, one of the most important Gram-negative bacterial pathogens, is of worldwide concern [14
]. In addition, PA and MRSA are also important causes of nosocomial and community-acquired infection around the world. Initially limited to hospitals, in recent years MRSA has emerged as an increasingly important cause of community-acquired bacterial infection [15
], often affecting healthy children and adults who have no apparent risk factors for infection [18
]. Recently, we have reported that in about 80% of the patients with acute KPP, one or more additional pathogens, predominantly MRSA and PA, were present [10
To the best of our knowledge, no comparisons of clinical and pulmonary CT findings in patients with acute K. pneumoniae
pneumonia alone or combined with other pathogens have been published. We compared retrospectively the clinical and pulmonary thin-section CT findings in 80 patients with acute KPP alone and in 55 patients with concurrent MRSA or 25 with concurrent PA. All patients had several complaints, such as fever and cough. There were no significant differences in presenting symptoms between the three groups. KPP tends to affect people with underlying diseases, such as alcoholism, diabetes and chronic lung disease [19
]. In the present study, alcoholism (60.6%) was the most commonly associated condition, followed by a smoking habit (52.5%), cardiac disease (39.4%) and malignant disease (35.6%). In the patients with concurrent pneumonia (MRSA or PA), underlying conditions such as cardiac diseases, diabetic mellitus and malignancy were significantly more frequent than in patients with KPP alone. As for mortality rate, that in patients with KPP combined with MRSA or PA was significantly higher than that in patients with KPP alone (both p
<0.005). The mortality rate in patients with KPP alone was lower than that in previous studies, and the mortality rate in concurrent KPP was similar to that previously reported [2
]. Therefore, the mortality rates reported previously might reflect that in concurrent KPP.
KPP has been classified by radiographic and clinical criteria [9
]. Carpenter [22
] has divided Klebsiella
pulmonary infections into acute pneumonia and complications of acute pneumonia. The complications consist of lung abscess, pulmonary gangrene and chronic KPP. The frequencies of abscess formation, gangrene and development of chronic pneumonia were 16–50%, 7–50% and 5–33%, respectively [22
In the present study of 160 patients, GGA was most frequent, followed by consolidation and intralobular reticular opacity; however, there was no significant difference between the three groups. CT findings such as centrilobular nodules, bronchial wall thickening and bronchiectasis were significantly more frequent with concurrent pneumonia than those with KPP alone.
Shah et al [25
] have reported CT findings in 28 patients with nosocomial PA pneumonia: 15 with PA and 13 with PA and other pathogens such as Staphylococcus aureus
= 4) and Klebsiella
= 2). The CT findings consisted mainly of consolidation (100%) with bilateral involvement (64.3%), nodules (50.0%), necrosis (35.7%) and centrilobular nodules (32.1%). Bilateral pleural effusion was seen in 13 patients (46.4%). There was no significant difference in the distribution or frequency of abnormal findings between the two groups.
Recently, Nguyen et al [26
] have reported the radiographic and CT findings in nine patients with MRSA pneumonia. The most common CT findings were bilateral consolidation (n
= 8), followed by interlobular septal thickening (n
= 7), cavitation (n
= 6), multiple nodules (n
= 5) and centrilobular nodules (n
= 4). Pleural effusion was present in all patients. Enlarged lymph nodes were present in four patients.
Classified histologically as bronchopneumonia, nodular features would be expected upon CT evaluation of PA pneumonia. Pathologically, bronchopneumonia demonstrates inflammatory changes involving the bronchial and bronchiolar walls, with minimal exudation into adjacent alveoli [27
]. Therefore, in concurrent KPP with PA or MRSA, CT findings of centrilobular nodules, bronchial wall thickening and bronchiectasis might be significantly more frequent than in those with KPP alone.
In the present study, a cavitary lesion was found in only one patient (1.3%) with KPP. The frequency was significantly lower than that in patients with concurrent KPP with PA or MRSA (both, p
<0.001) and compared with previously reported rates [22
]. However, this might be because most of the literature was published from the 1930s to the 1960s, which represents the pre-antibiotic era or a period of minimal antibiotic use. In addition, there have been no studies in which additional pathogens were evaluated in patients with KPP. We have recently reported that in 764 of 962 patients (79.4%) with acute KPP, one or more additional pathogens were found [10
]. In the present study, the frequency of cavitary lesions in concurrent KPP was similar to that in previous studies; therefore, the frequencies reported previously might reflect those in concurrent KPP.
It should be noted that there were several limitations to our study. First, this was a retrospective study and CT image interpretation was performed by consensus. Second, our study lacked a pathological correlation with specific CT findings such as consolidation and intralobular reticular opacity. Third, the thin-section CT images were obtained at several institutions using different protocols. Fourth, CT images in the other concurrent pathogens other than PA and MRSA were not evaluated.
In summary, we investigated the clinical and thin-section CT findings of 80 patients with acute KPP alone, 55 with KPP combined with MRSA and 25 with KPP combined with P. aeruginosa. In the patients with concurrent pneumonia (MRSA or P. aeruginosa), underlying conditions such as cardiac diseases, diabetes mellitus and malignancy were significantly more frequent than in patients with KPP alone. Moreover, CT findings such as centrilobular nodules, bronchial wall thickening, cavity and pleural effusion were significantly more frequent in patients with concurrent pneumonia than those with KPP alone.