Longitudinal clearance of seasonal influenza A viral RNA measured by real-time polymerase chain reaction in patients identified at a hospital emergency department

Abstract

To study influenza virus shedding during acute infection, viral load was longitudinally measured by quantitative PCR in nasal flocked swabs from patients with seasonal H3N2 influenza at a Swedish emergency department, including both hospitalized patients and outpatients. Influenza A was detected in 65/184 patients. Sampling was repeated every 3–4 days in 45 patients, with the aim of continuing sampling until day 12 after disease onset. Home visits were offered. Antibodies were measured on paired sera in 95/184 patients. Fifty percent of the patients remained polymerase chain reaction (PCR)-positive 8 days after disease onset in a Kaplan–Meier survival curve. The longest observed duration of viral shedding was 12 days. The average viral load was initially low, peaked on days 2–3 of disease and then declined. Viral decline results remained similar when all 15 (25%) oseltamivir-treated patients were excluded. Significant antibody titre changes were seen in all the 35 PCR verified cases with available paired sera and in 8 of the 58 patients with negative PCR tests on acute phase nasal samples. In conclusion, quantitative PCR testing indicated the presence of influenza virus for up to 12 days, which could have implications for disease transmission and infection control.

Acknowledgements

The study was funded by grants from the Region of Skåne and grants from Lund University. The authors wish to express their thanks to all patients and staff, in particular to Carina Linder and Maria Rissler for excellent secretarial assistance and to nurses Lena Eriksson and Marie Faxheden who undertook home visits (sometimes travelling by bicycle) to obtain follow-up samples. We would also like to thank associate professor Peter Höglund, Competence Centre for Clinical Research, Lund, for statistical advice.

Declaration of interest: None of the authors declare any conflict of interest.