Study of differential diagnosis of flu-like diseases with emphasis on brucellosis, in Narok District, Kenya
Flu-like diseases that present with non-specific symptoms pose big diagnostic problems to clinicians. Brucellosis, malaria, typhoid, streptococcal infections and rheumatism, which are in this category, were studied to gather characteristic data that could aid in their differential diagnosis. The study was conducted in Narok District, a typical pastoral region in Southern Kenya bordering Tanzania, where cultural, environmental and economic conditions allow these diseases to be prevalent. Specific study centres were the District hospital and three outlying dispensaries Mararianta, Siyapei and Olasiti. These centres were selected because they were better equiped and easily accesible. Patients sampled in these health units were also representative of the reference population. Brucellosis, a worldwide zoonosis that causes great economic losses, has not been diagnosed much in humans in Kenya and especially Narok District. However, recently created awareness in the region has caught the attention of some clinicians who are now testing for brucellosis although the vast majority of health centres do not. Brucellosis patients who are not tested are mostly treated for other diseases, mainly malaria. Malaria is a major differential of brucellosis and is present in Narok to a great extent (prevalence of 68%; Muriuki, 1994). In most health units without laboratory facilities and where clinicians make diagnosis by elimination method, febrile patients have been treated for malaria as a first priority. This procedure, although desirable under the circumstances, masks other flu-like diseases which are also febrile. In this study, flu-like patients were sampled and studied prospectively, subjecting them to a series of tests for brucellosis(Rose-bengal plate test, Serum agglutination test, complement fixation test), malaria(Blood smear test), typhoid(Widal test), streptococcal infections(Anti-Streptolysin o test) and rheumatic fever (Rheumatoid factor test). Results showed that brucellosis, typhoid and malaria are common in Narok, and their respective prevalences were 12%, 40% and 9%. Previously, both brucellosis and typhoid have been underdiagnosed (estimated prevalence from hospital records was 0.02 and 0.03 respectively). Clinicians did not think that streptococcal infections existed in the District, yet 48 (9.8%) patients were positive on antistreptolysin-O test and 28 (5.7%) were positive on rheumatoid factor test. Findings in this study show that accurate clinical diagnosis of these diseases is difficult. Flu-like symptoms such as headache, fever, joint pains, unspecific body pains, sweats, chills and abdominal discomfort showed a low positive predictive value but a high negative predictive value. They could not be relied on to increase the likelihood of a positive test since their Odds Ratio's were statistically insignificant. When the patients were subjected to laboratory tests, the post-test probability of disease rose significantly. It is therefore necessary to subject flu-like patients to the screening tests such as those used in this study. They are simple and increase the likelihood of a correct diagnosis. Patients who were diagnosed as having brucellosis also showed a lot of mixed infections, especially typhoid and streptococcal infections. This suggests that patients with a high index of suspicion as brucellosis cases should be countertested for malaria and typhoid. For effective control of brucellosis in Narok, more studies will be required to identify the species of brucella which are prevalent in the region. The quality of water for human consumption also needs to be assessed as typhoid was found to be a major problem.