Nicholas M. Anstey

Endemic Melioidosis in Tropical Northern Australia: A 10-Year Prospective Study and Review of the Literature

In a prospective study of melioidosis in northern Australia, 252 cases were found over 10 years. Of these, 46% were bacteremic, and 49 (19%) patients died. Despite administration of ceftazidime or carbapenems, mortality was 86% (43 of 50 patients) among those with septic shock. Pneumonia accounted for 127 presentations (50%) and genitourinary infections for 37 (15%), with 35 men (18%) having prostatic abscesses. Other presentations included skin abscesses (32 patients; 13%), osteomyelitis and/or septic arthritis (9; 4%), soft tissue abscesses (10; 4%), and encephalomyelitis (10; 4%). Risk factors included diabetes (37%), excessive alcohol intake (39%), chronic lung disease (27%), chronic renal disease (10%), and consumption of kava (8%). Only 1 death occurred among the 51 patients (20%) with no risk factors (relative risk, 0.08; 95% confidence interval, 0.01-0.58). Intensive therapy with ceftazidime or carbapenems, followed by at least 3 months of eradication therapy with trimethoprim-sulfamethoxazole, was associated with decreased mortality. Strategies are needed to decrease the high mortality with melioidosis septic shock. Preliminary data on granulocyte colony-stimulating factor therapy are very encouraging.

A new NOS2 promoter polymorphism associated with increased nitric oxide production and protection from severe malaria in Tanzanian and Kenyan children

BACKGROUND Nitric oxide (NO) is a mediator of immunity to malaria, and genetic polymorphisms in the promoter of the inducible NO synthase gene (NOS2) could modulate production of NO. We postulated that NOS2 promoter polymorphisms would affect resistance to severe malaria. METHODS We assessed genomic DNA from healthy children and from those diagnosed with malaria from Tanzania (n=47 and n=138, respectively) and Kenya (n=1106) for polymorphisms by single-stranded conformational polymorphism (SSCP) analysis and sequencing. We also measured in-vivo NO production in Tanzanian children. FINDINGS We identified a novel single nucleotide polymorphism, -1173 C-->T, in the NOS2 promoter that was significantly associated with protection from symptomatic malaria (odds ratio 0.12, 95% CI 0.03-0.48, p=0.0006) in 179 Tanzanian children, and significantly associated with protection from severe malarial anaemia (adjusted relative risk 0.25, 95% CI 0.09-0.66, p=0.0005) in 1106 Kenyan children studied over 5 years. The risk of parasitaemia was not significantly different in wild-type or -1173 C-->T individuals. -1173 C-->T protection in Tanzanians was independent of the previously recognised NOS2-954 G-->C polymorphism. The (CCTTT)(n) NOS2 polymorphism (Tanzania and Kenya) was not associated with severe malaria outcomes. -1173 C-->T was associated with increased fasting urine and plasma NO metabolite concentrations in Tanzanian children, suggesting that the polymorphism was functional in vivo. Interpretation The NOS2 promoter -1173 C-->T single nucleotide polymorphism is associated with protection against cerebral malaria and severe malarial anaemia. Increased NO production in individuals with the -1173 C-->T polymorphism lends support to a protective role for NO against these syndromes. Targeted interventions to increase NO delivery or production could provide novel preventive and therapeutic strategies against these major causes of mortality in African children.

Melioidosis: acute and chronic disease, relapse and re-activation

In melioidosis-endemic regions the importance of re-activation of Burkholderia pseudomallei from latent foci remains unclear. This topic was assessed in a 10-year prospective study (1989-99) of melioidosis in the tropical north of the Northern Territory of Australia, together with other aspects of the nature of melioidosis. Incubation period from defined inoculating events was previously ascertained as 1-21 (mean 9) days. Of 252 total cases 244 (97%) were considered to be from recent acquisition of B. pseudomallei infection and 8 (3%) were considered to be re-activation from a latent focus. Acute illness occurred in 222 (88%) cases; 30 (12%) cases had chronic illness (symptomatic for > 2 months). Of the 207 patients surviving the initial illness, 27 (13%) had a confirmed relapse (mean time from initial diagnosis of 8 months), with 5 relapsing twice. Of these 32 relapses, 15 (3 fatal) were associated with poor adherence to the eradication therapy antibiotics and 10 (none fatal) were failures of eradication with doxycycline monotherapy. Following initial intensive therapy with ceftazidime or meropenem for at least 14 days, eradication therapy with trimethoprim-sulphamethoxazole monotherapy for at least 3 months had been more successful.

Low plasma arginine concentrations in children with cerebral malaria and decreased nitric oxide production

Nitric oxide (NO) production and mononuclear cell NO synthase 2 (NOS2) expression are high in healthy Tanzanian children but low in those with cerebral malaria. Factors that downregulate NOS2 also diminish factors involved in cellular uptake and biosynthesis of L-arginine, the substrate for NO synthesis. We therefore postulated that L-arginine concentrations would be low in individuals with cerebral malaria. We measured concentrations of L-arginine in cryopreserved plasma samples from Tanzanian children with and without malaria. L-arginine concentrations were low in individuals with cerebral malaria (mean 46 micromol/L, SD 14), intermediate in those with uncomplicated malaria (70 micromol/L, 20), and within the normal range in healthy controls (122 micromol/L, 22; p<0.0001). Analysis by logistic regression showed that hypoargininaemia was significantly associated with cerebral malaria case-fatality. Hypoargininaemia may contribute to limited NO production in children with cerebral malaria and to severe disease.

Melioidosis epidemiology and risk factors from a prospective whole-population study in northern Australia

Objectives  The aims of this study were to describe the epidemiology of melioidosis in tropical northern Australia and to assess the importance of defined risk factors.

Adjunctive Granulocyte Colony-Stimulating Factor for Treatment of Septic Shock Due to Melioidosis

Melioidosis, caused by the intracellular pathogen Burkholderia pseudomallei, is endemic in northern Australia and Southeast Asia. Risk factors for this infection have also been associated with functional neutrophil defects. Because of this, granulocyte colony-stimulating factor (G-CSF) was adopted for use in patients with septic shock due to melioidosis in December 1998. We compared the mortality rates from before and after the introduction of G-CSF therapy at the Royal Darwin Hospital (Darwin, Australia) during the period of 1989-2002. The mortality rate decreased from 95% to 10% after the introduction of G-CSF. Risk factors, the duration of illness before presentation, and the severity of illness were similar in both groups. A smaller decrease in mortality among patients in the intensive care unit who did not have melioidosis was observed, suggesting that other changes in management did not account for the magnitude of the benefit seen. We conclude that G-CSF may have contributed to the reduction in the mortality rate among patients with septic shock due to melioidosis.

Outcomes of Patients with Melioidosis Treated with Meropenem

ABSTRACT Melioidosis, an infection due to Burkholderia pseudomallei, is endemic in southeast Asia and northern Australia. We reviewed our experience with meropenem in the treatment of severe melioidosis in 63 patients over a 6-year period. Outcomes were similar to those of ceftazidime-treated patients (n = 153) despite a deliberate selection bias to more-unwell patients receiving meropenem. The mortality among meropenem-treated patients was 19%. One patient had a possible drug fever associated with the use of meropenem. We conclude that meropenem (1 g or 25 mg/kg every 8 h intravenously for ≥14 days) is an alternative to ceftazidime and imipenem in the treatment of melioidosis. The use of meropenem may be associated with improved outcomes in patients with severe sepsis associated with melioidosis.

A proposed scoring system for predicting mortality in melioidosis

Melioidosis, due to infection with the environmental organism Burkholderia pseudomallei, continues to be associated with high mortality despite improvements in antibiotic therapy. Using simple clinical findings and baseline laboratory tests available at the time of admission, we attempted to define those patients with acute melioidosis who were at higher risk of death. Using data, collected prospectively from the period October 1989 to June 2002, from patients with acute culture-confirmed melioidosis presenting at the Royal Darwin Hospital, Darwin, Australia, a number of variables were selected that were easily available at the time of admission and reflected organ dysfunction. Mortality was predicted in univariate logistic and multivariate models by the presence of pneumonia, age at diagnosis, serum urea, serum bilirubin, lymphocyte count, and serum bicarbonate. A score was assigned from 0 to 2, based on the degree of abnormality. A melioidosis score was formed from the sum of these scores, with a maximum score of 11. A score of < or = 3 (n = 140) was associated with a mortality of 8.6%, whereas a score of > or = 4 (n = 112) was associated with a mortality of 44.6%. Although this scoring system requires external validation, it may help identify a suitable target group of patients for intensive intervention such as early admission to an intensive care unit, the early use of meropenem, and goal-directed resuscitation therapies.

Increased nitric oxide production in acute diarrhoea is associated with abnormal gut permeability, hypokalaemia and malnutrition in tropical Australian aboriginal children

Australian Aboriginal children hospitalized with diarrhoeal disease have severe manifestations with acidosis, hypokalaemia, osmotic diarrhoea and abnormal small bowel permeability. Nitric oxide (NO) production is increased in diarrhoeal disease, but its relationship to mucosal function and diarrhoeal complications is not known. We examined the relationship between NO production and complications of acute diarrhoea in Aboriginal and non-Aboriginal children between February 1998 and February 2000. We enrolled 318 children admitted to Royal Darwin Hospital into one of three groups: acute diarrhoea, non-diarrhoeal controls with no inflammatory illness, and non-diarrhoeal controls with inflammatory illness. Nitric oxide production was measured by urine nitrate-creatinine (NOx/Cr) excretion on a low nitrate diet. Small bowel intestinal permeability was measured by the lactulose-rhamnose (L/R) ratio on a timed blood specimen. The NOx/Cr ratios were markedly elevated in Aboriginal diarrhoeal cases (geometric mean [GM] = 1.23, 95% confidence interval [95% CI] 1.07-1.44), lowest in non-Aboriginal non-inflammatory controls (GM = 0.13, 95% CI 0.10-0.16) and intermediate in all other groups (GM = 0.35, 95% CI 0.28-0.43). Convalescent levels (day 5) in the Aboriginal diarrhoeal group (GM = 1.02, 95% CI 0.82-1.28) were slower to fall than L/R ratios. Multivariate analysis in the diarrhoeal group indicated that high NO production was associated with abnormal permeability, hypokalaemia and malnutrition, but not with the severity of diarrhoea, acidosis or osmotic diarrhoea. We concluded that increased NO production may contribute to impaired mucosal barrier function and hypokalaemia in acute gastroenteritis, which may be the cost of the known gut-protective and antimicrobial effects mediated by NO in acute intestinal inflammation.