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 healthcare facilities, farms and in the community.

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, with the bacteria following 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 and an introductory video of some of the ways resistant bacteria can 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 may differ, or the abundance of different types may vary. Bacteria can spread from one person to another through direct contact 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 firstline 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. Zoonotic diseases are infections that can spread directly from animals to humans, either directly or by vectors such as ticks and mosquitoes.

Resistant bacteria can be common in livestock, and there are several examples where farmers and their families carry 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.

Food

All animals have bacteria living in and on their bodies. In many animal farms, antibiotics are not only used to treat infections but also to prevent disease events and enhance growth in healthy animals which then selects for resistant bacteria that can spread among the animals. During slaughter or when processing the meat, these bacteria may also be transferred to the product. Crops that come in contact with animal manure may also be contaminated.

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, meat and other products. However, the exact 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.

Measures to reduce the risk of spreading antibiotic resistance via food include the entire food chain, such as disease prevention at the farm and appropriate hygiene from farm to fork. Proper cooking and food handling help decrease the spread of infections as well as resistant bacteria.

Water

Bacteria can spread via drinking water or water supplies used for irrigation, washing cooking utensils, or 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 water; one important source is the release of untreated waste from animals and humans.

Spread within health care facilities

Healthcare facilities are hotspots for the selection and spread of resistant bacterial strains, as many sick people are in close proximity to each other and antibiotic usage is high. Poor hygiene practices can facilitate the spread via the hands or clothes of patients, visitors, doctors, nurses, and other healthcare staff. Other risk factors include improperly cleaned instruments, inadequate cleaning of the facilities, and insufficient sanitation. Crowded wards and a lack of isolation rooms also facilitate the spread. For more on this topic, see Health care-associated infections.

Travel

International travelers spread resistant bacteria across the world. On any given day, several million people catch a flight, and if someone carries a resistant bacterium, they will bring it along. Many studies have shown that a large proportion of international travelers acquire resistant bacteria during visits to areas with a high prevalence of resistant strains (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.

Trade

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