Atypical mycobacterial cutaneous infections in Hong Kong: 10-year retrospective study

To review the epidemiology of atypical mycobacterial cutaneous infection in Hong Kong.

Retrospective study.

Social Hygiene Service (Dermatology Division), the largest dermatological referral centre in Hong Kong.

Patients with a diagnosis of atypical mycobacterial cutaneous infection based on clinical features, histopathology, with or without a positive culture during the period 1993 to 2002.

Epidemiological data, clinical features, histology, microbiological investigation, and treatment response.

Of 345,394 dermatological cases presented over the 10-year period, 33 (0.0096%) cases (19 male, 14 female) of atypical mycobacterial cutaneous infection were diagnosed. The most common type of infection was caused by Mycobacterium marinum (n=17, 51.5%), followed by Mycobacterium avium-intracellulare (n=3, 9.1%) and Mycobacterium chelonae (n=2, 6.1%). The upper limb, especially the hands and fingers, was the most common (69.7%) site of involvement. Tissue culture was positive in 18 (54.5%) cases. All biopsies showed granulomatous histology. Thirty-two patients received treatment and 31 responded. Twenty-six were treated with oral tetracycline group of antibiotics (minocycline, doxycycline, tetracycline). The duration of treatment ranged from 8 to 54 weeks (mean, 24 weeks). Mild transient adverse effects to treatment were reported in six cases.

Atypical mycobacterial infection is rare in Hong Kong. Because of the low sensitivity of traditional culture techniques, atypical mycobacterial infection may be underdiagnosed if only culture-confirmed cases are included. Polymerase chain reaction provides a rapid and sensitive method to improve diagnostic accuracy. Tissue culture is crucial to determine antimicrobial susceptibility. In our study, tetracycline group of antibiotics, especially minocycline, was an effective treatment, particularly in cases caused by Mycobacterium marinum.