To the Editor: A 79-year-old man from Gatton, 80 km west of Brisbane (Box 1), presented in July 2008 with an extensive area of cellulitis on the right knee surrounding a central ulcer 2 cm in diameter (Box 2).

Gram staining of swabs taken from the ulcer showed polymorphs and gram-negative bacilli. An oxidase-positive, gentamicin-resistant, gram-negative bacillus was cultured. It had the biochemical profile and characteristic colonial morphology of Burkholderia pseudomallei, the causative organism of melioidosis. The identity of the organism was confirmed by polymerase chain reaction. Blood and urine cultures were negative, and a chest x-ray was normal.

The patient was treated with intravenous ceftazidime 2 g four times a day for 10 days, as well as oral cotrimoxazole 320/1600 mg twice a day for 6 months. The infection appeared to be localised, and the patient made a successful recovery.

Melioidosis can have a wide spectrum of clinical manifestations.1 Skin and soft tissue infections, as seen in our patient, may lead to fulminating systemic infections if treatment is inadequate.1 There were also several factors that predisposed our patient to melioidosis, including type 2 diabetes, renal impairment, and concurrent steroid treatment (for persistent sinusitis).

The patient had a history of recent local exposure to floodwaters and soil: he had spent several hours kneeling in wet mud repairing a burst water pipe. Within a few days, an abrasion on the knee had developed into the presenting lesion. The patient denied visiting any areas where tropical melioidosis was endemic.

In Australia, melioidosis is generally considered endemic in areas north of 20°S. In subtropical Australia, below 20°S, sporadic endemic infections in domestic animals and humans have occurred in south-eastern Queensland2-6 and south-western Western Australia.7 Three fatal human cases have been reported from the Brisbane River valley (two in 1996, near a reservoir 20 km north of Gatton;4 one in 1999, 5 km from Ipswich city centre5). All three patients were exposed to floodwaters, two had infected skin lesions, and all three progressed to fulminating pneumonia. All three also had alcohol-associated pathology, a recognised comorbidity.1 There were also two less well documented (but apparently local) human cases from the Brisbane region in 19676 and 1974.4

Recent molecular typing of five strains of B. pseudomallei isolated from south-eastern Queensland showed them to be genetically distinct from each other and from isolates obtained from tropical Australia, suggesting that this subtropical focus is most likely a natural phenomenon from ancient times.5

The reticulated water supply to our patient’s house was sourced from the Wivenhoe Dam. The source of the bacteria was most likely the local soil, which is of a heavy clay type suitable for this organism. The Brisbane River valley appears to be a subtropical endemic area for melioidosis, and further sporadic cases can be expected.

1 Location of melioidosis cases reported in Queensland

2 Area of cellulitis around a central ulcer on the patient’s right knee