Severity and recurrence of Haemophilus influenzae pneumonia in adults are frequent and associated with distinct...

Haemophilus influenzae is a frequent cause of community-acquired pneumonia (CAP) in adults, but determinants of severity and recurrence remain poorly described.

We performed a retrospective multicenter study in nine tertiary hospitals in Paris, France, from September 2022 to August 2023. Adults hospitalized for CAP H. influenzae were included. Severe pneumonia was defined by intensive care unit admission. Definite recurrence was defined as a new episode within 3 months, with repeat microbiological documentation of H. influenzae; probable recurrences within 1 month without microbiological confirmation were included in a sensitivity analysis.

Among 203 patients, the median age was 64.9 years, 61.6% were male, 56.2% had chronic pulmonary disease, and 44.0% were immunocompromised. Severe pneumonia occurred in 37 of 203 (18.2%) patients and was independently associated with chronic left-sided heart failure and chronic obstructive pulmonary disease. Definite recurrence occurred in 27 of 203 (13.3%) patients and was independently associated with humoral immunodeficiency, combined immunodeficiency, and close contact with children aged <5 years. In the sensitivity analysis, recurrence reached 52 of 203 (25.6%) when probable recurrences were included.

In hospitalized adults with H. influenzae CAP, severity was associated with cardiorespiratory comorbidities, whereas recurrence was associated with immune defects and exposure to young children.