The Changing Epidemiology of Invasive Haemophilus influenzae Disease in Metropolitan Atlanta during the Hib Vaccine Era, 1989-2008 Open Access

Livorsi, Daniel Joseph (2011)

Permanent URL: https://etd.library.emory.edu/concern/etds/s1784m509?locale=en
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Abstract


Background: An effective Haemophilus influenzae type b (Hib) conjugate vaccine was
licensed in the U.S. for use in young children in 1987 and infants in 1990. We describe
changes in the epidemiology of invasive H. influenzae (HI) disease after Hib vaccine
introduction and evaluate predictors of mortality.

Methods: Population-based, active surveillance was conducted for HI in metropolitan
Atlanta, GA between 1/1/89 and 12/31/08.

Results: A total of 1207 cases of HI were identified during 1989-2008. The incidence of
HI decreased significantly between 1989 and 2008 (5.1 to 1.1 cases per 100K, χ2 trend
p<0.001). Rates of HI decreased significantly in all age groups except those ≥ 65 yrs.
The largest absolute decline of HI was in infants < 2 yrs (90.9 to 6.4 cases per 100K, χ2
trend p<0.001). Rates of Hib disease decreased in children (99% decrease, χ2 trend
p<0.001) and adults (96% decrease, χ2 trend p<0.001). Rates of capsule type f increased
in adults (205% increase, χ2 trend p=0.04).

The median age for HI cases was 10 months in children and 60 years in adults. Seventy-
one percent of adults and 23% of children had underlying conditions. The relative risk of
HI was higher in blacks than whites: 1.5 (95% CI 1.3-1.7). Children accounted for 73%
of cases in 1989-1990 but only 24% in 2000-2008. In 1989-1990, Hib caused 85% of HI
disease in children and 56% in adults. During 2000-2008, the most common isolates
were either nontypeable (66%) and type f (24%).

Overall in-hospital mortality rate was 12% (7% in children, 16% in adults). On
multivariate analysis of cases from 2000-2008, risk factors for in-hospital death included
age < 2 years, age ≥ 40 years, bacteremia without an identified focus, and nontypeable
disease.


Conclusion: Since introduction of the Hib conjugate vaccine, the incidence of HI disease
has significantly decreased in all age groups except ≥ 65 years. Hib disease has declined
in children and non-immunized adults. HI is now primarily a disease of adults with
chronic diseases due to nontypeable and type f strains. In-hospital death with invasive HI
infection was associated with the extremes of age and infection with nontypeable strains.

Table of Contents

Table of Contents:

Introduction.....1

Background.....3

Methods.....5

Results.....10

Discussion.....16

References.....20

Tables and figures.....22

Table 1. Characteristics of 1207 cases of invasive H. influenzae.....22

Table 2. Changes in the incidence of invasive H. influenzae disease by serotype for the overall population (n=1207).....23

Table 3. Changes in the incidence of type b, non-b, and type f isolates among children less than 18 years of age and adults.....24

Table 4. Changes in the incidence of invasive H. influenzae disease based on age groups.....25

Table 5a. Characteristics of invasive H. influenzae cases based on infecting serotype, 2000-2008 (n=525).....26

Table 5b. In-hospital mortality from invasive H. influenzae by clinical syndrome, 2000-2008 (n=522).....27

Table 5c. In-hospital mortality from invasive H. influenzae by age group, 2000-2008 (n=522).....27

Table 6. The occurrence of potential risk factors for in-hospital mortality among cases of invasive H. influenzae disease, 2000-2008.....28

Table 7. Odds ratios of potential risk factors for in-hospital mortality in cases of invasive H. influenzae disease, 2000-2008.....29

Table 8. Multivariate analysis for predictors of in-hospital mortality in 509 cases of invasive H. influenzae, 2000-2008 (all ages).....30

Table 9. Collinearity diagnostics for the logistic regression model of in-hospital death due to invasive H. influenzae disease.....31

Table 10. Wald Chi-Square test for interaction between predictor variables and clinical syndromes.....32

Table 11. Final restrained logistic regression model for predictors of in-hospital mortality in 509 cases of invasive H. influenzae, 2000-2008 (all ages, excluding type b).....33

Figure 1. Contribution of different age groups to the overall annual burden of invasive H. influenzae disease.....34

Figure 2. Incidence of invasive H. influenzae by serotype.....35

Figure 3. Proportion of invasive H. influenzae disease caused by each serotype among children and adults.....36

Figure 4. Causal diagram for potential contributors to in-hospital mortality from invasive H. influenzae.....37

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