Serum adenosine deaminase in viral and bacterial pneumonia.

We measured the activity of serum adenosine deaminase (ADA) in paired sera from 171 military conscripts with radiographically verified pneumonia. Patient serum samples were selected on the basis of serologic analyses identifying as single etiologic agents Streptococcus pneumoniae in 29 patients, Haemophilus influenzae in 7, Mycoplasma pneumoniae in 43, adenovirus in 24, influenza A or B in 12, and parainfluenza in 5 patients. In 14 patients Neisseria meningitidis and in 31 Chlamydia spp were considered the main etiologic agent. Compared with a control group of 45 healthy men, the ADA activity in patients with pneumonia was significantly higher (p less than 0.001) in all patient groups except those with meningococcal pneumonia. The highest ADA levels were seen in patients with pneumonia caused by M pneumoniae (27.4 +/- 9.7 U/L), Chlamydia spp (26.3 +/- 9.1 U/L), and adenovirus (28.5 +/- 10.9 U/L) compared with the controls (11.1 +/- 3.0 U/L). In patients with meningococcal pneumonia, the ADA activity was significantly decreased (p less than 0.001). Serum ADA activity probably reflects differences in cellular immune response to different infectious agents. The ADA determinations may give corroborative information on the etiologic agent of pneumonia.