Nosocomial Influenza Infection among Post-influenza-vaccinated Patients with Severe Pulmonary Diseases

Objectives: To report an outbreak of nosocomial influenza in thirteen out of twenty-two admitted patients suffering from severe lung emphysema. Methods: Acute-phase and convalescent serum samples of nine patients were collected. An antihaemagglutinin assay was performed to detect a rise in antibodies against influenza A virus. Further information about vaccination history of the patients and healthcare workers was included. Results: The majority of these twenty-two patients was vaccinated with a trivalent vaccine six months earlier. The immunological response showed that the influenza A (H3N2) strain which caused these infections is similar to the vaccine strain A/Sydney/5/97. Conclusions: The staff of our institute which was not systematically vaccinated may have been the source of infection. The time elapsed between the vaccination and the infection is the probable explanation of this event.