When an application for medical assistance hereunder is filed with a county agency, such county agency shall promptly make or cause to be made such investigation as it may deem necessary. The object of such investigation shall be to ascertain the facts supporting the application made hereunder and such other information as may be required by the rules of the state agency. Upon the completion of such investigation the county agency shall promptly determine eligibility. No approval by the county agency shall be required prior to payment for medical care provided to recipients determined to be eligible pursuant to this section.