Viral Shedding in University Students Infected by Influenza A(H1N1)pdm09, Nakhon Ratchasima Province, Thailand, June 2011

Abstract

Oseltamivir is often prescribed to treat influenza patients, yet its effect on viral shedding among Thai young adults infected with influenza A(H1N1)pdm09 virus remained unclear. During May to June 2011, an influenza A(H1N1)pdm09 outbreak was detected in University S, Nakhon Ratchasima Province, Thailand. A prospective observational study was conducted to define duration of viral shedding and immunologic response in infected students undergoing oseltamivir treatment, and identify factors associated with viral shedding. We enrolled all acute respiratory illness (ARI) patients attending the medical center at University S during 3-7 Jun 2011 with laboratory confirmation of influenza A(H1N1)pdm09 infection by real-time reverse transcription polymerase chain reaction (rRT-PCR). Additional throat swabs were collected and tested daily until rRT-PCR results became negative through two consecutive days. Series of serum samples for hemagglutination inhibition (HI) test were also collected from the individuals. Log-rank test was applied in analysis of association between patients’ characteristics and duration of viral shedding. Of 29 sick students enrolled, 45% were males. All were prescribed oseltamivir for five days and none of them were hospitalized. Median duration from onset of symptoms to the last day of viral shedding detected was five days (range 3-9 days). Over 80% of the patients had 4-fold rises of HI titer within 2-3 weeks after onset of symptoms. None of the patients’ characteristics were significantly associated with duration of viral shedding. However, persons with delayed antiviral treatment tended to have longer duration of viral shedding. Early oseltamivir treatment probably reduced risks of severe influenza in young adult patients. However, guidelines on infection control need to emphasize on strict hygiene and prevention measures in treated patients for nine days in order to minimize the risks of influenza transmission.