BACKGROUND: Oseltamivir phosphate (OP; Tamiflu) is a prodrug of the 
anti-influenza neuraminidase inhibitor oseltamivir carboxylate (OC) and has been 
developed for the treatment and prevention of both A and B strains of influenza. 
The recent increase in OP resistance in influenza A virus (H1N1; commonly called 
"swine flu") has raised questions about the widespread use of Tamiflu in 
seasonal epidemics and the potential ecotoxicologic risk associated with its use 
in the event of a pandemic.
OBJECTIVES: The objectives of this study were to develop an analytical method 
for quantitative determination of OC in sewage treatment plant (STP) effluent 
and receiving river water, and to investigate the occurrence of OC in STP 
effluent and river water in Japan during a seasonal flu outbreak.
METHODS: We developed an analytical method based on solid-phase extraction 
followed by liquid chromatography-tandem mass spectrometry. Using this method, 
we analyzed samples from three sampling campaigns conducted during the 2008-2009 
flu season in Kyoto City, Japan.
RESULTS: The highest concentration of OC detected in STP discharge was 293.3 
ng/L from a conventional activated-sludge-based STP; however, we detected only 
37.9 ng/L from an advanced STP with ozonation as a tertiary treatment. In the 
receiving river water samples, we detected 6.6-190.2 ng/L OC, during the peak of 
the flu season.
CONCLUSION: OC is present in STP effluent and river water only during the flu 
season. Ozonation as tertiary treatment in STP will substantially reduce the OC 
load in STP effluent during an influenza epidemic or pandemic.