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Clinical news

Negative tests for Mycobacterium ulcerans disease: caution urged

By Kate Murchison
Health practitioners should be cautious when interpreting initial negative polymerase chain reaction (PCR) results from patients with lesions suggestive of Mycobacterium ulcerans disease (Buruli ulcer), Australian researchers have reported in the Medical Journal of Australia.

In their analysis of data from 551 patients at Barwon Health, Victoria, with prospectively confirmed M. ulcerans disease between 1998 and 2018, they found that PCR tests for the initial swab specimen were negative in 34 cases, but positive on repeat PCR samples. Fifteen of the repeat samples were punch biopsy specimens and 19 were swab specimens. The initial false-negative test led to a diagnostic delay of up to 74 days and was associated with early lesions and lesions in children.

‘It is imperative that swab samples are taken by circling the entire undermined edge of a lesion, and checking that clinical material from the lesion is visible on the swab surface’, the researchers wrote, noting that incorrect swabbing technique probably explained most of the negative initial PCR results.

A biopsy, for fresh tissue, or fine-needle aspiration, for tissue fluid, was needed for nonulcerative lesions, they added.
Med J Aust 2019; doi: 10.5694/mja2.50046.