Influenza A Outbreak in an Ambulatory Stem Cell Transplant Center

Background. In the era of cost-consciousness regarding healthcare, provision of medical services in an outpatient setting has become increasingly attractive. We report an influenza outbreak in an ambulatory stem cell transplant center in 2013 that highlights unique identification and infection control challenges in this setting. Methods. Nasopharyngeal swabs were performed on patients with suspected influenza-like illnesses (ILI), defined by subjective fever or measured temperature of >= 37.7 degrees C (>= 100 degrees F) with cough or sore throat during July 25, 2013 through August 7, 2013. In addition, testing was triggered by an elevated C-reactive protein (CRP). Specimens were analyzed by using eSensor Respiratory Viral Panel. Clinical and epidemiologic information was collected in real time, and frequencies were calculated on demographics, baseline clinical parameters, treatment methods, comorbidities, and symptoms of affected persons. Results. Thirty-one patients had influenza A (H3N2) infection during July 25, 2013 through August 7, 2013. Only 7 patients (23%) met the Centers for Disease Control and Prevention and Council of State and Territorial Epidemiologists ILI case definition. Twenty-five patients (81%) had received >= 1 transplant, with 13 (42%) having occurred within 1 year before the outbreak. Twenty-five patients (81%) had received B-cell active chemotherapy <60 days before influenza diagnosis, 6 (19%) were neutropenic, and 25 (81%) lymphopenic. Among clinical and laboratory markers analyzed, abnormal CRP was the most sensitive screening tool for influenza. Twelve (39%) patients were hospitalized (median stay, 10 days; range, 2-20). No deaths occurred. Conclusions. Immunocompromised hosts with influenza have atypical presentations. Existing surveillance case definitions might be insufficient to reliably identify influenza outbreaks in such patients.