[Role of viral infections in acute exacerbation of idiopathic interstitial pneumonia].

To evaluate the possibility that viral infections can trigger acute exacerbations of idiopathic interstitial pneumonia (IIP), we analyzed data from 105 patients with IIP. Acute exacerbation was defined as an increase in dyspnea, a decrease in PaO2 by more than 10 Torr, and worsening of chest radiographic findings within one month. Viral infection was said to be involved when patients had more than a 4-fold change in viral antibody titer or viral inclusion bodies in sputum during the acute exacerbation. Of the 105 patients with IIP, 30 had acute exacerbations. Among these 30 patients, viral infection was said to be involved in 11 (37%). Presumptive viruses were influenza virus (n = 6), parainfluenza virus (n = 1), herpes simplex virus (n = 1), RS virus (n = 1), and cytomegalovirus (n = 2). The levels of serum immunoglobulin A (IgA) before acute exacerbations were significantly lower (p < 0.05) in patients in whom viral infection was said to be involved. These results suggest that viral infection associated with a low value of serum IgA is an important trigger of acute exacerbations of IIP.