Viral Pneumonia Requiring Differentiation from Acute and Progressive Diffuse Interstitial Lung Diseases

Ishiguro, Takashi; Kobayashi, Yasuhito; Uozumi, Ryuji; Takata, Naomi; Takaku, Yotaro; Kagiyama, Naho; Kanauchi, Tetsu; Shimizu, Yoshihiko; Takayanagi, Noboru

Several symptoms and laboratory findings have been reported as suggestive of pure viral pneumonia as opposed to bacterial pneumonia: less productive cough, lower peripheral white blood cell counts, lower procalcitonin and CRP levels, and higher serum creatine kinase values (9, 10). Our study compared viral pneumonia and other acute diseases and found that sore throat and fever were observed significantly more frequently in patients with viral pneumonia than in those with other diseases. Laboratory tests showed higher liver transaminase and CRP values, and lower numbers of eosinophils in the BALF of patients with viral pneumonia than in those with other diseases. Our study also showed that it was difficult to distinguish viral pneumonia from acute ILDs or pneumonia due to unknown etiology using procalcitonin alone, although procalcitonin is used as a marker for discriminating between viral and bacterial infections (11) . Conventional diagnostic tests for respiratory viral infection include culture, serology, and direct fluorescence antibody staining; however, these methods are limited by slow turnaround time or insufficient sensitivity. Although PCR techniques are more labor intensive and technically demanding and require specialized laboratory equipment, they have high sensitivity, and our study suggested their usefulness in the detection of viral infection. Nasopharyngeal RDTs in 10 patients with primary influenza viral pneumonia were all negative in our study, which was supported by the low sensitivity of nasopharyngeal RDTs in the 2009 pandemic (12) . We did not perform RDTs using BALF; however, PCR tests using BALF were useful and are recommended for the diagnosis of primary influenza viral pneumonia. Some of our study patients had positive PCR results that were considered to indicate colonization. In previous adult studies, viruses were detected in 0.4-4.2% of asymptomatic patients (13) (14) (15) (16) . Differentiating infection and colonization is still difficult using PCR methods; thus, physicians should not diagnose patients as having a viral infection based on PCR results alone.