
*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2004
Haemophilus influenzae is a gram-negative coccobacillus having two forms, a nonencapsulated and an encapsulated form. The encapsulated form is typeable and has been classified as serotypes a through f. Humans are the natural host with up to
80 percent of healthy individuals colonized with the nontypeable form.
Prior to the licensure of H. influenzae type b vaccine, H. influenzae type b (Hib) disease was the leading cause of bacterial meningitis in children. Since the introduction of conjugate Hib vaccine in 1990, the incidence of Hib disease in children has decreased dramatically in both the U.S. and Indiana. Invasive disease caused by H. influenzae type b and other serotypes can affect many organ systems. The most common types of invasive disease are bacteremia/sepsis, meningitis, epiglottitis, pneumonia, arthritis, and cellulitis. All invasive H. influenzae disease, regardless of age or serotype, is reportable in Indiana. Figure 1 shows the total number of Haemophilus influenzae cases reported by year for 2000-2004.
Indiana had 62 reported cases of invasive H. influenzae (all serotypes) disease in 2004 (Table 1). Disease incidence was lowest during the summer months with the greatest incidence in spring (Figure 2). Age-specific rates were greatest for infants under the age of 1 year (8.13) and older adults aged 80+ years of age (7.65). Figure 3 shows H. influenzae incidence by age group. Females (1.07) were more likely than males (0.91) to become ill with H. influenzae.
The incidence rates were highest among the following counties reporting five or more cases: Elkhart (3.1), St. Joseph (2.3), and Marion (1.5). Figure 4 shows counties reporting five or more cases of H. influenzae in 2004.
Of the 62 reported cases in 2004, 45 (73%) were serotyped. Two cases were serotyped as type b, the only type preventable by vaccine. The type b cases occurred in adults and, thus, were not preventable by vaccine, as H. influenzae type b (Hib) vaccine is given only to persons under age 5. Table 2 presents a breakdown of cases by serotype.
|Percent of Reported Cases by Serotype|
|Source: Indiana State Department of Health|
Because Hib vaccines protect against type b and no other strains of H. influenzae, serotyping of all H. influenzae isolates from patients (especially from those under age 5) with invasive disease is necessary to monitor vaccination program effectiveness and national progress towards Hib elimination. Serotype information is also needed to measure the sensitivity of the surveillance system and to detect the emergence of invasive disease from nontype b H. influenzae strains.
You can learn more about H. influenzae by visiting the following website: