Why was virus culture done after Gram and acid-fast stain results were obtained

A 40 year old man who was seropositive for HIV experienced abdominal pain, fatique, and low grade fever (38 degree C) for 2 weeks. A chest X-ray exam revealed lung infiltrates. Gram and acid fast stains were negative. A viral culture revealed the cause of his symptoms: a large , enveloped polyhedral virus with double-stranded DNA. What is the disease? Which virus causes it? Why was virus culture done after Gram and acid-fast stain results were obtained