A secondary infection is an infection that occurs during or after treatment of another pre-existing infection. It may result from the treatment itself or from changes in the immune system.
For example, a vaginal yeast infection that occurs after antibiotic treatment of a bacterial infection is a secondary infection. Bacterial pneumonia after a viral upper respiratory infection is another example.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.