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Seasonal variation of viral respiratory infections by month. Hatched squares = controls; open squares = COPD; A = adenovirus; C = coronavirus; CMV = cytomegalovirus; E = enterovirus; F = influenza virus A or B; P = parainfluenza virus type 1, 2, or 3; R = rhinovirus; RS = respiratory syncytial virus. Dual viral infections are designated with backslash (/). Circles signify hospitalizations. (Reprinted with permission from Am J Respir Crit Care Med.6)
