e304 13th International Congress on Infectious Diseases Abstracts, Poster Presentations Conclusion: These initial results indicate that aden- oviruses are a significant cause of respiratory disease among children under five. Specimen collection is on-going, and future results will further clarify the epidemiology of ade- novirus disease in Kenya. Subtyping of the isolates will be determined by PCR and reported. doi:10.1016/j.ijid.2008.05.813 46.033 Development of Novel Photo-inactivation Nanotechnology against Dengue Virus Y.L. Lee 1,* , D.K. Chatterjee 2 , Y. Zhang 2 , M.L. Ng 1 , J.J.H. Chu 1 1 Department of Microbiology, Yong Soo Lin School of Medicine, National University of Singapore, Block MD4, 5 Science Drive 2, Singapore, Singapore 2 Division of Bioengineering, Faculty of Engineering, National University of Singapore, Singapore, Singapore Background: Photodynamic therapy utilizes a photosen- sitizer, which upon excitation, emits energy that could be transduced by surrounding molecular oxygen to produce rad- ical oxygen species. Interaction between the singlet oxygen species and viruses may have a virucidal effect. In this study, the potential of using a novel photodynamic system to inac- tivate enveloped virus was investigated. Methods: The photosensitizer used was zinc- phthalocyanine (ZnPC), which was absorbed onto a novel two-photon nanotransducer (NaYF 4 ) that is activated by near infrared light (NIR). Dengue 2 virus was mixed with different concentrations of nanoparticles and exposed to a NIR light source at varying distances (5 cm and 10 cm) and durations (5 minutes and 10 minutes). The amount of surviving viruses was analyzed using plaque assay and compared with untreated virus samples. Further photo- inactivation study is being done on dengue 2 virus-infected HepG2 cells using nanoparticles that were conjugated with antibodies specific for the dengue virus envelope protein. The infected cells were incubated with the antibody- conjugated nanoparticles (4 to 110 g/mL) and subjected to NIR illumination (10 cm for 5 minutes). Results: The level of virus inactivation increased with higher nanoparticle concentrations and at shorter distance and longer illumination from the NIR source. At all con- ditions, virus inactivation was complete when 2.2 mg/mL nanoparticles were used and at 44 g/mL, virus titer was reduced by more than 50%. Conjugation with antibody may enhance the localization of the photo-inactivation site to targeted viruses or to virus-infected cells only, as shown by electron and laser scanning confocal microscopy. In addition, cell viability (MTT) assay showed that the photo- bleaching effect by NIR light on HepG2 cells was only minimal. Conclusion: Given its effectiveness in eradicating virus activity and its non-cytotoxic effect on cells, photodynamic therapy using NIR light could be a feasible novel technology with important implications in treating virus-infected blood or cellular samples. doi:10.1016/j.ijid.2008.05.814 46.034 Susceptibility to Oseltamivir and Amantadine of Human Influenza Viruses Circulating in Portugal V. Correia * , H. Rebelo-de-Andrade, L. Santos, M. Gíria Centro Nacional da Gripe, Instituto Nacional de Saúde (Research grant supported by Calouste Gulbenkian Founda- tion - Portugal), Lisboa, Portugal Background: Since 2002, increasing incidence of aman- tadine resistance has been detected worldwide. In a minor extent, emergence of oseltamivir-resistant strains has been identified during 2007/2008 winter season. This study aims to contribute to global surveillance on antiviral resistance and to risk assessment of drug use with continuous liber- ation of national data. Its main objective is to evaluate influenza virus susceptibility to oseltamivir and amantadine during 2004/2005—2007/2008, in Portugal. Methods: Susceptibility to oseltamivir was eval- uated by fluorescence assay in 233 strains from 2004/2005—2007/2008. NA and HA1 gene sequencing was performed in statistical outliers and in 30% of sus- ceptible strains, identified by fluorescence. Resistance to amantadine was evaluated by pyrosequencing in 128 strains from 2004/2005—2006/2007. Results: All 89 A(H3N2) and 94 B influenza strains tested shown to be oseltamivir-susceptible. Of the 50 A(H1N1) strains tested, 3 of the 14 from 2007/2008 were drug-resistant by exhibiting fluorescence-IC50 values approximately 400 times higher than the median value and mutation H274Y in NA sequence. Susceptibility to aman- tadine was detected in all 23 A(H1N1) strains tested. Resistance was found, by identification of mutation S31N in M2 sequence, in 24 of the 105 A(H3N2) strains tested: in the single strain from 2005/2006 and in 23 of the 35 strains from 2006/2007. Discussion: The origin of oseltamivir-resistant A(H1N1) strains in Portugal (2007/2008), and concurrently in other European countries, remains unclear. Their persistence through influenza seasons and their effect in viral evolution could become clearer with subsequent and continuous data analysis. Conversely, emergence of amantadine resistance in Portugal, identified in 2005/2006 and persistent through 2006/2007, probably derived from global spread of A(H3N2) virus bearing mutation S31N. These preliminary findings can presently contribute to monitor international dispersion of resistant viruses. Continuous and timely input of national data onto global surveillance constitutes the basis for risk assessment on antiviral drug use. doi:10.1016/j.ijid.2008.05.815 46.035 Management of Dengue in Patients on Antithrombotic Therapy H.C. Tan * , N. Chlebicka, B.H. Tan, H.N. Leong Singapore General Hospital, Singapore, Singapore Background: Recently, there has been a marked resur- gence of Dengue Fever (DF) in Singapore. More adults with chronic diseases including patients on antithrombotic ther-