Marine injuries FAQ

I did some wreck diving this summer and got a minor abrasion on my knuckles while digging for artifacts. It was so superficial that I continued diving and didn’t give it much thought. Several weeks later, however, it doesn’t seem to be getting any better. It is red and bumpy and occasionally has some crust on it, although it doesn’t hurt. Antibiotic ointment has not helped, so I plan to see a doctor about it. Are there any marine-specific pathogens I should ask the doctor about?
While some infections might be more frequently associated with aquatic environments, there are no marine-specific pathogens, at least not to humans.
Based on your brief description, this may be an infection by an opportunistic pathogen known as Mycobacterium marinum. This organism is responsible for a condition known as aquarium granuloma. These wounds typically look like what you described: red and bumpy nodules no larger than a centimetre, usually isolated but sometimes in small clusters and not necessarily painful. There may or may not be discharge associated with the wound, and little or no improvement may follow what seems to be adequate care for the wound. This is due in part to several unique characteristics of this bacterium:
•M. marinum is an opportunistic pathogen: It causes an infection only when the right conditions (environmental and patient-related) are met. This explains why it is often not even considered as a potential culprit. It could be considered rare.
•M. marinum likes cooler temperatures, which explains why these wounds tend to flourish in areas with lower body temperatures such as hands, knuckles, elbows and knees.
•M. marinum is sensitive only to specific antibiotics, which explains why the typical antibiotic treatments are usually unsuccessful.
•M. marinum has a slow life cycle, which means treatments last a long time. Sometimes patients will abandon what could have been a successful treatment, and/or doctors may look for other potential explanations for the symptoms.
• M. marinum requires specific culture media that a doctor would not ask for unless he or she suspects this pathogen. This explains why sometimes standard culture results are negative and diagnoses are delayed.
Allow your doctor to examine the wound and follow his or her normal procedures. The doctor will probably ask you how it happened or when it started. This is where you should let him or her know about the superficial abrasion in a marine environment. You may also want to tell your doctor you read about Mycobacterium marinum (because you are a prepared and well-informed diver) and are wondering if this could be the cause. Good medical practice benefits tremendously from mutual trust and good communication. Let the doctor examine you and ask questions, and trust him or her — no dive-specific medical knowledge is needed for this type of issue.
Finally, remember to always take care of wounds and clean them thoroughly, even when they seem benign. The skin is our most effective and efficient means of immunological defence.

• — MatíasNochetto, M.D.