Using modelling and simulation to account for these shortcomings, we estimated the M tuberculosis BSI prevalence to be 45% (95% CI 38–52) in patients with HIV-associated tuberculosis with WHO danger signs who have a median inpatient CD4 count of 76 cells per μL if two blood cultures are taken, with the prevalence increasing at lower CD4 cell counts. The gene discussed is CD4; the disease is tuberculosis.