How can an infection get into your blood stream.?

Blood stream infectn. Blood stream infections (bsi) come from many sources: 1. Iv catheters 2. Pneumonia 3. Pyelonephritis (kidney infect'n) 4. Overwhelming deep soft tissue infect'n that usual host defense mechs can't contain (severe abscess skin/pharynx/gu tract, cellulitis, tooth /gum infection..Even brushing teeth leads to transient bsi) 5. Altered defense (chemo, burn or malnutrn) allowing translocatn from gut.