Brucellosis is a neglected infection that has a widespread geographic distribution. Based on an evaluation from the World Health Organization (WHO), brucellosis cases have been reported in more than 170 countries with about 500,000 new cases being reported each year. However, the actual number of brucellosis patients is much higher, and it is believed to be approximately 10–25 times the number of reported cases (1). This big discrepancy between the reported rate and the actual incidence rate is largely due to misdiagnosis and underdiagnosis, especially in endemic areas. With the aim of improving the diagnostic capacity, the National Health Commission of China released its updated Guidelines for the Diagnosis of Human Brucellosis (WS 269–2019) on July 1, 2019. Compared with the old guidelines (WS 269–2007), there are three major changes in the new guidelines including new detection methods, revised classification of brucellosis stages, and biosafety requirements. In particular, the new guidelines mention lateral flow assays (LFA) as one of the new detection methods that are expected to provide fast and simple point-of-care testing at county-level clinics and CDC labs.
The classification of brucellosis by the WHO, US CDC, and China CDC differ as shown in Table 1. According to WS 269–2019 (the updated guidelines of China CDC), brucellosis cases are classified as suspected, probable (clinically diagnosed), confirmed (laboratory confirmed), and covert infection. Probable cases of brucellosis are diagnosed based on a combination of epidemiologic exposure, clinical manifestations, and positive results of presumptive laboratory tests including the Rose Bengal test (RBT), enzyme-linked immunosorbent assay (ELISA), LFA, and Gram staining of Brucella spp. Confirmed cases are probable cases with a positive result for one of the following tests: standard agglutination test (SAT), complement fixation test (CFT), Coombs test, or isolation of Brucella spp
. In contrast, the WHO only classifies cases as suspected, probable, and confirmed, and does not list LFA, Gram staining, or CFT as diagnostic tests. Similarly, US CDC only classifies cases as probable and confirmed, and while it does not include RBT, CFT, Gram staining, or LFA, it does include PCR and BMAT. Case classification China CDC WHO US CDC Suspected case Epidemiologic exposure+clinical manifestations Epidemiologic exposure+clinical manifestations None Probable case Suspected case+presumptive diagnosis (RBT, ELISA, LFA, Gram staining of Brucella spp.) Suspected case+presumptive diagnosis (RBT+SAT ≥160) Epidemiologic exposure+clinical manifestations+presumptive diagnosis (SAT≥160, BMAT, PCR) Confirmed case Probable case+confirmatory diagnosis (SAT≥100, Coombs
IgG, CFT, Culture)
Probable case+confirmatory diagnosis (ELISA IgG, Coombs IgG, Culture) Probable case+confirmatory diagnosis (a fourfold or higher increase in Brucella antibody titer between acute- and convalescent-phase serum specimens obtained ≥2 weeks apart; Culture) Covert infection Epidemiologic exposure+confirmatory diagnosis+asymptomatic manifestations None None
Table 1. Definition and classification of brucellosis by China CDC, WHO, and US CDC.
The definitive diagnosis of brucellosis requires isolation of the pathogen from blood or other tissue and body fluids; however, the inability to isolate the pathogen does not rule out the infection. In contrast to bacterial culture, serological testing is more sensitive and, therefore, preferred in routine clinical practice. The main serology methods currently used in China are serum agglutination tests. One such test is RBT, which is a practical screening test that has low diagnostic specificity but is used in combination with SAT, a commonly-used test that is used as a confirmatory test. However, there is a lack of consensus about the diagnostic endpoint titer: the WHO and US CDC have set the minimum antibody endpoint titer at 1:160, but the minimum antibody endpoint titer in China is 1:100. When the result of the SAT test is suspicious, the Coombs test is recommended for confirmation as it can improve the accuracy of diagnosis. However, because the Coombs test kit has not been licensed by the China Food and Drug Administration (CFDA), it is not used in clinical or medical institutions and is only used for research.
ELISA (IgG and/or IgM) is another serological test that is sensitive, fast, and convenient for the detection of brucellosis. It shows high sensitivity and specificity and should be used as a routine lab test when brucellosis is suspected in clinical practice. LFA, another serological test, does not require extensive laboratory infrastructure or technical expertise, and compared to the standard SAT and/or culture, the sensitivity and specificity are higher at 92%–95% and 97%, respectively, in endemic settings (2). Thus, it seems that there are several viable options with regard to serological testing for the diagnosis of brucellosis. Therefore, based on newly published studies and clinical practices, China CDC initiated a process to assess the performance of new tests with the support of the National Health Commission.