Risk Factors for Melioidosis and Bacteremic Melioidosis

Transcription

1 408 and Bacteremic Melioidosis Yupin Suputtamongkol, Wipada Chaowagul, Ploenchan Chetchotisakd, Nimit Lertpatanasuwun, Sunanta Intaranongpai, Theera Ruchutrakool, Duangkao Budhsarawong, Piroon Mootsikapun, Vanaporn Wuthiekanun, Nitaya Teerawatasook, and Aroonlug Lulitanond From the Department of Medicine, Faculty of Medicine, Siriraj Hospital, and the Wellcome Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok; Department of Medicine, Sappasitprasong Hospital, Ubon Ratchatani; Department of Medicine, Faculty of Medicine, and Department of Clinical Microbiology, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen; Department of Medicine, Srisaket Hospital, Srisaket; and Department of Medicine, Surin Hospital, Surin, Thailand A case-control study was conducted in four hospitals in northeastern Thailand to identify risk factors for melioidosis and bacteremic melioidosis. Cases were patients with culture-proven melioidosis, and there were two types of controls (those with infections, i.e., with community-acquired septicemia caused by other bacteria, and those without infection, i.e., randomly selected patients admitted with noninfectious diseases to the same hospitals). Demographic data, clinical presentations, and suspected risk factors were analyzed. Diabetes mellitus, preexisting renal diseases, thalassemia, and occupational exposure, classified by the soil and water risk assessment, were confirmed to be significant risk factors for melioidosis and bacteremic melioidosis. Only diabetes mellitus was a significant factor associated with bacteremic melioidosis, as compared with nonbacteremia. A significant interaction was found between diabetes mellitus and occupational exposure. Thus, diabetic rice farmers would be the most appropriate population group for targeted control measures such as vaccination in the future. Melioidosis is an infectious disease caused by a saprophytic bacterium, Burkholderia pseudomallei. The organism is widely distributed in the soil and water in the tropics, especially in northeastern Thailand [1]. In Ubon Ratchatani, in northeast Thailand, B. pseudomallei is one of the most common causative organisms of community-acquired septicemia [2]. Clinical presentations of melioidosis are protean, ranging from localized, benign infection to fulminant septicemia. Most patients who are admitted to the hospital have severe disease, and the case-fatality rate remains high despite recent significant advances in the antibiotic treatment regimens [3 5]. Patients who recover from acute melioidosis require an additional weeks of oral maintenance treatment [6]. Relapse of infection occurs in 10% of patients completing a full course of antibiotic treatment and is more common if patients do not complete the course of oral therapy. Clinical presentations of relapse are as severe as the initial infection, and the mortality associated with relapse is 30% [7]. Received 22 September 1998; revised 20 January Informed consent was obtained from all patients or their guardians before their enrollment in the study, and guidelines of the Thai Public Health Ministry were followed in the conduct of this study. This study was approved by the Ethical Review Subcommittee of the Research Committee of the Ministry of Public Health, Thailand. Financial support: This study was supported by The Thailand Research Fund. V. Wuthiekanun is supported by the Wellcome Trust of Great Britain. Reprints or correspondence: Yupin Suputtamongkol, Department of Medicine, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand (siysp@mahidol.ac.th). Clinical Infectious Diseases 1999;29: by the Infectious Diseases Society of America. All rights reserved /99/ $03.00 Current information on the epidemiology of melioidosis is very scanty, and it is derived mostly from case series and retrospective studies [8, 9]. A prospective study of risk factors for melioidosis, especially bacteremic or fatal melioidosis, is important so that preventive measures can be targeted directly to the population at highest risk. Materials and Methods This was a case-control study conducted in four hospitals in Thailand between January and December 1997: Srinagarind Hospital, Khon Kaen Province; Sappasitprasong Hospital, Ubon Ratchatani Province; Srisaket Hospital, Srisaket Province; and Surin Hospital, Surin Province. These hospitals are in the northeastern part of the country, where melioidosis is highly endemic. In these hospitals patients with suspected septicemia usually had three blood culture specimens taken by separate venipunctures at 15-minute intervals after disinfection of skin with iodine and alcohol. Five milliliters of blood was injected through a clean rubber stopper into a sealed bottle prepared by the hospital laboratory that contained 50 ml of brain-heart infusion broth. The bottle was then incubated aerobically. All patients with suspected melioidosis were admitted to one of the hospitals. In addition to the three blood culture specimens, clinical specimens from suspected sites of infection such as sputum or pus were taken. B. pseudomallei was identified as described previously [2], and all isolates were confirmed with use of the API 20NE biochemical identification system (Analytab Products, Basingstoke, UK).

2 CID 1999;29 (August) 409 Most patients with suspected community-acquired septicemia in these hospitals were treated initially with either a combination of penicillin G sodium or cloxacillin and gentamicin, if they were previously healthy, or a third-generation cephalosporin and/or gentamicin if they had an underlying disease such as diabetes mellitus. Patients with suspected severe or bacteremic melioidosis were treated empirically with either ceftazidime alone or ceftazidime plus co-trimoxazole. The antibiotic regimen was modified hours after admission, according to the microbiological diagnosis and clinical response to the initial drugs. Patients with culture-proven melioidosis were treated with parenteral antibiotics for at least 14 days or until they were clinically improved and afebrile for at least 48 hours. They were then switched to oral treatment with either a combination of oral co-trimoxazole and doxycycline or high-dose amoxicillin plus clavulanic acid for a total course of weeks. Selection of Cases Cases were adult patients ( 14 years old) with cultureproven melioidosis who were admitted to these hospitals during the study period. They were classified as having bacteremic or nonbacteremic melioidosis, depending on whether their blood cultures were positive or negative, respectively, for B. pseudomallei. The mortality associated with bacteremic melioidosis was very high when compared with that for nonbacteremic melioidosis [2 5, 10]. Thus, severe melioidosis was simply defined as bacteremic melioidosis in this study. Selection of Controls There were two controls for each melioidosis case, selected from among patients who were admitted to the same hospital at the same time (within 14 days) as cases. The first control group (infectious controls) comprised patients admitted with community-acquired septicemia caused by bacteria other than B. pseudomallei [2]. In brief, these patients were admitted because of suspected septicemia and had positive blood cultures within 48 hours of admission; in addition, a significant pathogen (not a possible contaminant such as Staphylococcus epidermidis) was isolated from them. The second control group (noninfectious controls) was created from the list of patients who were admitted to the same ward on the day that the melioidosis case was identified. The first patient from this list who was admitted with a noninfectious disease such as congestive heart failure or stroke could serve as a control. If a patient could not be enrolled in the study as a control, the next patient on the same list who met the study criteria was chosen. The exclusion criteria were age of 14 years old, positivity for antibodies to HIV, or a positive blood culture that was considered either not significant or possibly significant (i.e., it likely contained a contaminant) or was performed with a specimen drawn 48 hours after admission and thus was considered likely to have yielded a hospital-acquired organism. Data Collection Demographic data, estimated income per year, and suspected risk factors for melioidosis, such as occupation, history of regular self-treatment with any drug before hospital admission (such as herbal medicine, which might contain a steroid), and concomitant diseases were recorded prospectively. Occupation was classified into three classes according to the chance and extent of exposure to B. pseudomallei in the soil and water during the work. Rice farmers and cattle or pig farmers and their families were classified as having the occupation with the highest risk of B. pseudomallei contact from soil and water exposure. Current or retired government officers, clerks, businessmen, merchants, and their families were classified as the group with the lowest risk, provided they did not also work in rice fields. Patients with other occupations were classified as having an intermediate risk. Income levels were classified as low, intermediate, and high on the basis of average income per year (in United States dollars, $1,200, $2,400, and $2,400, respectively). Alcohol consumption was classified into three groups: none; modest, i.e., 3 drinks per day (115 ml of wine, 340 ml of beer, or 43 ml of 80-proof beverage represented 1 drink); and heavy, i.e., 3 drinks per day [11]. After a patient s enrollment in the study, serum samples were taken and urine samples were collected. A routine full blood cell count and serum biochemistry were performed. Plasma glucose and glycosylated hemoglobin (HbA 1 C) were measured in addition. Newly diagnosed diabetes mellitus cases were defined as patients who did not have a history of glucose intolerance and required neither oral hypoglycemic drugs nor insulin before admission and had an HbA 1 C level of 6% and/or a random plasma glucose value of 11.1 mmol/l. Plain abdominal radiography and/or abdominal ultrasonography were done to detect renal calculi. Preexisting renal disease was defined by the presence of renal or ureteric calculi and/or an abnormal creatinine level that was not considered to suggest acute renal failure resulting from this episode of infection. Diagnoses of thalassemia trait (or hemoglobin E trait) and thalassemia were confirmed by hemoglobin electrophoresis studies. The clinical courses and outcomes for all patients were also recorded. Statistical Analysis Demographic data, occupations categorized by the soil and water risk assessment, underlying diseases, history of drug use before admission, etc., were compared between patients with culture-proven melioidosis and both control groups. For continuous variables the Student s t test or the Mann-Whitney U

3 410 Suputtamongkol et al. CID 1999;29 (August) test was used, and for categorical variables either the 2 test with Yates correction or Fisher s exact test was used. Stepwise logistic regression analysis (with SPSS 7.5 for Windows; SPSS, Chicago) was used to identify independent risk factors for melioidosis and severe or bacteremic melioidosis. The logistic regression models were constructed with use of two groups of controls, one comprising patients with community-acquired septicemia due to bacteria other than B. pseudomallei (infectious controls) and another comprising the combined group of infectious and noninfectious controls. Results Melioidosis Group Overall, 204 patients with culture-proven melioidosis were enrolled in the study. B. pseudomallei was isolated from the blood of 102 of the patients (i.e., they had bacteremic melioidosis); 37 strains of this pathogen were isolated from urine, 51 from sputum, 104 from pus, and 54 from throat swab specimens. The overall mortality was 26% (36.3% and 16.5% in the bacteremia and nonbacteremia groups, respectively; P.001). Infectious Control Group Overall, 204 patients with positive blood cultures were identified. Fourteen of them either were dead or had been discharged from the hospital when blood culture results were available from the microbiology laboratory; therefore, we could not obtain information or plasma or serum specimens from them for the study. Nine patients were excluded from the analysis because they were considered subsequently to have hospital-acquired septicemia. Thus, 181 patients were eligible for the final analysis (50 patients [27.6%] with Escherichia coli septicemia; 28 [15.5%] with klebsiella septicemia; 13 [7.2%] with salmonella septicemia; 32 [17.7%] with other gramnegative septicemia; 24 [13.2%] with staphylococcal septicemia; 10 [5.5%] with Streptococcus pneumoniae septicemia; and 24 [13.3%] with other gram-positive septicemia). The overall mortality in this group was 26%. Noninfectious Control Group There were 204 patients in this group. Nine patients were excluded from the analysis because they developed fever (five) or were found to be HIV-positive during their hospitalization (four). Thus, 195 patients were eligible as noninfectious controls in the final analysis. A comparison of the three study groups with regard to factors such as demographic characteristics, socioeconomic status (assessed by yearly income), and concomitant diseases is shown in table 1. The baseline packed-cell volume, total WBC count, and values for total bilirubin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, urea, and creatinine were similar between the cases and infectious controls. These laboratory parameters were mostly within normal limits in the noninfectious control group (data not shown). Diabetes Mellitus Two-thirds of diabetic patients (129 of 210) in this study had a clear history of glucose intolerance requiring treatment with either insulin or oral hypoglycemic drugs (known diabetics). The proportion of patients with newly diagnosed diabetes mellitus to those with known diabetes mellitus was not significantly different between the three groups (43:80 in the melioidosis group, 20:29 in the other-septicemia control group, and 18:20 in the noninfectious control group). Mean ( SD) random plasma glucose and HbA 1 C levels were significantly higher in patients with melioidosis (12.1 [ 7.8] mmol/l and 8.3% [ 4.1%]) than in both control groups (8.6 [ 7.1] mmol/l and 6.1% [ 2.8%] in the other-septicemia group and 7.0 [ 4.7] mmol/l and 5.5% [ 2.0%] in the noninfectious group) (P.001). Among patients with known diabetes mellitus, the proportion in whom there was evidence of poor glycemic control before admission (i.e., their HbA 1 C levels were 7.5%) was similar in the group with melioidosis (65%) and the group with septicemia caused by other bacteria (62%). However, only 25% of patients with known diabetes mellitus in the noninfectious control group were considered to have poor glycemic control (P.001 vs. melioidosis or other-septicemia patients). The primary objective of this study was to determine risk factors for the first episode of melioidosis. Thus, 12 patients were excluded from the logistic regression analysis of the risk factors for melioidosis because they were admitted during a second episode or relapse of melioidosis. Overall, 163 (84.9%) of patients with melioidosis were rice farmers. Two-thirds of them (119/192) had an underlying disease, which predisposed them to melioidosis. Diabetes mellitus (115 patients; 60.9%) was confirmed to be the most common underlying condition associated with melioidosis in this study; the other common underlying conditions were preexisting renal disease (40 patients; 20.8%), thalassemia (14 patients; 7.3%), history of previous trauma or surgery (13 patients; 6.9%), pulmonary tuberculosis (12 patients; 6.3%), and hematologic malignancy or solid tumor (8 patients; 4.2%). Results of the logistic regression analysis revealed that diabetes mellitus, occupational exposure, preexisting renal diseases, and thalassemia were significant independent risk factors for melioidosis, as shown in table 2. Patients with hematologic malignancy or solid tumor such as cholangiocarcinoma or lymphoma were significantly less likely to develop melioidosis

4 CID 1999;29 (August) 411 Table 1. A comparison of the study groups with regard to demographic data and the distribution of important risk factors. No. (%) of patients with characteristic Characteristic Melioidosis Other sepsis Noninfectious P value Sex: male 126 (61.8) 99 (54.7) 115 (59.0).37 Age in years: mean ( SD) 52 ( 14) 50 ( 17) 51 ( 17).43 Occupation.007 High exposure 174 (85.3) 132 (72.9) 141 (72.3) Moderate 12 (5.9) 12 (6.6) 14 (7.2) Low 18 (8.8) 37 (14.9) 40 (20.5) Income.03 Low 172 (84.4) 138 (76.2) 143 (73.3) Intermediate 16 (7.8) 20 (11.0) 33 (16.9) High 16 (7.8) 23 (12.8) 19 (9.8) Smoker 92 (45.0) 66 (36.5) 73 (37.4).39 Alcohol Consumption.16 Modest 69 (33.8) 45 (24.9) 47 (24.1) Heavy 25 (12.3) 25 (13.8) 22 (11.3) Use of herbal medicine 20 (9.8) 24 (13.3) 9 (4.6).01 Underlying condition(s) None 73 (35.8) 66 (36.5) 87 (44.6) Diabetes mellitus 123 (60.3) 49 (27.1) 38 (19.5).001 New Renal disease 41 (20.1) 21 (11.6) 22 (11.3).01 Malignancy 8 (3.9) 25 (13.8) 19 (9.7).003 Chemotherapy or steroid therapy 6 (2.9) 20 (11.1) 15 (7.7).01 History of tuberculosis 12 (5.9) 6 (3.3) 2 (1.0).02 History of surgery 16 (7.8) 22 (12.2) 12 (6.2).10 Thalassemia or hemoglobin E trait 88 (44.2) 95 (55.2) 85 (45.4).35 Thalassemic disease 16 (8.0) 2 (1.2) 3 (1.7).001 Other 7 (3.4) 33 (18.3) 49 (15.1).001 than were patients without such underlying disease (OR, 0.4; 95% CI, ). Results were similar when data were analyzed for the infectious control group alone or in combination with the noninfectious control group (table 2). A significant interaction between diabetes mellitus and occupation was found in this study. This interaction is shown in figure 1. Bacteremic Vs. Nonbacteremic Melioidosis There were 102 patients in each group. The demographic characteristics and distribution of the occupational risks were similar in the two groups. Seventy patients with bacteremic melioidosis (68.6%) had diabetes mellitus, compared with 53 (52%) of the patients with nonbacteremic melioidosis Table 2. Results of the logistic regression analyses of risk factors for melioidosis and bacteremic melioidosis, with use of data for patients with community-acquired septicemia due to bacteria other than B. pseudomallei (alone or combined with data for the noninfectious control group). OR (95% CI) Risk factor Other-sepsis control group Other-sepsis and noninfectious control groups, combined Preexisting renal disease 2.6 ( ) 2.9 ( ) Thalassemic disease 11.8 ( ) 10.2 ( ) Hematologic or solid tumor 0.4 ( ) 0.4 ( ) Diabetes mellitus 4.8 ( ) 5.9 ( ) High soil and water exposure 2.6 ( ) 3.3 ( ) Moderate soil and water exposure 1.8 ( ) 2.1 ( ) Diabetes and occupation involving High soil and water exposure 6.3 ( ) 8.5 ( ) Moderate soil and water exposure 4.5 ( ) 5.6 ( )

5 412 Suputtamongkol et al. CID 1999;29 (August) Figure 1. The percentage of patients with melioidosis among the diabetics (black bars) and nondiabetics (white bars) in each occupational group (involving high, moderate, or low exposure to soil and water). (P.001). The proportion of patients with other underlying diseases or a history of previous melioidosis was similar among the bacteremic and nonbacteremic melioidosis groups. Therefore, previous melioidosis was not found to be a significant risk factor for bacteremic melioidosis in this subgroup analysis. Diabetes mellitus was the only significant factor associated with bacteremic melioidosis, in comparison with nonbacteremic melioidosis (OR, 1.32; 95% CI, ). We performed the subgroup analysis to identify risk factors for severe or bacteremic melioidosis by considering only patients with bacteremic melioidosis as the cases and only patients with community-acquired septicemia due to bacteria other than B. pseudomallei as the controls. Results of the logistic regression analysis showed that risk factors for bacteremic melioidosis were similar to those for melioidosis overall (data not shown). Discussion The proportion of patients with underlying predisposing diseases has varied from 38% to 70% in case series of melioidosis previously reported in the literature [2 5, 10]. Diabetes mellitus has been reported consistently as the most common underlying disease associated with melioidosis. Other underlying predispositions identified previously were chronic renal disease [2] and chronic alcoholic liver disease [12]. It was difficult to determine the strength of association of these concomitant diseases with melioidosis from these retrospective case series. This is the first prospective case-control study conducted specifically to determine risk factors for melioidosis and bacteremic melioidosis as well as the strength of associations. Not all patients with culture-proven melioidosis were included in the study. Some patients with severe melioidosis died before a definite diagnosis was made microbiologically on the basis of culture and therefore were not included in this study. However, the distribution of patients with melioidosis assessed by the distribution of organ involvement was similar to that reported previously [2, 5]. The proportion of all melioidosis cases that were bacteremic in this study was 50%, and the mortality in this group was also similar to that reported previously [3 5]. The distribution of other organisms causing septicemia in the infectious controls was also remarkably similar to that reported earlier from this part of Thailand [2]. Thus, both cases and infectious controls were representative of the patients with melioidosis overall and with septicemia due to other bacteria in northeastern Thailand. The second group of controls was selected randomly from among patients who were admitted with noninfectious diseases to the same hospitals. Both groups of controls were studied in order to determine whether or not the risk factors for melioidosis were different from those for septicemia caused by other organisms and those for other patients who were admitted to the hospital. Since melioidosis may be the presenting feature of diabetes, differentiation between the acute-stress hyperglycemia associated with severe sepsis and preexisting glucose intolerance was important. This study confirms that diabetes mellitus is an important risk factor for melioidosis. It is well documented that diabetic patients are more likely than nondiabetics to develop severe bacterial infections, especially with gram-negative bacteria. In areas of endemic melioidosis, diabetics were at higher risk of developing melioidosis, especially septicemic disease, than septicemia caused by other bacteria. Melioidosis affects mainly rice farmers (the most common occupation in the region) and their families. Thus, millions of the population in Thailand are at risk of contracting melioidosis. The proportion of patients with melioidosis among nondiabetic patients admitted to the hospital was similar in all occupational groups. However, among diabetic patients, rice farmers had a six to nine times higher risk of developing melioidosis than that for nondiabetics and non rice farmers. These findings demonstrate clearly the synergistic interaction between the impairment of immunity caused by diabetes mellitus and the extent of exposure to B. pseudomallei posed by working in the rice field, as risk factors for melioidosis. The prevalence of a thalassemia trait or homozygous hemoglobin E or hemoglobin E trait was 40% in these areas, but only patients with thalassemic disease such as betathalassemia/hemoglobin E or hemoglobin H disease were at a significantly higher risk of contracting melioidosis. Although thalassemia had the highest strength of association with melioidosis (i.e., patients with thalassemia were at highest risk of developing melioidosis in comparison with patients who had

6 CID 1999;29 (August) 413 other risk factors), the prevalence of thalassemia was far less than the prevalence of diabetes mellitus in this study. The prevalence of preexisting renal diseases (most commonly renal calculi) is high in northeastern Thailand [2], and this was also confirmed as an important independent risk factor for melioidosis in this study. The finding that diabetes mellitus was the only factor significantly associated with bacteremic melioidosis confirms the theory that impairment of host immunity plays a major role in the pathogenesis of melioidosis, although there was no clear explanation of the underlying mechanisms for these associations. Detailed studies to clarify the immunologic defects that predispose these patients to melioidosis are needed. Patients with solid tumors or hematologic malignancy are not protected against melioidosis but are more likely to develop septicemia caused by bacteria other than B. pseudomallei. All of them developed septicemia after chemotherapy or corticosteroid treatment. This finding indicates that neutropenia is not an important immunityimpairment cause of melioidosis. The prevention of melioidosis by health education or control measures designed to protect against exposure to B. pseudomallei in the community would be very difficult, as the organism is widely distributed in the environment. An effective vaccine may be a possible preventive measure in the future [13]. The diabetic rice farmers would be the most appropriate target population for such a trial of prevention. Acknowledgments The authors thank the directors and staffs of Sappasitprasong Hospital, Srinagarind Hospital, Srisaket Hospital, and Surin Hospital; the dean and head of the Department of Medicine, Faculty of Medicine, Siriraj Hospital, Mahidol University, for their support of this study; Dr. Wattana Laeowattana for laboratory support; Prof. Nicholas J. White and Prof. Visanu Thamlikitkul for their advice; and Ms. Julie Simpson for her statistical advice. References 1. Wuthiekanun V, Smith MD, Dance DAB, White NJ. Isolation of Pseudomonas pseudomallei from soil in northeastern Thailand. Trans R Soc Trop Med Hyg 1995;41: Chaowagul W, White NJ, Dance DAB, et al. Melioidosis: a major cause of community-acquired septicemia in northeastern Thailand. J Infect Dis 1989;159: White NJ, Dance DA, Chaowagul W, Wattanagoon Y, Wuthiekanun V, Pitakwatchara N. Halving of mortality of severe melioidosis by ceftazidime. Lancet 1989;2: Sookpranee M, Boonma P, Susaengrat W, Bhuripanyo K, Punyagupta S. Multicenter prospective randomized trial comparing ceftazidime plus co-trimoxazole with chloramphenicol plus doxycycline and cotrimoxazole for treatment of severe melioidosis. Antimicrob Agents Chemother 1992;36: Suputtamongkol Y, Rajchanuwong A, Chaowagul W, et al. Ceftazidime vs. amoxicillin/clavulanate in the treatment of severe melioidosis. Clin Infect Dis 1994;19: Rajchanuvong A, Chaowagul W, Suputtamongkol Y, Smith MD, Dance DA, White NJ. A prospective comparison of co-amoxiclav and the combination of chloramphenicol, doxycycline, and co-trimoxazole for the oral maintenance treatment of melioidosis. Trans R Soc Trop Med Hyg 1995;89: Chaowagul W, Suputtamongkol Y, Dance DA, Rajchanuvong A, Pattara- Arechachai J, White NJ. Relapse in melioidosis: incidence and risk factors. J Infect Dis 1993;168: Leelarasamee A, Bovornkitti S. Melioidosis: review and update. Rev Infect Dis 1989;11: Suputtamongkol Y, Hall AJ, Dance DAB, et al. The epidemiology of melioidosis in Ubon Ratchatani, northeast Thailand. Int J Epidemiol 1994;23: Puthucheary SD, Parasakthi N, Lee MK. Septicaemic melioidosis: a review of 50 cases from Malaysia. Trans R Soc Trop Med Hyg 1992;86: Schuckit M. Alcoholism and drug dependency. In: Fauci A, Braunwald E, Isselbecher K, et al., eds. Harrison s principles of internal medicine. 14th ed. Vol 2. New York: McGraw-Hill, 1998: Merianos A, Patel M, Lane JM, et al. The outbreak of melioidosis in the Northern Territory of Australia: epidemiology and environmental studies. Southeast Asian J Trop Med Public Health 1993;24: Bryan LE, Wong S, Woods DE, Dance DAB, Chaowagul W. Passive protection of diabetic rats with antisera specific for the polysaccharide portion of the lipopolysaccharide from Pseudomonas pseudomallei. Can J Infect Dis 1994;9:170 8.