CTF is seasonal, mostly occurring in the Rocky Mountain region of the United States and usually in altitudes from 4,000 to 10,000 feet (1.600 to 3.000 meters). Patients with CTF are mostly campers and young males, who most likely have been bitten because of their  activities. Cause
Virology
The virus particle, like other coltiviruses, is about 80 nm in diameter and is generally not enveloped. The double-stranded RNA viral genome is about 20,000 bp long and is divided into 12 segments, which are termed Seg-1 to Seg-12. Viral replication in infected cells is associated with characteristic cytoplasmic granular matrices. Evidence suggests the viral presence in mature erythrocytes is a result of replication of the virus in hematopoetic erythrocyte precursor cells and simultaneous maturation of the infected immature cells rather than of direct entry and replication of CTFV in mature erythrocytes. Tick
The Rocky Mountain wood tick is usually found attached to a host, but when it is without a host, it hides in cracks and crevices, as well as soil. If for some reason the tick is not able to find a host before the winter, it will stay under groundcover until spring, when it can resume its search. The wood tick does not typically seek hosts in the hottest summer months. Adult ticks tend to climb to the tops of grasses or low shrubs, attaching themselves to a host wandering by. They secure the attachment by secreting a cement-like substance from their mouths, inserting it into the host. Transmission
Colorado tick fever is acquired by tick bite.
More advanced imaging techniques can be used if the clinical picture is unclear; the exact role of different imaging modalities remains uncertain. Some studies have demonstrated findings on magnetic resonance imaging (MRI scan) that can differentiate between septic arthritis and transient synovitis (for example, signal intensity of adjacent bone marrow). Skeletal scintigraphy can be entirely normal in transient synovitis, and scintigraphic findings do not distinguish transient synovitis from other joint conditions in children. CT scanning does not appear helpful. Differential diagnosis
Pain in or around the hip and/or limp in children can be due to a large number of conditions. Septic arthritis (a bacterial infection of the joint) is the most important differential diagnosis, because it can quickly cause irreversible damage to the hip joint. Fever, raised inflammatory markers on blood tests and severe symptoms (inability to bear weight, pronounced muscle guarding) all point to septic arthritis, but a high index of suspicion remains necessary even if these are not present. Osteomyelitis (infection of the bone tissue) can also cause pain and limp.Bone fractures, such as a toddlers fracture (spiral fracture of the shin bone), can also cause pain and limp, but are uncommon around the hip joint. Soft tissue injuries can be evident when bruises are present. Muscle or ligament injuries can be contracted during heavy physical activity —however, it is important not to miss a slipped upper femoral epiphysis. Avascular necrosis of the femoral head (Legg-Calvé-Perthes disease) typically occurs in children aged 4–8, and is also more common in boys.