The investigations included a complete blood count, which revealed microcytic, normocytic anemia, a raised C-reactive protein (CRP) of 138 mg/L, negative syphilis serology (TPHA and RPR), negative bacterial and fungal cultures (pus swab), a CD4 count of 113 cells/mm3, and a viral load of 7,940,000 copies/mL, positive Gene Xpert MTB/Rif Ultra test with Rifampicin sensitivity (tissue homogenate), and a positive TB lipoarabinomannan (LAM) antigen test (urine). The gene discussed is CD4; the disease is tuberculosis.