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The high HIV-1 prevalence in drug users and their frequent sexual mixing with the non-drug-using population suggests that preventive interventions for reduction of high-risk drug taking and sexual activities are urgently needed in these populations. Interventions through public sexually transmitted infection (STI) clinics are unlikely to have much impact, as only 16% of IDUs with an STI attended a public STI clinic.

viruses than it did in A/H1N1 viruses. Two reassortants, one influenza A/H3N2 strain and one A/H1N1 strain, were found on the basis of the phylogenetic analysis of the three genes. While both genetic mutation and reassortment contributed to their evolution, the frequency of genetic changes and reassortment events differs between the two subtypes. As influenza viruses circulate throughout the year, we emphasize the importance of surveillance in tropical and subtropical zones, where the emergence of new strains may be detected earlier than it is in temperate zones.