Rashid , Muhammad Noman, et al. “Evaluation of Atypical Bacteria Involved in Recurrent Deterioration of Symptoms in Chronic Obstructive Pulmonary Disease”. Journal of Liaquat University of Medical & Health Sciences, vol. 20, no. 5, Jan. 2022, pp. 335-40, http://121.52.154.205/index.php/jlumhs/article/view/547.