Klebsiella pneumoniae is a gram negative organism that usually affects people with alcoholism or chronic debilitating diseases (similar to other gram -ve pneumonias). On CXR, consolidation is lobar and resembles streptococcus pneumonia. Lobar expansion (e.g. bulging of the horizontal fissure in this case) is less common nowadays with modern antibiotic treatment. Also, lobar expansion is not specific for Klebsiella infection.

A helpful feature which may help to distinguish from pneumococcal pneumonia is that Klebsiella pneumonia develops cavitation in 30-50% of cases. This occurs early and progresses quickly. Massive necrosis (pulmonary gangrene) is a recognized complication. In comparison, cavitation is rare in pneumococcal pneumonia.