INVASIVE HAEMOPHILUS-INFLUENZAE DISEASE IN ADULTS - A PROSPECTIVE, POPULATION-BASED SURVEILLANCE

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 13-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.