Not all journal articles are peer reviewed because not all journals are peer reviewed.
Articles in peer-reviewed journals are reviewed by a group of the writer's peers (other expert academics in their field) before the articles are published.
You can find out if a journal (and its articles) is peer reviewed by searching for the journal title in Ulrich's.
How do you know if an article is from a peer-reviewed journal? Some databases allow you to limit your search to peer-reviewed journals. For other databases, you need to look up the title of the journal in Ulrich's Directory.
1. Go to Ulrich's.
2. Type the JOURNAL TITLE (not the article title) into the search box, and click the green search button.
3. In the search results, look for a referee jersey icon to indicate that a journal is refereed. Refereed means the same as peer reviewed.
4. In this case, the Journal of Infectious Diseases IS peer reviewed.
REMEMBER: You are looking for the JOURNAL TITLE in your search results, NOT the article title.