Suppose that 0.5% of all people have a disease. There is testing available for this disease. If the person being tested has the disease, the test will always return positive. However, if the person being tested does not have the disease, the test will return negative 98% of the time and return positive the rest of the time. If I randomly choose a person and they test positive, what is the probability that they actually have the disease? Express your answer as a common fraction.