Final answer:
The symptoms described point towards Rocky Mountain Spotted Fever (RMSF), a condition best confirmed with diagnostic testing like fluorescent antibody staining and PCR for Rickettsia rickettsii. Doxycycline is the primary treatment for RMSF.
Step-by-step explanation:
A child presenting with a salmon-colored flat rash, spiking fevers, hepatosplenomegaly, and red blood cell (RBC) laden macrophages may be indicative of Rocky Mountain Spotted Fever (RMSF), particularly if accompanied by initial cold-like symptoms that progress to a macular or papular rash. The diagnosis is confirmed using several methods such as fluorescent antibody staining, polymerase chain reaction (PCR) for Rickettsia rickettsii, and serologic testing. The primary treatment for RMSF is doxycycline, with chloramphenicol being the second-line treatment option.