A 34-year-old male firefighter was diagnosed with acute stress disorder 10 days after being trapped under a collapsed beam during a structure fire in which a colleague died. At that time, he had flashbacks, nightmares, hypervigilance, emotional numbing, and derealization. He was started on supportive counseling and a short course of a sleep aid. He now presents for follow-up at 6 weeks (42 days) post-trauma. His symptoms have not improved. He continues to experience daily intrusive flashbacks of the collapse, nightly nightmares, avoidance of fire stations and any news about fires, persistent beliefs that the world is dangerous and he cannot protect anyone, emotional detachment from his family, hypervigilance, an exaggerated startle response, insomnia, and irritability. He remains unable to return to work. His counselor asks whether the ASD diagnosis should be maintained or updated. What is the most appropriate diagnostic action?