8. Typical Pneumonia Atypical Pneumonia Infection caused by bacteria most common cause of community acquired pneumonia is streptococcus p neumoniae And the most common cause of Nosocomial pneumonia is staphylococcus aureus Infection caused by Mycoplasma, Chlamydia pnemoniae and viruses like RSV Influenza virus, rhinovirus ( most common cause is Mycoplasma pneumoniae . Characterized by neutrophilic infiltration and presence of intra-alveolar exudates (leading to consolidation). Characterized by lymphocytic infiltration and presence of alveolar septal and interstitial inflammation with absence of alveolar exudates Clinical features include onset high grade fever and mucopurulent cough which may also be associated with pleuritic pain. Clinical features include fever, headache and myalgia. Cough and pleural involvement is uncommon.