This paper presents the results of research conducted on sera of 4830 patients hospitalized in 2009 in 4 clinical departments of the Institute of Rheumatology in Warsaw. The immunoenzymatic method (ELISA) was used and for confirmation of the presence of antibodies to Yersinia enterocolitica (only in children) and to Borrelia burgdorferi , the Western-blotting method was used. An increased level of antibodies to Yersinia spp. was found in 35.3% of sera and for other microbes, it was: Salmonella Enteritidis – in 13%, Chlamydia trachomatis – in 10.6% and B. burgdorferi – in 14.7% of sera (Table I). The presence of antibodies of particular classes (IgG, IgA and IgM) was analyzed considering their diagnostic usefulness in identification of infection. Special attention was paid to a very high prevalence (in the same serum) of antibodies directed to plural bacteria species (antibodies in the same class were detected in 56.8% and antibodies in different classes were detected in 20.7% of sera) (Table III, IV) . The presence of specific antibodies against Y. enterocolitica was confirmed in 60.8% of sera for IgA class and in 86.7% for IgG class. Analogically, the presence of specific antibodies against B. burgdorferi was confirmed in 82.2% for IgG class and in 45.9% for IgM class (Table II). Additionally, a detailed analysis of the prevalence of antibodies to specific antigens of Y. enterocolitica and B. burgdorferi was done (Fig. 1, 2). Serological diagnosis of undifferentiated arthritis of suspected bacterial origin: Yersinia spp., S. Enteritidis, Ch. trachomatis , B. burgdorferi is generally helpful, due to delayed onset of clinical symptoms. Unfortunately, there are some troubles with interpretation like:
• very frequent detection of antibodies in one class (especially IgG), which is not significant in the diagnosis of infective diseases,
• simultaneous prevalence of antibodies for 2 or 3 bacteria, what reflects the antibodies cross reactivity, additional infection or a previous contact with a pathogen,
• in many cases, confirmation with the use of specific methods is needed, what however considerably increases diagnostic costs.