HIV SeropositivityHIV SeroprevalenceHIV InfectionsSubstance Abuse, IntravenousSexual BehaviorRisk FactorsSeroepidemiologic StudiesAntiretroviral Therapy, Highly ActiveAnti-HIV AgentsCD4 Lymphocyte CountAntibodies, ViralHIV-1Antibodies, BacterialChlamydophila pneumoniaeImmunoglobulin GChlamydophila InfectionsViral LoadAcquired Immunodeficiency SyndromeHIV SeronegativitySerologic TestsPrevalenceEnzyme-Linked Immunosorbent AssayHelicobacter pyloriHelicobacter InfectionsAIDS-Related Opportunistic InfectionsToxocariasisCross-Sectional StudiesCytomegalovirus InfectionsCohort StudiesAntibodies, ProtozoanHepatitis CToxoplasmosisHerpesvirus 2, HumanToxocaraAIDS SerodiagnosisCase-Control StudiesBrazilBlood DonorsPapillomavirus InfectionsCytomegalovirusProspective StudiesNeosporaHomosexuality, MaleHomosexualityRural PopulationAge FactorsSyphilisHerpes GenitalisToxoplasmaUgandaIncidenceImmunoglobulin ARisk-TakingSexual PartnersSouth AfricaHepatitis BHIV AntigensOdds Ratio