To describe the epidemiologic features of an outbreak of an acute respiratory tract infection (ARI) caused by β-lactamase-negative ampicillin-resistant (BLNAR) nontypeable Haemophilus influenzae (NTHi) in an acute-care ward.

Cross-sectional case-control study.

An acute-care ward (ward A) in a general hospital of Kochi in western Japan.

Patients who shared a room with an index patient and all staff in ward A were screened and followed from July 1 to August 31, 2015. Sputum or throat swab samples were collected from participants and tested by culture and polymerase chain reaction (PCR). The association between detected pathogens and ARI development among all participants was examined. A case-control study was conducted to identify risk factors for disease.

In total, 78 participants, including the index patient, were enrolled. Of all participants, 27 (34.6%) developed mild respiratory symptoms during a 3-week period: 24 were diagnosed as upper respiratory tract infections, and 3 were diagnosed as lower respiratory tract infections. The presence of BLNAR NTHi was confirmed in 13 participants, and multilocus sequence typing demonstrated that these isolates belonged to sequence type 159. All isolates showed identical pulsed-field gel electrophoresis patterns. The presence of BLNAR NTHi was strongly associated with ARI development, whereas viruses were not associated with the disease. Multivariate analyses demonstrated that a history of contact with the index patient was independently associated with ARI caused by BLNAR NTHi.

BLNAR NTHi has the potential to cause upper respiratory tract infections among adults and to spread rapidly in hospital settings.

Infect Control Hosp Epidemiol 2018;39:652–659