Quantification of Brucella melitensis DNA in patients with brucellosis

Abstract number: P1863

Navarro E., Castaño M.J., Alfaro-Martínez E., Segura J.C., Lorente S., Garijo L., Romero C., Beato J.L., Solera J.

In the present study we describe the evolution of bacterial load (B. melitensis DNA copies/ml of blood) at baseline, during therapy and post-therapy follow-up in patients with brucellosis. Patients were assigned to two different groups according to the evolution of the disease after treatment: non-relapse patients (group I) and relapse patients (group II).

To this aim, we applied the Real-Time Quantitative Polymerase Chain reaction technique (PCRQ) described by our team in a previous study [1]. Peripheral blood samples from 14 non-relapse (N = 103) and 8 relapse (N = 90) patients were analysed using PCRQ. Blood culture and serological tests were performed for each sample (rose bengal stain, serum agglutination test (SAT) and Coombs test).

The evolution of the bacterial load was similar in both groups during the acute episode. Basal load was 1619±2076 copies/ml (mean, s.d.) and 2778±3909 copies/ml for groups I and II, respectively. Bacterial load decreased during the first month of treatment in both groups, but the difference was statistically significant only for the non-relapse group (p = 0.03). Between day 29 and the end of treatment, bacterial load increased in mean value (930±2105 copies/ml and 677±1115 copies/ml for groups I and II, respectively) without reaching statistical significance (p = 0.205).

Follow-up of group I patients showed a decrease in bacterial load down to 120±274 copies/ml during the first three months. Thereafter, there was a mild increase in load until the ninth month of follow-up (220±475 copies/ml). At the end of the follow-up period, the bacterial load amounted to 22±34 copies/ml for 50% of non-relapse patients.

In relapse patients, bacterial load initially decreased to 83±78 copies/ml during the first two months of follow-up before relapse occurred. At the time of relapse, the bacterial load increased to 4626±7013 copies/ml, decreasing progressively with the re-instated treatment until the end of the follow-up period.

In patients with brucellosis, we were able to intermittently detect Brucella melitensis DNA after the treatment period, despite positive clinical response to therapy. We have been unable to determine the level of basal load that may be predictive of relapse. However, we found that only the non-relapse patients showed a significant decrease in the bacterial load during the first month of treatment.

References

1. Navarro et al, Clin Infect Dis 2006 May 1; 42(9):1266–73.