Evaluation of Serum Agglutination and Rose Bengal Tests against Immunofluorescence Antibody Assay in Diagnosis of Brucellosis in Narok and Kiambu County, Kenya
Nyagah, Susan, Nyawira
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Brucellosis in human is characterized by non specific signs and often misdiagnosed as malaria, typhoid, rheumatic fever and pyrexia of unknown origin. Definitive diagnosis of brucellosis requires isolation of Brucella '\PP.but chances of successful isolation decrease as the disease progresses. In Kenya, the current routine diagnostic test, Serum Agglutination Test (SAT) has a major drawback in that its not suitable for patient follow-up, since titers can remain high for a prolonged period. The alternative test, Rose Bengal Test (RBT) is not reproducible as it is very sensitive to vaccinal antibody limiting its use in vaccinated animals. Immunotlourescence antibody assay (IF A) has been described as the gold standard for diagnosis ofbrucellosis, To date there is no study in Kenya that has examined performance of the two ronrme tests STand RBT in the face of IFA The objective of this study was to evaluate SAT and RBT against IFA and to estimate the prevalence of brucellosis in Kiambu and Narok counties by the three diagnostic methods. Human blood and unpasteurised milk samples were collected between December 2009 and August2010 in Kiambu and Narok counties. A total of 250 human serum and 250 milk samples were collected from arok and Kiambu counties. Human serum sample was obtained from Kijabe referral hospital and other neighbouring health facilities. Antibodies to Brucella spp. were screened using SAT and RBTin the hospital and later transported to Kabete Veterinary Laboratory for IFA Milk samples were collected from milk vendors packed in cool boxes and transported to Kabete Veterinary Laboratory where screening was done using one step bovine Brucella antibody rapid test. All samples were subjected to IFA to determine the prevalence of brucellosis. The overall prevalence ofbnlcella antibodies by IFAas a gold standard was 3.2% and 70.4% and 14.4% and 54.4% in human samples and milk samples in Kiambu and Narok respectively. Prevalence by SAT was 10.4% and 77.6% and 8.3% and 80% by RBT in Kiambu and Narok respectively. Comparison of SAT and IFA gave PPV (63%), NPV (16.4%), sensitivity (75%) and specificity (74%). Comparison of RBT and IFA gave sensitivity (69.56%), specificity (72.78%), PPV(59.81 %) and NPV(19.58%). Comparison of One step bovine brucella rapid agglutination test and IFA gave sensitivity (16.5%), specificity (53.0%), PPV (19.76%) and NPV (52.43%). Prevalence was higher in females (68%) than males (32%) in Narok particulary 21-30 years. Both SAT and RBT should be scrapped as they lack sensitivity and specificity. IFA which is accurate, sensitive, specific, rapid should be recommended as the diagnostic test of choice. People handling animals and their products are at higher risk of infection.