Epidemiological surveillance of melioidosis in Singapore

During the period 1989 to 1996, a total of 372 cases of melioidosis, with 147 deaths, were reported, giving a mean annual incidence rate of 1.7 per 100,000 population and a case-fatality rate of 39.5%. Majority (89%) of the clinical cases were confirmed by culture of Burkholderia pseudomallei, while the others were presumptive cases based on a single blood specimen with an indirect haemaglutination (IHA) antibody titre of > or = 1:16. The highest incidence rate was reported in those aged 45 years and above (5.7 per 100,000 population), males (2.8 per 100,000 population), and Indian ethnic group (3.0 per 100,000 population). Cases were distributed throughout the island all year round. There was no correlation with rainfall. Most of the cases (77.4%) had other concurrent medical conditions, the most common being diabetes mellitus (57.5%). Factors significantly associated with a higher case-fatality rate were age (55 years and above), septicaemia, smoking history and heart or renal failure. The overall case-fatality rate has been declining from 60% in 1989 to 27% in 1996 due to a greater awareness among medical practitioners to diagnose and treat the disease early. The overall seroprevalence of IHA antibody (titre of > or = 1:16) among asymptomatic population groups was 0.2%. B. pseudomallei isolated from clinical specimens were sensitive to imipenem (100%), ceftazidime (99.1%), piperacillin (99.7%), ampicillin-clavulanate (98.5%), minocycline (97.4%), chloramphenicol (94.3%), doxycycline (94.3%) and tetracycline (93.9%). Of 395 samples of soil collected during epidemiological investigation of reported cases, 1.8% were positive for B. pseudomallei.