EVALUATION OF PCR, CULTURE AND SEROLOGY FOR THE DIAGNOSIS OF ACUTE HUMAN BRUCELLOSIS
Rabab A. Al-Attas, MD; Mohammad Al-Khalifa, MSc; Abdul Rahman Al-Qurashi, PhD; Mohammad Badawy, MD; Nafisa Al-Gualy, MBBS
Background: The diagnosis of brucellosis is frequently difficult to establish. This is not only because clinically, the disease can mimic any infectious and noninfectious disease, but also because the established diagnostic methods are not always successful. In this study, we have tried to evaluate PCR techniques in the diagnosis of brucellosis in comparison to conventional techniques. Patients and Methods: Fifty peripheral blood samples from the following groups were collected: patients with brucellosis (17); patients with febrile illnesses due to factors other than brucella etiology (19); symptomatic occupationally exposed persons (9); and healthy volunteers (5). The last three groups were considered controls. Among the 17 Brucella samples, only 14 were obtained before treatment was begun. The samples were tested by serology, using the standard tube agglutination method (STA), blood culture using Bactec machines, and PCR using primer pair to amplify a 223-bp region within a gene coding for a 31-kD Brucella antigen. Diagnosis of brucellosis was based on compatible clinical picture in addition to positive blood culture and/or positive serology. Results: Of the 17 blood samples from patients with brucellosis, eight were culture positive for Brucella species, and all showed high titer antibrucella antibodies. Only 14 of them were positive by PCR, and these were the samples submitted before initiation of therapy, representing 100% sensitivity. Among the 33 controls, blood culture was negative for Brucella in all of them, while one sample showed high-titer antibrucella antibodies. The latter was from the febrile illnesses group. PCR-based assay was able to detect four bands in the controls, all of which were from the occupationally exposed asymptomatic group. Conclusion: In view of the several advantages of PCR over the conventional methods for the diagnosis of brucellosis, such as speed, safety, high sensitivity and specificity, the technique might be considered for laboratory diagnosis of brucellosis. However, for the evaluation of asymptomatic highly exposed persons, PCR might be considered complementary to the traditional methods and followed up by serology and/or culture. Ann Saudi Med 2000;20(3-4):224-228.
Key Words: Brucellosis, PCR.
Brucellosis is a major cause of zoonosis, and an important public health problem in many parts of the world, especially in the Middle East. The disease is endemic in Saudi Arabia.1 Clinical presentation of the disease is nonspecific, and may be very atypical, therefore, laboratory confirmation by isolation or detection of specific antibrucella antibodies is essential for confirmation of the diagnosis. However, positive blood cultures occur in 10%- 70% of suspected infections,2 depending on the duration, localization of the infection and the type of Brucella species. Furthermore, culturing is time-consuming and
From the Immunology Department (Dr. Al Attas and Mr. Al-Khalifa), Regional Laboratory and Blood Bank, Dammam, Microbiology Department (Dr. Al Qurashi), King Faisal University Hospital, Al Khobar, and Infectious Diseases Department (Drs. Badawy and Al-Gualy), Dammam Central Hospital, Dammam, Saudi Arabia.
Address reprint requests and correspondence to Dr. Al Attas: Immunology Department, Regional Laboratory and Blood Bank, P.O. Box 831, Dammam 31421, Saudi Arabia. E-mail: firstname.lastname@example.org
serological tests are better than culture techniques, their specificities are low, especially in endemic areas or in people professionally exposed to Brucella. False-positive serological tests may also be caused by other illnesses such as salmonellosis, tularemia, cholera, lupus erythematosus and myeloma,2 while false-negative results may occur early on in the course of the disease3 or in case of focal infection.
of organisms, PCR-based assays have been applied recently to diagnose many infectious diseases. There are only a few reports on the use of PCR for the diagnosis of human brucellosis from peripheral blood samples.4,5 Moreover, the advantages of such techniques over the traditional conventional methods have not yet been clearly established. In this report, we compare the traditional diagnostic methods with PCR-based assay for the diagnosis of human brucellosis. To the best of our knowledge, this is
the first report of this kind in an endemic Arab area.
Accepted for publication 28 April 2000. Received 22 September 1999.
presents a major laboratory hazard, as Brucella spp. are class III pathogens. Although the sensitivities of the
Annals of Saudi Medicine, Vol 20, Nos 3-4, 2000