Fishing for a Diagnosis, the Impact of Delayed Diagnosis on the Course of Mycobacterium marinum Infection: 21 Years of Experience at a Tertiary Care Hospital.

Background: Mycobacterium marinum is a common but underreported mycobacterial infection. We conducted a large retrospective study to determine risk factors and describe the therapeutic interventions and outcomes in patients with uncomplicated and complicated M. marinum infection.

Methods: Culture-confirmed M. marinum infection cases were identified from the Mayo Clinic Clinical Mycology Laboratory from January 1998 to December 2018. Complicated M. marinum infection was defined as the presence of tenosynovitis, septic arthritis, or osteomyelitis. Differences in complicated vs uncomplicated M. marinum infections were analyzed using statistical comparisons.

Results: Twelve cases had a complicated M. marinum infection. Patients with a complicated infection were older (64.3 ± 11.1 vs 55.8 ± 14.5; P  = .03), had longer duration of symptoms (5 vs 3 months; P  = .011), and had more surgical debridements (1 vs 0; P  < .001). Length of treatment and number of drugs used were not statistically significant. Complicated M. marinum cases received more medications (2 vs 1; P  = .263) and were treated longer (5.7 vs 3.5 months; P  = .067). Antibiotic susceptibilities were performed in 59% of the patients. All isolates were susceptible to clarithromycin. From the tetracyclines, doxycycline had a better susceptibility pattern.

Conclusions: M. marinum infection is an important cause of skin and soft tissue infection. Poor water exposure documentation, unusual clinical presentation, and empiric antibiotic treatment before definitive M. marinum diagnosis often contribute to a delayed diagnosis. Complicated M. marinum cases had longer duration of symptoms and more surgical debridements. No difference in the number of drugs used or clinical outcome was observed.