American Board of Internal Medicine (ABIM) Certification Practice Exam

In patients who have had contact with infected aquatic environments, which organism is likely to cause infection?

1. West Nile virus

2. Mycobacterium marinum

3. Francisella tularensis

4. Zika virus

The correct answer is: Mycobacterium marinum

Mycobacterium marinum is the correct answer as it is a nontuberculous mycobacterium that is commonly associated with exposure to aquatic environments, particularly through contact with contaminated water, such as that found in swimming pools, aquariums, or natural bodies of water. This organism typically causes skin infections, often manifesting as chronic granulomatous lesions at sites of trauma or injury exposed to the water, making it a significant concern for individuals who participate in aquatic activities. In contrast, the other organisms listed are not typically linked to infections from aquatic environments. West Nile virus and Zika virus are both transmitted by mosquitoes, with lifecycles unrelated to water environments. Francisella tularensis, while it can be associated with water in some scenarios, is more commonly transmitted through contact with infected animals or environments where infected species (like rabbits) are present, rather than from aquatic sources. Thus, Mycobacterium marinum is the most relevant organism in the context of infections resulting from exposure to infected aquatic environments.