In patients with pneumonia, higher Hb-CO levels can be measured at the onset of illness, with values decreasing to control levels after antibiotic treatment [62] . E-CO levels were reported to be higher in lower-respiratory-tract infections and bronchiectasis, with normalization after antibiotic treatment [96, 97] . Furthermore, E-CO levels in upper-respiratory-tract infections were higher than in healthy controls [74, 80] . The relationship between higher measured E-CO in these infectious states and higher Hb-CO levels cannot be concluded from these studies.