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The immunofluorescent detection of specific antibodies to Chlamydia trachomatis, Chlamydophila pneumoniae, and C. psittaci may be complicated by crossreactive antibodies, non-specific antibody stimulation, or past exposure to more than one of these organisms. IgM titers of 1:10 or greater are indicative of recent infection; however, IgM antibody is very crossreactive, often demonstrating titers to multiple organisms. Any IgG titer may indicate past exposure to that particular organism. Infection by a particular organism typically yields IgG titers that are higher than antibody titers to non-infecting organisms. IgA titers may help to identify the infecting organism when crossreactive IgG is present. IgA is typically present at low titers during primary infection, but may be elevated in recurrent exposures or in chronic infection.