What is the issue?
Mycobacterium ulcerans (M. ulcerans) is a bacterial infection which causes slowly developing painless nodules or papules which can become destructive skin ulcers. These are variously known as the Bairnsdale or Buruli ulcer.
Mycobacterium ulcerans infection has been known in the Frankston and Mornington Peninsula area since the 1990s. However since 2009 there has been a steady increase in notifications which – although still limited – warrants increased awareness and testing of possible cases. There have been over 100 confirmed cases over the last five years, mostly in residents in Frankston and surrounding suburbs, and on the Mornington Peninsula, particularly Rye, Sorrento, Blairgowrie and Portsea. Most of these cases are residents, however M. ulcerans has also been diagnosed in visitors to these areas.
Delays in diagnosis often occur following initial presentation. Early diagnosis and treatment is essential to minimise tissue damage.
Who is at risk?
Everyone is susceptible to infection. Although the exact reservoir is unclear the organism appears to be associated with swampy or stagnant water, and/or coastal vegetation. Individuals who visit or frequent these areas are therefore considered at greater risk. M. ulcerans is not known to be transmitted from one person to another. People aged 60 years and over have a higher rate of notification with M. ulcerans in Victoria.
Symptoms and transmission
Although the incubation period has not been clearly defined, it is thought to vary from weeks to several months, with a median of 4-5 months. There is a peak in diagnoses in Victoria between June and November each year, however cases are diagnosed year round.
The first sign of M. ulcerans infection is usually a painless, non-tender nodule or papule. It is often thought to be an insect or spider bite and is sometimes itchy. The lesion may occur anywhere on the body but it is most common on exposed areas of the limbs. In one or two months the lesion may become fluctuant and ulcerate, forming a characteristic ulcer with undermined edges. Ordinarily there is no regional lymphadenopathy, fever or systemic manifestations. If left untreated extensive ulceration can occur, requiring surgical management. Occasionally the disease may present as a firm, painless elevated plaque or an entire limb or area may be indurated by oedema without an ulcer.
Making a diagnosis
Dry swabs (or pre-moistened with sterile saline) from beneath the undermined edges of the lesion or a biopsy should be sent for staining for acid-fast bacilli (AFBs), PCR and culture. Although the same swab or biopsy may be used for all three procedures if performed in the same laboratory, it is recommended to send two separate swabs or a swab and a biopsy, especially if a specimen is being referred to the Victorian Infectious Diseases Reference Laboratory (VIDRL) for culture and PCR. It is essential that there is visible clinical material on the swab. Please state on the request form that M. ulcerans is suspected. A positive smear for AFBs makes the diagnosis likely. Culture or PCR is required for confirmation. A negative smear does not exclude the diagnosis.
A biopsy of suspicious lesions which have not ulcerated can be sent for histology. The suspected diagnosis should be mentioned and a request made for AFB staining, specific PCR and mycobacterial culture. The PCR test is only performed at VIDRL and can confirm the diagnosis in a few days. Culture usually takes 8–12 weeks.
Under the Public Health and Wellbeing Regulations 2009, M. ulcerans infection is a Group B disease and must be notified in writing by medical practitioners and persons in charge of laboratories within five days of diagnosis.
Simple precautionary measures such as wearing appropriate protective clothing when gardening and undertaking recreational activities in identified risk areas may assist in preventing infection. Cuts and abrasions should be cleaned promptly and exposed skin contaminated by suspect soil or water should be washed following outdoor activities. Although not confirmed, it is possible that M. ulcerans may be transmitted by mosquito bites, therefore the use of insect repellent when outdoors during warmer months is recommended.
Referral for treatment to doctors experienced in the management of this condition is recommended. The current mainstay of treatment is rifampicin-containing combination oral antibiotic therapy. Surgery may be used in combination with antibiotic therapy where indicated.