Leg clots occur without warning with sudden pain and swelling in a leg muscle, usually the calf. This is a particularly dangerous condition because the clot can break lose from the veins in the leg, travel to the lungs and block blood flow to kill a person. In a report in the British medical journal, Lancet , doctors at the London School of Hygiene and Tropical Medicine showed that infections may cause sudden clotting in the leg muscles called Deep Vein Thrombosis. They showed a 20 percent increase in infections, particularly urinary and respiratory, one to two weeks before a person develops clots. This report supports the current theory of inflammation causing heart attacks, strokes, and clotting. Your immunity is good because it is supposed to kill germs when they enter your body. However, if your immunity keeps on being active, it attacks your own body to damage arteries and other tissues.
People at the highest risk for clots are those who are sedentary for a long time, such as in long distance plane flights, and those who suffer cancers. Since infections are common and deep vein clots are not, you should not worry about clots every time you get an infection. However, if after a urinary or respiratory infection, you suffer sudden pain in a leg without any other explanation, check with a doctor immediately to rule out a clot. Journal reference