Pathogen Resistance

Antimicrobial resistance occurs when harmful germs evolve to survive the drugs designed to kill them, turning once-treatable infections into serious, sometimes impossible-to-cure health threats that affect millions of people worldwide.

Table of contents

• What Is Pathogen Resistance?
• How Resistance Develops
• Global Impact and Burden
• Main Causes of Resistance
• Who Is Most at Risk?
• How to Prevent Resistance
• Treatment Challenges

What Is Pathogen Resistance?

Antimicrobial resistance (AMR), also known as pathogen resistance, happens when germs like bacteria, viruses, fungi and parasites develop the ability to defeat the medicines designed to kill them^[1][2]. These germs are not killed by the drugs and continue to grow, making infections extremely difficult to treat^[1].

It’s important to understand that your body doesn’t develop resistance—the germs do^[3]. When resistance happens, fewer medicines work against a particular germ. Other drugs often help, but finding effective treatment takes longer and the available options may cause more serious side effects^[3].

Antibiotics are medicines that fight infections caused by bacteria in humans and animals by either killing the bacteria or making it difficult for them to grow and multiply^[1]. Similarly, antifungals treat fungal infections, antivirals treat viral infections, and antiparasitics treat parasitic infections^[2]. Together, these drugs are called antimicrobials.

How Resistance Develops

Resistance is a naturally occurring process. However, the rate at which it develops has been dramatically increased by how antimicrobials are used and misused^[1][2]. Bacteria and other germs follow the same rules of evolution as all organisms, including survival of the fittest. They can evolve much more rapidly than larger organisms because they have simpler genetic structures, shorter generation times, and can exchange genetic material between different species^[9].

Several factors speed up the resistance process. When you take antibiotics, they can kill the bacteria that haven’t changed, but they leave behind resistant bacteria that have developed defenses. These resistant bacteria multiply and become increasingly resistant to medicine^[3].

Sometimes, the genetic makeup of a bacterium changes on its own. The antibiotic doesn’t recognize this newly changed bacterium and can’t target it the way it should^[3]. Bacteria have several main ways to resist antimicrobials: limiting how much of a drug enters their cells, changing the drug’s target, breaking down the drug, or actively pumping the drug out^[4].

You can also pass a drug-resistant infection to someone else. That person now has an infection that won’t respond to certain antibiotics^[3].

Global Impact and Burden

Antimicrobial resistance is one of the world’s most urgent public health problems^[1][2]. The numbers tell a sobering story. Worldwide, bacterial antimicrobial resistance was directly responsible for 1.27 million deaths in 2019 and contributed to nearly 5 million deaths^[2][6].

In the United States alone, more than 2.8 million antimicrobial-resistant infections occur each year. More than 35,000 people die as a result^[1][6]. When Clostridioides difficile—a germ that causes deadly diarrhea and inflammation of the colon and is associated with antibiotic use—is included, the U.S. toll exceeds 3 million infections and 48,000 deaths annually^[1][6].

The economic burden is also substantial. The World Bank estimates that antimicrobial resistance could result in $1 trillion in additional healthcare costs by 2050, and $1 trillion to $3.4 trillion in gross domestic product losses per year by 2030^[2]. In the United States, the estimated national cost to treat infections caused by six antimicrobial-resistant germs frequently found in healthcare can exceed $4.6 billion annually^[6].

Resistance threatens to undo many advances in modern medicine. Medical procedures such as joint replacements, organ transplants, cancer therapy, and treatment of chronic diseases like diabetes, asthma, and rheumatoid arthritis all depend on the ability to fight infections using antibiotics^[1].

Main Causes of Resistance

Several factors contribute to the growing problem of antimicrobial resistance. The most important are related to how these medicines are used.

Overuse of antimicrobials is a major driver. Taking antibiotics when you don’t need them contributes to resistance. For instance, viruses cause most sore throats, and antibiotics won’t help^[3]. More than one out of four antibiotics prescribed in U.S. outpatient settings are unnecessary^[6].

Misuse of antibiotics also accelerates resistance. Bacteria take advantage of any opportunity to multiply. If you forget to take doses, stop treatment too soon, or use someone else’s medicine, bacteria start reproducing and can change as they multiply^[3].

Use in agriculture and animals contributes significantly. Antibiotics used in farm animals and crops can lead to drug-resistant germs that spread to people^[2].

Environmental pollution from pharmaceutical manufacturing and improper disposal of medicines can expose bacteria to low levels of antimicrobials, allowing them to gradually develop resistance^[2].

Self-medication and use of leftover medicines from previous illnesses are also problematic. Different antibiotics work for different bacterial infections, so the choice requires medical training^[3].

Who Is Most at Risk?

Antibiotic-resistant infections can affect anyone. However, certain groups face higher risk due to their health status or living environment^[3].

People more vulnerable to dangerous resistant infections include babies (especially those born early), adults over age 65, people experiencing homelessness or living in crowded conditions, people who have weakened immune systems, and people who take antibiotics long term^[3].

Antimicrobial resistance affects countries at all income levels, but its drivers and consequences are made worse by poverty and inequality. Low- and middle-income countries are most affected^[2].

How to Prevent Resistance

There are many steps that individuals and communities can take to help prevent resistance and protect families.

Practice good hygiene. Keeping your hands clean is one of the best ways to remove germs, avoid getting sick, and prevent spreading germs to others^[17]. Cover coughs and sneezes with a tissue or your elbow^[17].

Get vaccinated. Vaccinations are an important step to prevent infections, including resistant infections. Talk to your healthcare provider about vaccines recommended for all ages^[17].

Use antimicrobials appropriately. Talk with your healthcare provider about the best treatment when you or your family are sick. Antibiotics and antifungals save lives, but any time they are used they can cause side effects and contribute to antimicrobial resistance^[17]. Only take antibiotics when they are prescribed to you by a doctor or certified health professional^[2].

Follow prescription instructions carefully. If your healthcare provider prescribes an antibiotic, take it exactly as prescribed. Don’t stop taking antibiotics if you feel better—you need to take them to kill the germs that are still in your system^[3]. Don’t save remaining antibiotics for later use^[17].

Never share antibiotics or use leftover medications. Old medicines can have lower activity and fail to work^[3].

Prepare food safely. Follow simple steps to avoid foodborne infections—clean, separate, cook, and chill. Wash your hands before and after touching raw meat, chicken, seafood, or eggs^[17].

Practice healthy habits around animals. Always clean your hands after touching, feeding, or caring for animals. Take measures to reduce your contact with animal waste^[17].

Treatment Challenges

As a result of drug resistance, antibiotics and other antimicrobial medicines become ineffective, and infections become difficult or impossible to treat, increasing the risk of disease spread, severe illness, disability and death^[2].

Antimicrobial-resistant infections often require the use of second- and third-line treatments that can harm patients by causing serious side effects, such as organ failure. These infections also prolong care and recovery, sometimes for months^[1]. Infections from resistant germs are more challenging and costly to treat^[3].

In some cases, antimicrobial-resistant infections have no treatment options at all. Today, some strains of bacteria have become resistant to all available antibiotics, while strains of many other serious germs are now resistant to all but one easily administered drug^[9].

The world also faces an antibiotics pipeline crisis. There is an inadequate research and development pipeline in the face of rising levels of resistance. No new antibiotics have been developed in the last 10 years, and bacteria have steadily become more resistant to those that currently exist^[2]. The discovery of truly novel classes of antimicrobial agents has been stalled for decades, with the developmental pipeline relying almost entirely on variations of existing drug types^[9].