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2005 Indiana Report of Infectious Diseases

Haemophilus influenzae (invasive disease)

Table 1. Haemophilus influenzae (invasive disease) Cases by Race and Sex, Indiana, 2005
  2005 2001-2005
Cases Rate* Cases
Total 71 1.13 295
Race
   White 51 0.92 241
   Black 10 1.80 31
   Other 0 0 2
   Not Reported 10 - 21
Sex
   Male 34 1.10 133
   Female 37 1.16 162
   Not Reported 0 - 0

*Rate per 100,000 population based on the U.S. Census Bureau’s   population data as of July 1, 2005

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 2001-2005.

Indiana had 71 reported cases of invasive H. influenzae (all serotypes) disease in 2005 (Table 1). Disease incidence was lowest during the summer and fall months with the greatest incidence in spring (Figure 2). Age-specific rates were greatest for older adults aged 80+ years of age (7.02) and for infants under the age of 1 year (6.97). Figure 3 shows H. influenzae incidence by age group. Females (1.16) were slightly more likely than males (1.10) to become ill with H. influenzae. The rate for blacks (1.80) was almost twice as high as that for whites (0.92).
Although 31 counties reported cases of H. influenzae, only Marion (16) and Elkhart (5) had 5 or more cases (Figure 4).

Of the 71 reported cases in 2005, 51 (72%) were serotyped. Table 2 presents a breakdown of cases by serotype.

Table 2. Percent of Cases by Serotype, Haemophilus influenzae (invasive disease), Indiana, 2005
Percent of Reported Cases by Serotype
 Type Number Percent
 a 0 0
 b 0 0
 c 0 0
 d 1 1.5
 e 1 1.5
 f 10 14.0
 Nontypeable 39 55.0
 Not Tested/Unknown 20 28.0
 Total 71  
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 Web site:
http://www.cdc.gov/ncidod/dbmd/diseaseinfo/haeminfluserob_t.htm 

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