A reassessment of in the diagnosis of brucellosis in Iran: ELISA or PCR?

Abstract number: P1399

Hasibi M., Amirzargar A., Soudbakhsh A., Jafari S., Hajiabdolbaghi M., Asadollahi M., Abouzari M.

Objectives: Brucellosis is a worldwide infectious disease that poses an important public health problem especially in Iran. The development of a definite diagnostic test for brucellosis has been actively pursued. In the present study, the value of ELISA as an alternative method for the diagnosis of brucellosis has been investigated and compared with peripheral blood PCR assay.

Methods: A total of 37 consecutive patients with definite diagnosis of brucellosis (confirmed by blood culture and standard agglutination test) in Infectious Diseases Department of Imam Hospital, Medical Sciences/University of Tehran were prospectively evaluated. Moreover, blood samples from 78 controls (34 healthy controls and 44 non-brucellosis febrile patients) were included in the study. The peripheral blood PCR assay and ELISA IgG test were performed in patients and controls. In control group we calculated the mean of IgG levels plus 2 standard deviation (SD) as a cutoff value for ELISA IgG. The PCR target sequence of 223-bp present on a gene encoding a 31-kDa Brucella abortus antigen was selected for amplification.

Results: The blood culture was positive in 21 patients. The SATs were 1:160 and 1:320 in 35 (94.5%) and 28 (75.6%) patients, respectively. The positive results of PCR were observed in 15 (40.5%) patients and none of the controls. In patients and controls the mean levels of ELISA IgG were 171.33 ± 72.27 IU/ml and 19.78 ± 41.71 IU/ml, respectively. The cutoff point (mean plus 2 SD) was 103.2 IU/ml. The ELISA IgG had positive results in 33 (89.1%) patients and 4 (5.1%) controls. In 4 patients with negative results of ELISA IgG, serum level of IgM was measured by ELISA test. We found that the serum IgM level was more than 200 IU/ml in these 4 patients. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were reported 40.5%, 100%, 100%, 78% for PCR assay and 89.1%, 94.8%, 89.1%, 94.8% for ELISA test.

Conclusion: The results of the present study suggest that the ELISA test is the most sensitive method for the diagnosis of brucellosis and with the calculation of cutoff point it would be a reliable test. PCR assay is promising but standardisation of method is lacking and more investigations should be performed for better accuracy.