Clinical Characteristics and Adverse Clinical Outcomes of Invasive Haemophilus influenzae Serotype a Cases—United States, 2011–2015

Background Incidence of invasive disease due to Haemophilus influenzae serotype a (Hia) increased an average of 13% annually from 2002 through 2015. We describe clinical characteristics and adverse clinical outcomes of US invasive Hia cases detected through multistate surveillance during 2011–2015. Methods Medical record data were abstracted for cases reported in 8 jurisdictions conducting active population- and laboratory-based surveillance for invasive Hia disease across the United States. Isolates from sterile sites were serotyped using real-time polymerase chain reaction. Adverse clinical outcomes were defined as any possible complication of meningitis, bacteremic pneumonia, or bacteremia (including hearing loss and developmental delay, but excluding death) and were assessed at hospital discharge and one-year post-disease onset. Results During 2011–2015, 190 Hia cases were reported to the 8 participating sites; 169 (88.9%) had data abstracted. Many patients were aged <5 years (42.6%). Meningitis was the most common clinical presentation among those aged <1 year (71.4%); bacteremic pneumonia was the most common presentation among persons aged ≥50 years (78.7%). Overall, 95.9% of patients were hospitalized. Among those hospitalized, 47.5% were admitted to an intensive care unit and 6.2% died during hospitalization. At hospital discharge and one-year post-disease onset, adverse outcomes were identified in 17.7% and 17.8% of patients overall and in 43.9% and 48.5% of patients with meningitis (primarily children). Conclusions Hia infection can cause severe disease that requires hospitalization and may also cause short- and long-term adverse clinical outcomes, especially among children. Novel vaccines could prevent morbidity and mortality.