Pneumonia is an inflammatory condition within the lungs produced as a result of infection that primarily affects the alveoli. Generally it is caused by viral or bacterial infections and also by some autoimmune diseases that causes the inflammation. The common signs off pneumonia include fever, chills, productive cough and chest pain. Pneumonia is generally classified into two types – community acquired pneumonia and nosocomial (hospital acquired) pneumonia. In the former case the causative pathogens are primarily viruses and gram positive bacteria while in the later case the causative pathogens are primarily gram negative organisms. The most common bacteria involved are Streptococcus pneumoniae, Staphylococcus aureus, Escherichia coli, and Haemophilia influenzae. Sometimes in typical hospital acquired pneumonia there is involvement of Pseudomonas sp. too. If untreated the bacteria can gain access to the blood vessels and lead to a form of septicaemia (infection of the blood) called bacteraemia that can lead to end organ damage and finally death.

The general mechanism of development of pneumonia includes entry of viruses and bacteria from the throat and nasopharynx into the lungs where it attracts alveolar macrophages and neutrophils to initiate immune reactions that destroy the microorganisms. However during such reactions, cytokines (immune system signals) are activated which potentiates macrophages to infiltrate the infected regions and cause further inflammation. These inflammatory cells and the bacteria or virus forms the basis of pneumonia. The release of cytokines is responsible for the fevers, chills and fatigue associated with pneumonia. The quantification and extent of pneumonia is done through radiological examinations and blood tests. The C – reactive protein (cytokine) content in the blood is measured to estimate the severity of infection and probability of development of sepsis.

Pneumonia whether community acquired or hospital acquired is managed by antibiotics of the beta lactam class that includes penicillin and cephalosporin. As a rule of the thumb community acquired pneumonia are treated with first generation cephalosporin as involvement of gram positive organisms are suspected while in case of hospital acquired infections, third generation cephalosporin are used due to involvement of gram negative pathogens.

Atypical pneumonia is a type of pneumonia that is not caused by the traditional pathogens of “typical” pneumonia. The pathogens responsible for atypical pneumonia are Chlamydophila pneumoniae, Mycoplasma pneumonia, Legionella pneumophila, Moraxella catarrhalis, syncitial virus and influenza A virus. Hence the microorganisms involved could be bacteria, fungi, protozoa or viruses. The name was so coined because of its typical clinical features that distinguished it from typical lobar pneumonia. The key symptoms of atypical pneumonia are fever, headache, sweating and myalgia along with bronchopneumonia. Atypical pneumonia is treated with macrolide class of antibiotics like clarithromycin or erythromycin. Penicillin or cephalosporins are effective as because most of these atypical pathogens lack the cell wall where a Penicillin or cephalosporin exerts its antimicrobial actions.

A detailed comparison of pneumonia and atypical pneumonia is presented below:

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