Most common pathogens are Pneumocystis jiroveci, Mycobacterium avium-intracellulare complex, Streptococcus pneumoniae, Haemophilus species. Less frequent pathogens are Cryptococcus neoformans, Histoplasma capsulatum, Coccidioides immitis, cytomegalovirus (CMV), and Toxoplasma gondii. Chemotherapy-induced immunodeficiency may lead to severe lung infections. Pathogens commonly associated with lung infectioins are bacteria (like Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Nocardia species), viruses (eg, respiratory syncytial virus, parainfluenza virus, influenza virus A and influenza B, and cytomegalovirus), and fungi (eg, Aspergillus, Fusarium, and Mucorales species, and Pneumocystis jirovecii). Double pneumonia (bilateral pneumonia)
This is a historical term for acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). However, the term was and, especially by lay people, still is used to denote pneumonia affecting both lungs. Accordingly, the term double pneumonia is more likely to be used to describe bilateral pneumonia than it is ALI or ARDS. Severe acute respiratory syndrome
Severe acute respiratory syndrome (SARS) is a highly contagious and deadly type of pneumonia which first occurred in Nov-2002 after initial outbreaks in China caused by SARS-CoV/SARS-CoV-1,which almost disappeared by the month of May-2004. The second outbreak of SARS-CoV-2 started in December 2019 from Wuhan, China and was declared pandemic by WHO on 11 March 2020. SARS is caused by the SARS coronavirus, a previously unknown pathogen. By area of lung affected
Initial descriptions of pneumonia focused on the anatomic or pathologic appearance of the lung, either by direct inspection at autopsy or by its appearance under a microscope. A lobar pneumonia is an infection that only involves a single lobe, or section, of a lung.
Lobar pneumonia is often due to Streptococcus pneumoniae (though Klebsiella pneumoniae is also possible.) Multilobar pneumonia involves more than one lobe, and it often causes a more severe illness. Bronchial pneumonia affects the lungs in patches around the tubes (bronchi or bronchioles). Interstitial pneumonia involves the areas in between the alveoli, and it may be called "interstitial pneumonitis." It is more likely to be caused by viruses or by atypical bacteria.The discovery of x-rays made it possible to determine the anatomic type of pneumonia without direct examination of the lungs at autopsy and led to the development of a radiological classification. Early investigators distinguished between typical lobar pneumonia and atypical (e.g. Chlamydophila) or viral pneumonia using the location, distribution, and appearance of the opacities they saw on chest x-rays. Certain x-ray findings can be used to help predict the course of illness, although it is not possible to clearly determine the microbiologic cause of a pneumonia with x-rays alone. With the advent of modern microbiology, classification based upon the causative microorganism became possible. Determining which microorganism is causing an individuals pneumonia is an important step in deciding treatment type and length. Sputum cultures, blood cultures, tests on respiratory secretions, and specific blood tests are used to determine the microbiologic classification. Because such laboratory testing typically takes several days, microbiologic classification is usually not possible at the time of initial diagnosis. Clinical
Traditionally, clinicians have classified pneumonia by clinical characteristics, dividing them into "acute" (less than three weeks duration) and "chronic" pneumonias.