Where Rocky Mountain Spotted Fever Is Most Common

Rocky Mountain Spotted Fever (RMSF)—caused by Rickettsia rickettsii and transmitted by ticks—is most frequently reported in the eastern and central United States, despite its name.

Highest Incidence Regions

• South Atlantic: North Carolina, Oklahoma, Arkansas, Tennessee, Missouri (together account for >60% of U.S. cases).
• South Central: Oklahoma, Arkansas, Texas.

Also Present in the West

• Montana, Idaho, Washington, Oregon, California, Arizona — but at lower rates.
• The Rocky Mountain wood tick (Dermacentor andersoni) is the primary vector in the West; the American dog tick (D. variabilis) dominates in the East.

Habitat & Seasonality

• Habitat: Wooded areas, grassy fields, brushy edges, trails—where ticks quest on vegetation.
• Season: Peak transmission April–September (nymph/adult tick activity).

Key Point

RMSF is a nationwide risk (cases reported in nearly every state), but the highest burden is in the mid-South and Southeast, not the Rocky Mountains. Early doxycycline treatment is lifesaving.