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Comparative evaluation of four serological methods and a quantitative real-time PCR assay in asymptomatic subjects with a previous history of brucellosis

Abstract number: P1810

Castaño Aroca M.J., Navarro E., Andicoberry M., Lorente S., Solera J.

Objectives:Brucella spp. antibodies, despite falling to low levels, can remain measurable after recovery from acute brucellosis. This makes it difficult to distinguish between cured patients, chronic brucellosis patients and those healthy individuals living in areas in which brucellosis is endemic. This is the basis for the controversy in the definition of the chronicity of the disease. The presence of Brucella spp. DNA in clinical samples in this setting remains unknown.

The aim of the present study was to evaluate both serological tests and a quantitative real time PCR (QPCR) assay for the presence of Brucella melitensis DNA in a cohort of asymptomatic subjects with a well-documented history of brucellosis.

Methods: Twenty asymptomatic subjects that had been diagnosed with brucellosis between three and 12 years prior to the study were included. Subjects were followed ranging between three to 34 months (mean 15 months). Between three and 6 blood and serum samples (172 samples in total) were screened by QPCR, classical serological tests (Rose Bengal, standard agglutination test (SAT) and Coombs test) and the commercial Brucellacapt® test. The methodology used for detecting B. melitensis DNA have been previously described by our group(a).

Results: All subjects had negative Rose Bengal test results. The SAT test showed antibody titres in three (15%) subjects (range, 1/20–1/80). The Coombs test showed antibody titres in four (20%) subjects (range, 1/160–1/640). The Brucellacapt® showed antibody titres in 10 (50%) subjects (range, 1/40–1/160). Seropositive samples by SAT or Coombs test were also positive by Brucellacapt®.

Brucella melitensis DNA was found in five (25%) subjects with a mean bacterial DNA load of 218 copies/ml in blood samples. All of them had seropositive samples by the Brucellacapt® (range, 1/40–1/160). However, only five (33.3%) out of the remaining 15 subjects with negative QPCR samples had seropositive samples by Brucellacapt® (range, 1/40–1/80) (p = 0.03; two tails Fisher test).

Conclusion: The individuals harbouring B. melitensis DNA in their blood are more likely to show a seropositive sample than the remaining participants. These findings suggest that the presence of bacterial DNA at low levels derived from latent bacteria are capable of producing a week immune response in the host.

References

(a) Castano MJ et al, J Clin Microbiol 2009 Jul 1; 47(7):2084–9.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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