Efficacy of Azithromycin Plus Doxycycline Versus Doxycycline Plus Placebo in Patients With Rocky Mountain Spotted Fever

Inclusion Criteria: * Any gender * Over 18 years old * hospitalized in the internal medicine service, emergency department or intensive care unit of Hospital General de Mexicali (ISESALUD) or Hospital General Zona No. 30 (IMSS) with suspicion of RMSF that present fever and 2 or more of the next symptoms: headache, myalgia, rash, nausea, pharyngeal hyperemia, vomiting, abdominal pain, neurological disorders. * In addition to at least one of the next epidemiologycal fators: presence of vectors in areas of residence or endemic areas visited two weeks prior to the onset of symptoms, history of visiting or residing in areas with RMSF transmission in the last two weeks, existence of confirmed cases in the locality of origin, history of vector bite or contact with dogs in the two weeks. Exclusion Criteria: * Other clinical suspicion rather than RMSF * History of allergy to doxycycline, azithromycin, bean starch or bovine gelatin. * Not signing the informed consent * Pregnancy.