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Understand  –  Antibiotic resistance

Spread of resistant bacteria

Resistant bacteria spread via many routes. Different factors influence spread depending on the setting. Poor hygiene, poor sanitation, and poor infection control are three interconnected key factors contributing to the spread of resistant bacteria in health care facilities, in the community as well as in animal production.

Bacteria know no boundaries and international traveling and trade help disseminate resistant bacteria across the world. Animals for food production are transported across borders and groceries are exported from most parts of the world, and the bacteria follow along. This contributes to the complexity of the antibiotic resistance problem and underpins the fact that it is a global issue. It does not matter where a resistant bacterium forms. If it is successful and increases in numbers it may quickly spread to other parts of the world in our globalized society.

Here follows an overview including an introductory video and short descriptions of some of the ways resistant bacteria can spread in society, health care facilities and around the world, as well as a discussion of the factors influencing spread. For more information, see the selected resources at the bottom of the page, or read more in How did we end up here?

Person to person

Bacteria are everywhere, and we are exposed to them all the time. We all have our own unique bacterial “makeup”; some types of bacteria may be the same across populations while others differ, or the abundance of different types may vary. Bacteria can spread from one person to another through direct contacts between people. Transmission can also occur indirectly, for example when someone coughs. If a person contaminates a surface (such as a doorknob) with bacteria, these bacteria can be transferred to another person who touches the surface. That does not necessarily mean that this person will be infected or colonized by these bacteria. Good hand hygiene is important to limit the spread of pathogens and the risk of becoming a carrier of resistant bacteria. Still, even with good hygiene practices, bacteria are a normal part of our surroundings that we will be continuously exposed to.

Animals to humans and vice versa

Bacteria can spread from animals to humans, but also the other way around; from humans to animals. When animal pathogens become resistant to first line antibiotics, diseases become more difficult to treat, just as in humans. Many people come in close contact with animals in their daily life as we keep them as pets in our homes or raise animals for food. Wildlife encounters are also possible. Resistant bacteria can be common in livestock and there are several examples of how farmers and their families have become colonized with the same resistant bacteria as their animals (for example). Likewise, livestock veterinarians are at risk of carrying livestock-associated resistant bacteria. The bacteria may then spread further in society. Zoonotic diseases are infections that can be passed from animals to humans, either directly or by vectors such as ticks and mosquitoes.


All animals have bacteria living in and on their bodies. In many animal farms, antibiotics are used to prevent and treat infections as well as for growth promotion, and the animals may become colonized with antibiotic resistant bacteria. During slaughter or when processing the meat, these bacteria can potentially be transferred to the product. Furthermore, fruits and vegetables can become contaminated with animal feces directly from the animals or via water contaminated with human or animal waste that is used for irrigation of the crops. Eating food contaminated with bacteria may directly cause an infection, such as diarrhea caused by salmonella, campylobacter and enterohaemorrhagic E. coli (EHEC). Resistant bacterial strains, or genes encoding resistance, may also be transferred to the normal gut flora of the consumer without causing an infection. The resistant bacteria can potentially cause infections later on and spread to other people.

Resistant bacteria are frequently detected in chicken and meat. However, the impact of this is for human health is currently not known and may differ in different parts of the world. Some studies demonstrate similarities between the antibiotic resistance genes found in meat and those found in human pathogens, while other studies have not seen this connection, see for example. More research is needed to determine the scale of the problem. Proper cooking and handling of food helps to decrease the spread of infections as well as resistant bacteria.


Bacteria can spread via drinking water or water supplies that are used for example for irrigation, washing cooking utensils or for hygienic purposes. Resistant bacteria have been found in many water sources such as drinking wells, rivers and effluents from wastewater treatment plants. Several bacterial diseases can spread via contaminated water, including typhoid fever and cholera. There are many ways resistant bacteria can end up in the water; release of untreated waste from animals and humans is one important source.

Spread within health care facilities

Health care facilities are hot spots for resistant bacteria since many sick people are in close vicinity of each other and antibiotic usage is high resulting in selection and spread of resistant strains. Poor hygiene practices may facilitate the spread of resistant bacteria via the hands or clothes of doctors, nurses and other health care staff, patients or visitors. Other risk factors include instruments that are not cleaned properly, improper cleaning of the facilities and insufficient sanitation. Crowded wards and few isolation rooms further facilitate spread. For more on this topic, see Health care-associated infections.


International travelers spread resistant bacteria across the world. Any given day several million people will catch a flight, and if someone carries a resistant bacterium they will bring it along. Many studies have demonstrated that a large proportion of international travelers acquire resistant bacteria during visits in areas with a high prevalence of resistant bacteria (reviewed in). The risk is even higher for hospitalized patients, who are exposed to additional risk factors. Several hospital outbreaks have originated from patients transferred from another hospital with high prevalence of resistance.


Meat, fruits, vegetables, seeds, grain, and animals… the list of goods that are being imported and exported to and from different countries all over the world can be made long. Bacteria can potentially spread with any.

Selected Resources

Resource Description
How resistance happens and spread (PDF) Infographic about how resistance develops and examples of how resistant bacteria spread.
MRSA – The evolution of a drug-resistant superbug Short video slideshow describing the evolution of a new variant of MRSA (methicillin-resistant S. aureus) and how it has spread between humans and animals (2 min).
Drugs make bugs Short video describing how and why antibiotic resistant superbugs arise in animal farms where antibiotic usage is high and how they can spread in the environment (3 min).
How does antibiotic resistance spread? Infographic about the spread of antibiotic resistance, developed by the European Centre for Disease Prevention and Control (ECDC), available in all EU/EEA official languages.