HIV SeropositivityHIV SeroprevalenceHIV InfectionsSubstance Abuse, IntravenousSexual BehaviorRisk FactorsSeroepidemiologic StudiesAntibodies, ViralAntibodies, BacterialChlamydophila pneumoniaeImmunoglobulin GChlamydophila InfectionsSerologic TestsPrevalenceEnzyme-Linked Immunosorbent AssayHIV SeronegativityHelicobacter pyloriHelicobacter InfectionsToxocariasisCross-Sectional StudiesAcquired Immunodeficiency SyndromeAntibodies, ProtozoanCytomegalovirus InfectionsAIDS SerodiagnosisHIV-1ToxoplasmosisHerpesvirus 2, HumanToxocaraBlood DonorsHepatitis CAge FactorsRural PopulationNeosporaCohort StudiesCase-Control StudiesPapillomavirus InfectionsUnited StatesDisabled PersonsHerpes GenitalisSyphilisBrazilCytomegalovirusImmunoglobulin AOdds RatioToxoplasmaIncidenceHomosexuality, MaleCD4 Lymphocyte CountHepatitis A Virus, HumanHomosexualityImmunoglobulin MAntibodies, HelminthRisk-TakingAnti-HIV AgentsSexual Partners