Doctors working in hospitals and emergency rooms have seen all kinds of infections and complications — from easily treatable urinary tract infections to potentially deadly sepsis. But some viruses scare them more than others, and they are more common than you think.

Most people probably fear human immunodeficiency virus (HIV), but in reality it’s not something doctors are frightened of, according to Dr. Paul Zelenetz, Chief of Division of Infectious Diseases at ProHEALTH Care. “It’s very rare,” he said. “Between 2000 and 2012, there was only one documented health care-related HIV acquisition.”

A lot of scary infections, such as Ebola, don’t spread that easily, but are made highly contagious because of lack of healthcare, noted Dr. Matthew Sims, director of Infectious Disease Research for Beaumont Hospital, Royal Oak, Michigan. “What makes it scary is where it’s spreading.”

What people in developed countries should be worried about the most are respiratory diseases because they can “really spread like fire,” Sims added. The other worrisome infections are those caused by bacteria that have become resistant due to overuse of antibiotics, according to Bonnie Prokesch, M.D., director of Antimicrobial Stewardship, Parkland Health & Hospital System and Assistant Professor of Infectious Diseases, UT Southwestern Medical Center.

Certain diseases are more likely to spread in hospitals because of the increased risk of accidental sticks with infected needles, and of breathing in an infectious virus or bacteria.

To identify the infections that even doctors find scary, 24/7 Wall St. consulted several doctors specializing in infectious diseases and reviewed prevention and treatment guidelines as well as death toll data from the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO).

Click here to read about 10 infections even doctors are afraid of.