An immunosuppressed man with a military history is likely infected with which organism?

The correct choice is Strongyloides stercoralis, which is a parasitic nematode that causes strongyloidiasis. This organism is particularly significant for immunocompromised individuals, as they are at a higher risk of severe infection due to the inability of their immune systems to control the parasite. In immunosuppressed patients, Strongyloides can lead to hyperinfection syndrome, characterized by an overwhelming reaction where the parasite replicates uncontrollably, potentially causing severe gastrointestinal symptoms and disseminated disease.

Furthermore, the military history of the individual may suggest potential exposure to environments where Strongyloides is endemic, particularly in certain tropical or subtropical regions. This complements the likelihood of infection, as the life cycle of Strongyloides involves soil and can be contracted through skin contact or ingestion of larvae.

The other organisms listed are less likely to cause issues specifically in an immunocompromised host with a military background. For instance, while Trypanosoma cruzi is associated with Chagas disease, it is typically not acquired in military contexts compared to endemic regions. Naegleria fowleri, although lethal, is primarily associated with freshwater exposure rather than a particular patient history, and Paragonimus westermani,