Extremely rarely. An IUD (intra-uterine device) is a very effective method of contraception. Though their reputation for causing infection still exists from cases many decades ago, currently iuds are very safe. It is very rare for an IUD to cause sepsis (a uterine infection that spreads into the blood and throughout the body).
Yes... But rarely do they cause infection unless they become dislodged and perforate the uterus. They can serve as a focus of ongoing infection if the uterus becomes infected - but simply removing the iud usually resolves this without a problem.