RESUMEN
The purpose of this study was to determine the rate of decline in the diagnostic yield of influenza PCR assay after oseltamivir administration, and to identify risk factors for prolonged shedding. This was a prospective observational study. We included adult inpatients with clinical signs of influenza during the influenza seasons 2015 and 2016, who had positive influenza PCR tests and who were treated with oseltamivir. Clinical follow-up and repeat PCR testing were performed on days 2, 4 and 6 after the first positive test. We defined prolonged shedders as patients who still required hospitalization and had a positive PCR assay on day 4. Risk factors for prolonged shedding were assessed in univariate and multivariate analyses. A total of 215 patients were included in our study. The median age was 64 years and 49.3% were men. The main influenza type was H1N1 (50.1%). Rates of PCR positivity among evaluable patients on days 2, 4 and 6 were 142/215 (66%), 50/78 (64.1%) and 20/30 (66.6%), respectively. Independent risk factors for prolonged shedding (50 patients) included hypoxemia [odds ratio (OR) 2.55, 95% confidence interval (1.3-5.1)] and lower diastolic blood pressure [OR 0.94, 95% CI (0.92-0.97)] on admission. Negative PCR tests taken more than 48 h after initiation of treatment had low diagnostic yield. More severe disease, manifested by hypoxemia and lower blood pressure, is associated with prolonged shedding on oseltamivir treatment.