Haemophilus influenzae (invasive disease) 2003

Table 1. Haemophilus influenzae (invasive disease) Cases by Race and Sex, Indiana, 2003

  2003 1999-2003
Cases Rate* Cases
Total 59 1.00 227
Race
   White 48 0.90 196
   Black 8 1.50 19
   Other 0 0 1
   Not Reported 3 - 11
Sex
   Male 38 1.20 98
   Female 21 0.70 129
   Not Reported 0 - 0

*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2003

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 1999-2003.

Indiana had 59 reported cases of invasive H. influenzae (all serotypes) disease in 2003 (Table 1). Disease incidence was greatest during winter and summer months (Figure 2). Cases ranged in age from newborn to 101 years of age. Age-specific rates were greatest for infants under the age of 1 year (10.7) and older adults aged 80+ years of age (6.5). Figure 3 shows H. influenzae incidence by age group. Males (1.2) were almost twice as likely as females (0.7) to become ill with H. influenzae.

The only county reporting five or more cases in 2003 was Marion County, which had an incidence rate of 1.4 cases per 100,000 population.

Of the 59 reported cases in 2003, 43 (73%) were serotyped. Three cases were serotyped as type b, the only type preventable by vaccine. Two of 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. The other type b case occurred in a newborn infant who was not eligible for vaccine at the time of illness. Table 2 presents a breakdown of cases by serotype.

 

Table 2. Percent of Cases by Serotype, Haemophilus influenzae (invasive disease), Indiana, 2003

Percent of Reported Cases by Serotype

Type

Number

Percent

a

0

0

b

3

5.1

c

0

0

d

0

0

e

1

1.7

f

9

15.3

Nontypeable

30

50.8

Not Tested/Unknown

16

27.1

Total

59

 

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