A retrospective observational study of the treatment of a nosocomial infection caused by oseltamivir-resistant influenza virus A with baloxavir marboxil.

Background: Nosocomial (hospital-acquired) influenza A virus infection is a very important clinical issue. The objective of this study is to describe the effect of baloxavir marboxil in controlling an outbreak of this infection.

Methods: A retrospective observational study was performed to assess the effectiveness of baloxavir marboxil in the treatment of nosocomial infections caused by oseltamivir-resistant influenza virus A.

Results: In September 2019, there was an outbreak of nosocomial influenza A(H1N1)pdm09 viral infection in one out of three facility wards for inpatients at the Okinawa Nanbu Regional Center for Children with Special Needs. Symptomatic staff members were kept off duty until they remained afebrile for 2 days. Prophylactic oseltamivir was administered to inpatients (n = 37) and to staff members (n = 16) who voluntarily requested the drug. However, both inpatients and staff members showed influenza A infection during prophylactic use of oseltamivir. The A(H1N1)pdm09 virus sample obtained from one patient was shown to be oseltamivir-resistant. After administration of baloxavir marboxil, the nosocomial outbreak gradually ceased. Moreover, the time (hours) to alleviation of fever in the oseltamivir group (n = 11) and baloxavir marboxil group (n = 13) was significantly different (p = 0.0034).

Conclusion: Our report provides evidence for the usefulness of baloxavir marboxil in treating influenza A patients who have received prophylactic doses of oseltamivir. This is the first report describing the successful use of baloxavir marboxil for of a nosocomial outbreak caused by oseltamivir-resistant influenza A virus.