Christ-Cain and Mueller nicely performed three randomized studies to assess if a PCT-based therapeutic strategy (based on serum PCT concentrations as follows: antibiotic strongly discouraged when less than 0.1 ng/mL; discouraged when less than 0.25 ng/mL; encouraged when greater than 0.25 ng/mL; strongly encouraged when greater than 0.5 ng/mL) could reduce antibiotic use in lower respiratory tract infections (Christ-Crain et al. 2004). This evidence concerns the gene CALCA and Recurrent lower respiratory tract infections.