A comparative study of thin-section CT findings between seasonal influenza virus pneumonia and Streptococcus pneumoniae pneumonia

Objective:

To compare the pulmonary thin-section CT findings in patients with seasonal influenza virus pneumonia with Streptococcus pneumoniae pneumonia.

Methods:

The study group included 30 patients (20 males and 10 females; age range, 20–91 years; mean age, 55.9 years) with seasonal influenza virus pneumonia and 71 patients (47 males and 24 females; age range, 27–92 years; mean age, 67.5 years) with S. pneumoniae pneumonia.

Results:

The proportion of community-acquired infection was significantly higher in patients with influenza virus pneumonia than with S. pneumoniae pneumonia (p = 0.001). CT findings of ground-glass attenuation (GGA) (p = 0.012) and crazy-paving appearance (p = 0.03) were significantly more frequent in patients with influenza virus pneumonia than with S. pneumoniae pneumonia. Conversely, consolidation (p < 0.001), mucoid impaction (p < 0.001), centrilobular nodules (p = 0.04) and pleural effusion (p = 0.003) were significantly more frequent in patients with S. pneumoniae pneumonia than in those with influenza virus pneumonia.

Conclusion:

Pulmonary thin-section CT findings, such as consolidation and mucoid impaction may be useful in distinguishing between seasonal influenza virus pneumonia and S. pneumoniae pneumonia.

Advances in knowledge:

(1) Distinguishing seasonal influenza virus pneumonia with S. pneumoniae pneumonia is important. (2) The CT findings of GGA and crazy-paving appearance were more frequently found in patients with influenza virus pneumonia than in patients with S. pneumoniae pneumonia, whereas consolidation, mucoid impaction, centrilobular nodules and pleural effusion were more frequently found in patients with S. pneumoniae pneumonia.Influenza virus is responsible for seasonal epidemics of community-acquired pneumonia (CAP), with outbreaks occurring predominantly during the winter months. Secondary bacterial superinfections are the most frequent complications among fatal cases of seasonal and pandemic influenza.Streptococcus pneumoniae is the most common pathogen of CAP and is also responsible for the increasing frequency of nosocomial pneumonia.^1–3 The mortality related with pneumonia is affected by initial antibiotic therapy; therefore, early detection of S. pneumoniae pneumonia is important for reducing mortality. Moreover, S. pneumoniae has been identified as the most prominent causative agent for secondary bacterial pneumonia following influenza virus infection.⁴A rapid immunochromatographic membrane test was developed for the detection of S. pneumoniae antigens.⁵ It is a useful technique for the rapid diagnosis of S. pneumoniae pneumonia; however, it does have its limitations. For example, urinary antigens of S. pneumoniae pneumonia cannot be detected a few days after S. pneumoniae infection, and assay sensitivity is approximately 70–80%.There are several reports of the radiologic features of novel influenza virus pneumonia and S. pneumoniae pneumonia.^6–8 However, there are few reports of the CT findings of seasonal influenza virus pneumonia.^9–11 Furthermore, to the best of our knowledge, no studies comparing CT findings in patients with seasonal influenza virus pneumonia to those with S. pneumoniae pneumonia have been published. The present study therefore compared the pulmonary thin-section CT findings of patients with seasonal influenza virus pneumonia to those with S. pneumoniae pneumonia.