Perth melioidosis outbreak linked to contaminated saline

28 Jul 2016

Continued use of a bottle of saline to irrigate wounds for at least three months after opening it has been linked to six cases of melioidosis in suburban Perth.

This rare infection, caused by Burkholderia pseudomallei, is usually restricted to tropics but it was isolated in cellulitis on the shin and toe of a Perth patient in January 2012. The patient had not left the subtemperate southwest of the state for at least 18 years.

A cluster of five more cases emerged in December 2013. All had attended the same healthcare facility as the index case, and all had skin wounds irrigated with saline from a one litre bottle first opened three months earlier.

The organism was well-established in the bottle, where it had appeared to prosper.

The facility had continued to use the bottle despite clear instructions on the label that it should be discarded within 24 hours of opening.

A painstaking investigation, led by laboratory scientist Adam Merritt and reported in Emerging Infectious Diseases, found the organism was genotypically identical in all six cases.

“No further cases of B. pseudomallei infection occurred after removing the contaminated bottle,” Mr Merritt and colleagues said.

“This cutaneous melioido­sis cluster demonstrates that B. pseudomallei can survive and disseminate in widely used medical fluids beyond its known geographic distribution, highlighting a need to use these products according to manufacturers’ instructions.”

Despite all their efforts, the investigators could not determine how the contamination occurred, nor explain the gap between the first case and the subsequent cluster almost two years later.

“Possible explanations…include an undetected past case of chronic, unresolved cutaneous melioidosis with multiple introductions of B. pseudomallei into medical products or an external environmental reservoir common to the 2012 patient and the first, or first few, 2013 patients,” they said.

A handful of other cases of nosocomial melioidosis had been reported, but all had occurred in the tropics.

The outbreak highlighted the needs for clinicians and laboratories to be aware of possible B. pseudomallei infection, even in regions where the organism is not endemic.

“Melioidosis…is a disease with mani­festations ranging from rapidly fatal septicaemia, pneumo­nia, or meningoencephalitis to localised abscess formation, cellulitis and asymptomatic seroconversion,” they wrote.

“This disease occurs most commonly in Southeast Asia and northern Australia after exposure to contaminated soil or surface wa­ter.”

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