Invasive Haemophilus influenzae disease in adults. A prospective, population-based surveillance. CDC Meningitis Surveillance Group.

OBJECTIVE

To define the incidence of and possible risk factors for invasive Haemophilus influenzae disease in adults.

DESIGN

Prospective, population-based surveillance of hospital and referral bacteriology laboratories.

SETTING

Metropolitan Atlanta, Georgia community.

PATIENTS

All patients with H. influenzae isolated from normally sterile sites (blood, cerebrospinal fluid, joint, pleura) from 1 December 1988 through 31 May 1990.

MEASUREMENTS

Isolates of H. influenzae were analyzed for serotype and biotype status, outer membrane proteins, lipooligosaccharide phenotypes, ribotyping patterns and beta-lactamase production.

RESULTS

A total of 194 cases of invasive H. influenzae occurred (annual incidence of 5.6 cases/100,000 population), of which 47 (24%) were in adults 18 years old or older (annual incidence 1.7 cases/100,000 adults). Adults with invasive H. influenzae ranged from 18 to 96 years; 79% were women. Bacteremic pneumonia accounted for 70% of the adult cases. Other sources for invasive H. influenzae in adults were obstetric infections, epiglottitis, and tracheobronchitis; one patient had meningitis. Underlying conditions were noted in 92% of the patients. Chronic lung disease was the most common risk factor, but pregnancy (annual incidence, 4.9/100,000 pregnant women), HIV infection (annual incidence, 41/100,000 known HIV-infected adults), and malignancy were also important. Overall mortality was 28% in adults, and over half of pregnancy-related infections resulted in fetal death. Fifty percent of the 40 isolates available for testing were serotype b; 47.5%, nontypable; and 2.5%, serotype f. Sixteen of the 45 isolates (36%) were ampicillin-resistant. Based on biotypes, outer membrane protein profiles, lipooligosaccharide phenotypes, and ribotyping patterns, the type b isolates showed less heterogeneity than the nontypable isolates but were distinguishable from one another.

CONCLUSIONS

Adult cases currently represent one quarter of all cases of invasive H. influenzae disease. Half of the reported adult cases were caused by type b H. influenzae, and the rate of ampicillin resistance in H. influenzae isolates from adults was higher than previously reported. Haemophilus influenzae is an important cause of bacteremia in compromised adults.