No one has immunity against AMR, but certain populations of people and certain drugs are at higher risk for resistance. "Any antibiotic that is constantly overprescribed and unnecessary is at risk for resistance," Goff said, adding, "The more you use an antibiotic, the less effective it becomes." For example, erythromycin is a short-course antibiotic that's been widely used since the 1950s. It's prescribed to treat a number of infections caused by bacteria, including respiratory infections, pneumonia, ear infections, urinary tract infections and sexually transmitted diseases (STDs). Over the years, the bacteria group A Streptococcus has become resistant to the drug, making erythromycin useless against many of these infections. According to Mateo-Contreras, individuals who are hospitalized or living in long-term care facilities such as nursing homes tend to use antibiotics more than other people, and have a higher risk of developing antibiotic resistance. He adds that individuals with chronic conditions that affect the immune system, such as cancer, have added vulnerability to resistance as well.