Jpn. J. Infect. Dis., 57, 224-225, 2004
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Laboratory and Epidemiology Communications
Seroprevalence of Anti-Flagellin Antibody against Burkholderia pseudomallei in Taiwan
Yao-Shen Chen1,2, Ssu-Ching Chen3, Tsu-Rong Wu4, Chih-Ming Kao5 and Ya-Lei Chen4*
1Section of Infectious Disease, Kaohsiung Veterans General Hospital,2Graduate Institute of Environmental Education and 3 Department of Biotechnology, National Kaohsiung Normal University, 4Department of Medical Technology, Fooyin Unversity, 5Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan
Communicated by Haruo Watanabe
(Accepted August 18, 2004)
*Corresponding author: Maling address: Department of Medical Technology, Fooyin University, 151 Chin-Hsuen Rd. Ta-Liao, Kaohsiung 83101, Taiwan, ROC. Tel: +886-7-7811151 ext 627, Fax: +886-7-7827162, E-mail: dan1001@ms31.hinet.net
Melioidosis in Taiwan is an emerging disease that was first described in 1984 (1). The etiologic agent is Burkholderia pseudomallei, an environmental saprophyte found mainly in endemic areas such as Southeast Asia and northern Australia (2). Since 1994, the number of reported cases of melioidosis in Taiwan have been steadily increasing (3). In at least 11 of these patients, infection appears to have been indigenous, rather than arising from travel to endemic areas (3-5). Since its clinical manifestations are quite protean, clinical diagnosis is often difficult, so the true incidence of melioidosis may actually be higher than is currently believed (6). Previously, a truncated flagellin antigen has been used with an indirect ELISA to detect the specific antibody against B. pseudomallei to distinguish B. pseudomallei septicemia from other bacterial infections in Taiwanese patients, having a sensitivity of 93.8% and a specificity of 96.3% (7). It has been reported that highly specific antibody titers against B. pseudomallei in populations correlate with the incidence of melioidosis and can indicate the prevalence of inapparent infection (8,9). Whether melioidosis in Taiwan will develop into an overt and widespread disease remains unclear at present. Accordingly, the seroprevalence of melioidosis was surveyed in various geographical regions in Taiwan. A related aim was to evaluate the prevalence of patients with bacterial pulmonary disease since pulmonary melioidosis is the most common form (>83%) of B. pseudomallei infection in Taiwan (3). In particular, a form of melioidosis also known as "Vietnam tuberculosis" can mimic tuberculosis both clinically and pathologically (10).
Serum samples from healthy donors were collected from Northern (Cathay General Hospital, Taipei; n = 200), Central (Hsing-Lin Hospital, Taichung; n = 180), and Southern (Kaohsiung-Veterans General Hospital [KVGH], Kaohsiung; n = 220), Taiwan. These donors have not been documented as having history of melioidosis. Patient serum samples (n = 152) were collected from KVGH. The melioidosis serum group (n = 17) was collected from confirmed patients, whom were identified based on bacterial cultures from blood. The patients with tuberculosis (n = 54) had diagnoses confirmed by bacterial cultures. The patient group with pneumonia (n = 81) had diagnoses based on chest X-ray findings, and diagnoses of tuberculosis or melioidosis had been excluded with bacterial cultures. All sera were frozen at -70C. Anti-B. pseudomallei flagellin antibodies were assayed using an indirect ELISA (7). When the average of the OD reading of the tested sample was greater than that of the negative controls plus two standard deviations, the tested sample was considered to be positive for the specific antibody. The highest dilution of the tested sample, which still gave a positive result, was defined as the endpoint titer and listed on the data sheet. The chi-square test was used to determine if a significant difference (P < 0.05) existed between tested groups.
With the indirect ELISA, a titer cut-off value of 1:256 was used in accordance with a previous study (7). Healthy donor serum seropositivities to B. pseudomallei flagellin were 4, 2.8, and 5% in the samples collected from Northern, Central, and Southern Taiwan, respectively (Table 1). The seroprevalence of melioidosis in the surveyed areas did not differ significantly (P > 0.5). At a dilution of 1:256, seropositivity was expected to distinguish melioidosis from tuberculosis and pneumonia (P < 0.001). A total of 152 sera with pulmonary disease were examined and seropositivity was found to be 94.1% (16/17) in melioidosis, 11.1% (6/54) in tuberculosis, and 2.5% (2/81) in pneumonia (Table 2). The pneumonia group had relatively low positive rates. Compared with the sera from healthy individuals by KVGH, the seropositivity of the tuberculosis group (6/54) was not significantly increased (11/220) (P > 0.1).
The seroprevalence of melioidosis usually reflects geography. For example, northeast Thailand is defined as a hyperendemic area where 80% of children have specific antibodies against B. pseudomallei, compared with 10-29% of healthy people in other parts of Thailand (11,12). The seroprevalence of melioidosis in Southern China's Hainan Island ranges from 8.8 to 66.7%, with the highest antibody titers found in farmers in the spreading areas of Xinglong (13). In contrast, the present study failed to identify significant differences in seropositivity attributable to geographical regions in Taiwan. Seropositive rates may be expected to be higher in tuberculosis patients since melioidosis can simulate pulmonary tuberculosis clinically, but neither the tuberculosis nor the pneumonia groups found to have a greater prevalence of anti-B. pseudomallei antibodies in those patients. Whether the slightly increased seropositive rate in tuberculosis patients is due to their earlier acquisition of an inapparent infection or their concurrent infection by both tuberculosis and melioidosis requires further study. Based on comparatively low and evenly distributed seropositive rates to melioidosis, it seems reasonable to conclude that Taiwan has not developed hyperprevalent areas although melioidosis cases have increased substantially. Nevertheless, seropositive rates of 2.8-5% with inapparent infection in the Taiwanese population highlights the need for physicians managing patients in Taiwan to be aware of the possibility of community-acquired pneumonia and sepsis arising from B. pseudomallei infection.
This work was supported in part by grants NSC91-2626-B-242-002 and NSC92-2314-B-242-011 from the National Science Council, R.O.C.
We would like to thank Chang Gang Memorial Hospital-Kaohsiung and Jiarren Hospital for supplying the melioidosis sera.
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