we analyzed the epidemiologic data of all cases of melioidosis reported by registered medical practitioners and laboratories to the singapore ministry of health during 19982007 . clinical and laboratory criteria for notification were based on guidelines disseminated by the ministry ( 5 ) . upon notification , trained public health officers carried out epidemiologic investigations by using a standardized form . investigations included interviews with the patient or family members and a review of hospital records and laboratory results . data obtained included age , gender , date of onset of the illness , travel history , possible occupational or recreational exposure to contaminated soil or water , concurrent medical conditions , laboratory and microbiologic results , and clinical outcome . clinical specimens from patients with melioidosis were sent to clinical laboratories in the admitting hospitals for culture of b. pseudomallei ( 6 ) and , in some cases , for serology . was defined as a clinically compatible case in which b. pseudomallei was isolated from a clinical specimen . if the diagnosis was based on an indirect hemagglutination test that showed a titer > 16 ( 8) , the case was considered presumptive . both definitive and presumptive cases the estimated midyear population used for the calculation of the incidence rate was obtained from the singapore department of statistics . data on rainfall was obtained from the meteorological services division of the national environment agency . a total of 693 cases of melioidosis were reported during 19982007 ; of these , 83% were diagnosed by culture and 17% by serologic analysis . we observed a decreasing trend in the annual incidence rate , with the exception of an increase in 2004 ( figure 1 ) . the highest age - specific incidence rate of melioidosis was for adults > 45 years of age . an increase in the number of cases in march and april 2004 was preceded by heavy rainfall ( figure 2 ) , strong winds , and flash floods . a total of 23 cases of melioidosis were reported with onset of illness during the 5-week period between march 7 and april 10 ( epidemiologic weeks 1014 ) . the proportion of cases with the pneumonic form of melioidosis during this period was 82.6% , compared to 47.8% for the remainder of 2004 . only 4 of the 23 case - patients ( 17.3% ) reported occupations that had exposure to soil , e.g. , construction workers or gardeners . incidence ( per 100,000 population ) and case - fatality rate ( % ) of melioidosis cases , singapore , 19982007 . weekly melioidosis cases by onset date and rainfall totals , singapore , january 4 , 2004january 1 , 2005 a total of 112 deaths were reported during the 10-year period ; overall case - fatality rate was 16.2% ( range 8.8%27.1% ) . of the reported cases , 75.5% had co - existing diseases , with diabetes ( 47.9% ) , hypertension ( 26.4% ) , renal impairment ( 13.3% ) , and ischemic heart disease ( 12.0% ) being the most common . patients with co - illnesses had a significantly higher case - fatality rate ( 19.3% ) compared to those without ( 6.5% ) ( p<0.0005 ) . patients with bacteremic melioidosis had a significantly higher case - fatality rate ( 25.8% ) than those without bacteremia ( 5.5% ) ( p<0.0005 ) . clinical isolates of b. pseudomallei demonstrated antimicrobial sensitivity to imipenem ( 100.0% ) , ceftazidime ( 99.1% ) , doxycycline ( 99.0% ) , amoxicillin / clavulanate ( 94.2% ) , and chloramphenicol ( 96.1% ) . our study showed that male gender , old age , and diabetes mellitus were risk factors for melioidosis . the presence of bacteremia and co - illnesses were risk factors for death in patients with melioidosis , consistent with findings in other endemic countries . the overall case - fatality rate in this study was much lower compared to cases during 19891996 ( 39.5% ) ( 10 ) . this may be due to greater awareness among medical practitioners , earlier recognition of the disease , better intensive care , and an appropriate antimicrobial drug regimen . unlike patients in australia or thailand , most of the case - patients in our study could not recall any occupational or recreational exposure to wet soil . the only reported episodes of percutaneous inoculation in singapore were a few young adults with localized cutaneous infections and abscesses caused by occupational exposure to soil ( 4 ) . b. pseudomallei was isolated from only 1.8% of soil samples and from none of the water samples in singapore collected during epidemiologic investigations of reported cases ( 11 ) . tan et al . have suggested that in an urban setting excessive soil excavations could contribute to aerosolization of the bacterium ( 12 ) . rapid molecular typing of the bacteria during the outbreak in 2004 showed that the isolates were genetically heterogeneous , thus excluding the possibility of a common source ( 13 ) . moreover , the cases were distributed in different parts of the island without any particular geographic predilection . an epidemiologic investigation of cases in the first half of 2004 demonstrated a relationship between incidence of melioidosis and cumulative rainfall 7 days before onset of illness ( 14 ) . this finding is consistent with other studies that demonstrated an association between incidence of melioidosis and intensity of rainfall . researchers have posited that heavy rainfall causes movement of the bacteria to the surface with the rising water table ( 15 ) . severe climatic events may cause aerosolization of the bacteria and increase the risk for inhalation . infection following inhalation of b. pseudomallei may result in more fulminant disease and a higher case - fatality rate ( 15 ) . although the incidence and case - fatality rate of melioidosis in singapore has decreased , it has the potential to resurface with adverse climate events such as heavy rainfall and flash floods .
the incidence of melioidosis in singapore decreased during 19982007 , with the exception of the first quarter of 2004 . after heavy rainfalls , 
 an increase in pneumonic cases with a high case - fatality rate was detected . 
 we show that melioidosis has the potential to reemerge following adverse climate events .