Which organism is most likely to cause the symptoms described in a patient with a recent splenectomy and a negative Plasmodium PCR?

In the context of a patient who has recently undergone splenectomy, Babesia microti is the organism most likely to cause symptoms due to its association with infections in individuals who are asplenic or have impaired splenic function. The spleen plays a crucial role in filtering the blood and mounting an immune response to certain pathogens, especially encapsulated organisms and blood parasites.

Babesia microti is a protozoan parasite transmitted by ticks, primarily responsible for causing babesiosis, which can lead to symptoms such as fever, chills, and hemolytic anemia. Patients without a spleen are at a heightened risk for severe disease caused by this organism due to the lack of the spleen's protective immune functions.

A negative Plasmodium PCR rules out malaria, which is another tick-borne illness that can affect individuals with asplenia. Since Babesia is related and can present similarly, it is a strong contender. In contrast, the other organisms listed—Bartonella bacilliformis, Bordetella bronchiseptica, and Brucella—are less commonly associated with infections in asplenic patients, and their disease profiles do not align as closely with the immediate post-splenectomy infection risks. Therefore, Bab