Question: What causes Kawasaki Disease ?
Answer: The cause of Kawasaki disease isn't known. The body's response to a virus or infection combined with genetic factors may cause the disease. However, no specific virus or infection has been found, and the role of genetics isn't known. Kawasaki disease can't be passed from one child to another. Your child won't get it from close contact with a child who has the disease. Also, if your child has the disease, he or she can't pass it to another child.
Source: NHLBI

Question: How to diagnose Kawasaki Disease ?
Answer: Kawasaki disease is diagnosed based on your child's signs and symptoms and the results from tests and procedures. Specialists Involved Pediatricians often are the first to suspect a child has Kawasaki disease. Pediatricians are doctors who specialize in treating children. If the disease has affected your child's coronary (heart) arteries, a pediatric cardiologist will confirm the diagnosis and give ongoing treatment. Pediatric cardiologists treat children who have heart problems. Other specialists also may be involved in treating children who have Kawasaki disease. Signs and Symptoms The doctor will check your child for the classic signs and symptoms of Kawasaki disease. The doctor will rule out other diseases that cause similar symptoms. These diseases include Rocky Mountain spotted fever, scarlet fever, and juvenile rheumatoid arthritis. Generally, your child will be diagnosed with Kawasaki disease if he or she has a fever that lasts longer than 5 days plus four other classic signs or symptoms of the disease. However, not all children have classic signs and symptoms of Kawasaki disease. Tests and procedures can help confirm whether a child has the disease. Tests and Procedures Echocardiography If the doctor thinks that your child has Kawasaki disease, he or she will likely recommendechocardiography(EK-o-kar-de-OG-ra-fee), or echo. This painless test uses sound waves to create pictures of the heart and coronary arteries. Echo also can help show the disease's effects over time, if any, on your child's coronary arteries. Often, the disease's effects on the coronary arteries don't show up until the second or third week after the first symptoms appear. Thus, this test is done regularly after the diagnosis. Some children who have Kawasaki disease don't have the classic signs and symptoms of the acute phase. Doctors may not diagnose these children until 2 to 3 weeks after the onset of the disease. This is when another common sign of Kawasaki disease occurspeeling of the skin on the fingers and toes. If your child is diagnosed at this point, he or she will likely need echo right away to see whether the disease has affected the coronary arteries. Other Diagnostic Tests Doctors also use other tests to help diagnose Kawasaki disease, such as: Blood tests. The results from blood tests can show whether the body's blood vessels are inflamed. Chest x ray. This painless test creates pictures of structures inside the chest, such as the heart and lungs. A chest x ray can show whether Kawasaki disease has affected the heart. EKG (electrocardiogram). This simple test detects and records the heart's electrical activity. An EKG can show whether Kawasaki disease has affected the heart.
Source: NHLBI