CD4 and infection: However, to allow the natural history of GUD to vary by HIV status, we would have had to estimate the degree of coinfection, factoring in the epidemiological association between the two infections due to shared risk factors and biological effects of each infection on the other,13 91 92 and considered the effect of CD4 count and antiretroviral therapy status on GUD.90 This would have added in complexity and thus uncertainty, and ultimately we erred on the side of underestimating rather than overestimating GUD burden.