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Nursing and public health aspects of Mycobacterium marinum

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VOL: 96, ISSUE: 44, PAGE NO: 41

Helen Perfect, RGN, is dermatology specialist nurse, Amersham Hospital, Buckinghamshire

The first time that Mycobacterium marinum was isolated was in 1926 in saltwater fish that had died in an aquarium. In 1942 this mycobacterium was found to be causing tuberculosis in freshwater platyfish in Mexico. Despite this, it was not recognised as a cause of human disease until 1951 when it was isolated in the lesions of swimmers in a swimming pool in Sweden - thus the term ‘swimming pool granuloma’ was coined.

 

The first time that Mycobacterium marinum was isolated was in 1926 in saltwater fish that had died in an aquarium. In 1942 this mycobacterium was found to be causing tuberculosis in freshwater platyfish in Mexico. Despite this, it was not recognised as a cause of human disease until 1951 when it was isolated in the lesions of swimmers in a swimming pool in Sweden - thus the term ‘swimming pool granuloma’ was coined.

 

 

As well as swimming pools, the infection can be acquired from ocean beaches, natural pools, rivers, lakes and old wells which may harbour the mycobacterium in cracks in the masonry. In 1962, the first cases of M. marinum skin infection from a tropical fish tank were found.

 

 

Aetiology
The natural habitat for M. marinum is water, in particular water that is not often replenished. It is prevalent in heated water in temperate climates, including the sea. It is found in diseased fish, masonry crevices and in mud.

 

 

It has also been isolated in chlorinated water. Beurey et al (1981) noted that increasing chlorination from 0.2mg/l to 0.5mg/l caused the mycobacterium to disappear.

 

 

Clinical features
M. marinum is only pathogenic on skin that has been abraded. The incubation period can vary from one week to two months, but infection usually becomes evident two to three weeks following exposure to contaminated water.

 

 

The eruption may begin as a single papule or a group of papules. These lesions may break down to form a crusted ulcer or a suppurating abscess, but the eruptions may also remain as warty lesions. Nodules along the line of lymphatic drainage are not uncommon, and the regional lymph glands may be slightly enlarged (Loria, 1976). Widespread lupoid lesions have been known to occur.

 

 

There is a tendency to spontaneous healing within a few months and almost all lesions will have healed in one to three years.

 

 

Lesions are common on the hands and fingers of fish fanciers, as they seldom appreciate the risk of M. marinum infection. They are particularly at risk if they have any cuts or lesions on their hands, fingers or wrists. Simple precautions, such as wearing gloves, could considerably reduce the incidence of infection (Grey et al, 1990).

 

 

There should be stringent public health supervision of public swimming pools, with observation for defective tiles or cement surrounds. Badly maintained swimming pools can provide a suitable habitat for the growth of M. marinum and the risk of infection can be greatly reduced by the correct chlorination of swimming pools. Samples of water should be taken from swimming pools at regular intervals and tested to identify any contamination.

 

 

Diagnosis and treatment
If there is a link between the onset of a skin infection and the patient’s hobby - such as fish fancier or swimmer - M. marinum may be indicated. The clinical history supported by a cultural identification, by aspiration, biopsy or direct smear of pus may provide a means of diagnosis. Histology reports generally demonstrate non-specific inflammation in the first months, while older lesions show granuloma formation.

 

 

There is no absolute consensus on a treatment regimen for this condition. The application of topical creams such as clotrimazole or fluocinolone have in some patients been of no effect and have even exacerbated the infection (Littlejohn and Dixon, 1984). Heat has been found to be beneficial in some cases, and it has also been suggested that M. marinum is unable to grow in temperatures above 37°C.

 

 

Antibiotic therapy may be beneficial, falling into three classes (Collins et al, 1985; Black and Erkyn, 1977; Aria et al, 1984):

 

 

- Rifampicin used in conjunction with another drug, often ethambutol;

 

 

- Co-trimoxazole;

 

 

- Tetracycline, especially minocycline.

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