Haemophilus influenzae (invasive disease) 2002

Table 1. Haemophilus influenzae (invasive disease) Cases by Race and Sex, Indiana, 2002

  2002 1998-2002
Cases Rate* Cases
Total 44 .71 219
Race
   White 39 .71 195
   Black 4 .76 15
   Other 0 0 1
   Not Reported 1 - 8
Sex
   Male 23 .76 86
   Female 21 .67 133
   Not Reported 0 - 0

*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2002

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 1998-2002.

Indiana had 44 reported cases of invasive H. influenzae (all serotypes) disease in 2002 (Table 1). Disease incidence was greatest during middle winter and early spring (Figure 2). Cases ranged in age from newborn to 90 years of age. Age-specific rates were greatest for the elderly aged 80+ years of age (7.12) and infants under the age of 1 year (4.7). Figure 3 shows H. influenzae incidence by age group. There was no significant difference in the incidence of invasive H. influenzae disease between genders in 2002.

The incidence rate was highest for Marion County (1.2), the only county reporting five or more cases in 2002 (Figure 4).

Of the 44 reported cases in 2002, 37 (84.1%) were serotyped. Three cases were serotyped as type b, the only type preventable by vaccine. One of the type b cases occurred in a 65-year-old individual and, thus, was not preventable by vaccine, as H. influenzae type b (Hib) vaccine is given only to persons under age 5. Two other Hib cases occurred in children under age 5 who were not vaccinated. Table 2 presents a breakdown of cases by serotype

Table 2. Percent of Cases by Serotype, Haemophilus influenzae (invasive disease), Indiana, 2002

Percent of Reported Cases by Serotype

Type

Number

Percent

a

0

0

b

3

6.8

c

1

2.3

d

0

0

e

2

4.6

f

6

13.6

Nontypeable

25

56.8

Not Tested/Unknown

7

15.9

Total

44

 

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.in.gov/isdh/25480.htm