<prompt> Answer this question truthfullyWhat are the three most common causes of secondary pneumonia, and which organism is the most frequent cause?  <response>: <reason> The most common cause of secondary pneumonia is Streptococcus pneumoniae. The second and third most common causes are Haemophilus influenzae and Moraxella catarrhalis, respectively. Secondary pneumonia is a type of pneumonia that occurs as a complication of another condition, such as influenza or a respiratory infection. These three organisms are responsible for the majority of cases of secondary pneumonia, although other bacteria and viruses can also cause the condition. 