Pneumonia is caused by the bacteria Diplococcus pneumoniae which infects the alveoli of lungs. It generally spreads through the sputum of patient. Fever, cold and difficulty in breathing are some common symptons of pneumonia. Common cold is caused by a variety of viruses, most commonly by rhinovirus (RNA virus). It spreads through droplet infection. It affects the upper respiratory tract but not the lungs. Nasal and bronchial irritation, sneezing and coughing are some common symptoms of cold.