HIV SeropositivityHIV SeroprevalenceHIV InfectionsSubstance Abuse, IntravenousSexual BehaviorRisk FactorsSeroepidemiologic StudiesAntibodies, ViralAntibodies, BacterialChlamydophila pneumoniaeAcquired Immunodeficiency SyndromeImmunoglobulin GChlamydophila InfectionsSerologic TestsEnzyme-Linked Immunosorbent AssayHIV SeronegativityPrevalenceHelicobacter pyloriHelicobacter InfectionsToxocariasisAntibodies, ProtozoanCytomegalovirus InfectionsAIDS SerodiagnosisHIV-1Cross-Sectional StudiesToxoplasmosisToxocaraHerpesvirus 2, HumanBlood DonorsHepatitis CHomosexualityCase-Control StudiesNeosporaRural PopulationPapillomavirus InfectionsBrazilCytomegalovirusSyphilisAIDS-Related Opportunistic InfectionsHerpes GenitalisToxoplasmaImmunoglobulin ACD4 Lymphocyte CountAnti-HIV AgentsAge Factors