Battlefield Theory
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Imagine the scene — from the mouth and nose, through the pharynx into the trachea, separating into the left and right main bronchi at the larynx. This is the start of your airway. This is to be the site of inflammation, or rather, the site of battle. Across the landscape that is the airways, two sides are about to go to war. Invading pathogens versus human inflammatory cells. This war will eventually lead to pneumonia.
To treat pneumonia we need to pin down the exact invading pathogen and treat accordingly. The most common types of infectious agents are viruses and bacteria. But of all the microorganisms that can cause pneumonia, most cases are down to only about two dozen species. Identifying the infecting agent, the actual cause of pneumonia, relies on a lengthy process; from a full patient history and examination, to imaging studies and epidemiological information, together with bacteriological tests.
Despite all of this, in up to 50% cases of pneumonia, the causative pathogen remain unidentified.
In and amongst the invading pathogens are other organisms that are just bystanders — colonizing the airway. Other commensal organisms in and amongst our instigators of war. In diagnosing pneumonia many are implicated and detecting these organisms in the airway does not necessarily mean they are the cause of infection. As such, any commensal organism that falls within a certain spread of criteria is thought to be the causative agent.
The key to all of this is the difference between colonization and infection.
To discriminate between the two types of organisms in a pneumonia infection — infectious and colonizing — researchers from Japan came up with the “pneumonia battlefield“. The titled “Battlefield Hypothesis