In a 2004 investigation into adverse effects associated with infliximab and etanercept, M. tuberculosis was observed to be the most frequent cause of infections, but a later study looking at non-viral infections across all TNF inhibitors found that it had dropped to third place (59% to 12.5%) (Wallis et al., 2004; Baddley et al., 2014). This evidence concerns the gene TNF and infection.