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Difference between Viral and Bacterial Pneumonia


The names of these two different main strains of pneumonia really say it all. Viral pneumonia is contracted from a virus, while bacterial pneumonia is caused by bacteria. The main distinctions between the two causal elements are that virus cells are smaller than the single-celled micro-organisms that make up bacteria, and most bacteria (unlike viruses) are not harmful to humans.

Root Causes

In both cases, the bacteria and viruses invade the lungs and cause an inflammation. The bacteria most responsible for cases outside of hospital environments is known as “streptococcus penumoniae.” However, patients often contract the bacterial form of the disease from not just one but multiple strands of bacteria at the same time. Other bacteria that can cause pneumonia include straphylococcus aureus, haemophilus influenza, and klebsiella pneumoniae.

Viral pneumonia is generally not nearly as serious. It is often caused by the same sorts of viruses that trigger common colds and the flu. The most serious strand is the one caused by influenza viruses, and was especially bad before the advent of modern medicine. In some cases, viral pneumonia breaks down the body’s resistance, creating what’s known as a “prime environment” for the secondary arrival of bacterial pneumonia. Indeed, studies of the great influenza epidemic of 1918-18 have concluded that the majority of deaths were a result of bacterial co-infection.


Clinicians also like to divide cases of pneumonia based on the environment where the disease is contracted. In the case of more serious bacterial pneumonia, this breaks down as follows: community-acquired (outpatient setting, within 48 hours of hospital admission); hospital and institutional-acquired; ventilator-associated; aspiration caused; and nosocomial pneumonia, a more critical sub-set of hospital-acquired forms of the disease.

Viral pneumonia is most prevalent among cases of child affliction, in keeping with the vulnerability of younger populations and the high levels of sick-to-healthy child contact. Viruses have been found to be responsible for up to half of studied child pneumonia victim groups.



Mayo Clinic – What’s the Difference Between a Bacterial Infection and a Viral Infection?, Retrieved June 12, 2011 from

Mayo Clinic – Pneumonia, Retrieved June 12, 2011 from

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