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\bibitem{Titti_etal1988} Titti, F., Rezza, G., Verani, P., Butto, S., Sernicola, L., Rapicetta, M., et al. (1988). HIV, HTLV-1, and HBV infections in a cohort of Italian intravenous drug abusers: analysis of risk factors. \textit{Journal of acquired immune deficiency syndromes}, \textit{1}, 405--411.

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