What type of doctor can order a rapid step test?

Any doctor. (assuming "step" is a typo for "strep") - any doctor can order the test but it is most often ordered by primary care doctors (pediatrician, internist, family physician) or by the er. The test is helpful for determining if a sore throat is viral and won't respond to antibiotics or due to strep which requires treatment both for relief and to avoid the risk of rheumatic fever.