Sepsis is caused by an infection that triggers an extreme, harmful response from the body’s immune system. Bacteria cause most cases, but viruses and fungi can also lead to sepsis, and some infections begin in the lungs, urinary tract, abdomen, skin, or a wound. As the body reacts, inflammation can damage tissues and organs. Sepsis can develop from an infection that seemed minor or was not yet recognized.
How Does an Infection Lead to Sepsis?
Sepsis develops when the body's response to an infection becomes uncontrolled or harmful. Normally, the immune system works to fight germs and contain an infection. During sepsis, the response can disrupt normal body functions and damage the body's own tissues and organs. This damage can affect vital organs, including the kidneys, lungs, heart, and brain.
According to the World Health Organization (WHO), sepsis involves organ dysfunction caused by an abnormal response to infection. It is not simply another name for having an infection. An infection may remain in one area, such as the lungs or urinary tract, while the body's harmful response affects functions throughout the body.
Not everyone who develops an infection will develop sepsis. The progression depends on several factors, including the infection involved, the person's health, and how their body responds. Sepsis can also develop before someone knows that an infection is present, which means its original cause may not be obvious at first.
Which Infections Can Cause Sepsis?
Almost any infection can lead to sepsis, although some types are more commonly involved. Bacterial infections cause most cases. Viral and fungal infections can also trigger sepsis, and the WHO recognizes parasitic infections as another possible cause. The Centers for Disease Control and Prevention (CDC) explains that an infection caused by different types of germs can trigger the chain reaction that leads to sepsis.
The germ responsible for an infection is not always known when sepsis first develops. Healthcare professionals may need to investigate the source of the infection and identify the organism involved to help guide treatment. The fact that a particular infection can cause sepsis does not mean that every person who develops that infection will experience this complication.
Where Do Infections That Lead to Sepsis Usually Begin?
Infections that lead to sepsis often begin in a specific part of the body. The Mayo Clinic identifies several common sources, including the lungs, urinary system, digestive system, bloodstream, wounds, burns, and catheter sites.
- Lungs: Pneumonia and other lung infections can sometimes progress to sepsis.
- Urinary tract: Infections involving the bladder or kidneys may lead to sepsis.
- Abdomen and digestive system: Infections inside the abdomen, including those associated with conditions such as appendicitis, can be a source.
- Skin and soft tissues: Cellulitis, infected cuts, burns, and other wounds may provide an entry point for germs.
- Bloodstream: Infections involving the blood can be associated with sepsis, although sepsis is defined by the body's harmful response to infection rather than simply by the presence of germs in the blood.
- Medical devices and surgical sites: Infections associated with intravenous lines, urinary catheters, surgical wounds, or other medical procedures can sometimes lead to sepsis.
These examples cover common infection sources, but they are not the only possibilities. An infection in another part of the body can also trigger sepsis. Sometimes, the original source is difficult to identify, particularly when the person has few obvious signs of the infection that started the process.
Why Do Some People Develop Sepsis After an Infection?
Having an infection does not automatically lead to sepsis. The body's response, the person's general health, and other medical circumstances can influence the risk. Some people have a greater chance of developing sepsis or experiencing complications when an infection occurs.
According to MedlinePlus, groups with a higher risk include older adults, young children, pregnant people, and people with certain long-term health conditions or weakened immune systems.
- Very young children and older adults: Infants and older people are more vulnerable to complications from infections. Signs may also be less obvious in some individuals.
- People with weakened immune systems: Conditions such as cancer, as well as certain treatments that suppress immune function, can increase vulnerability to infections.
- People with chronic medical conditions: Diabetes, kidney disease, lung disease, and other long-term illnesses can be associated with a higher risk.
- People who are pregnant or recently gave birth: Infections associated with pregnancy or the period after childbirth can sometimes progress to sepsis.
- People who are hospitalized or recovering from a procedure: Medical conditions, wounds, and infections linked to healthcare can contribute to the risk.
- People with serious wounds or burns: Damaged skin can make it easier for germs to enter the body and cause infection.
These factors increase risk but do not determine whether sepsis will occur. A person without any known risk factors can still develop it, while someone with several risk factors may experience an infection without developing sepsis.
Can Sepsis Develop After Surgery or a Hospital Stay?
Yes. Sepsis can develop from an infection that occurs during or after medical care. Possible sources include an infected surgical wound, an intravenous line, a urinary catheter, or another healthcare-associated infection. People receiving intensive medical care may also be vulnerable because of their underlying illness or the procedures needed to treat it.
Healthcare-associated infections can involve germs that are resistant to some antimicrobial medicines, making the infection harder to treat. The World Health Organization identifies antimicrobial resistance as an important concern in healthcare-associated sepsis. These infections do not mean that a medical procedure necessarily caused harm; they are possible complications that healthcare teams work to prevent and identify promptly.
Can Sepsis Happen Without an Obvious Infection?
Yes. Sometimes, a person does not realize that an infection is present when sepsis begins. An infection may have subtle symptoms, or changes in the person's condition may develop before the original source is clear. In other cases, there may already be symptoms associated with an infection, such as a cough, pain when urinating, or a wound that is not healing as expected.
It is not always possible to predict which infection will progress to sepsis. Healthcare professionals consider the person's symptoms, medical history, examination findings, and changes over time. They may also use blood tests, cultures, or imaging to look for infection and signs of organ dysfunction. The results help them assess the situation and investigate the source.
What Can Help Reduce the Risk of Sepsis?
Because sepsis begins with an infection, preventing infections and getting appropriate care when one develops are important ways to reduce risk. The CDC recommends measures such as practicing good hygiene, preventing infections, keeping wounds clean and covered, receiving recommended vaccinations, and acting quickly when signs of sepsis appear.
Taking prescribed medicines as directed, managing long-term medical conditions, and following wound-care instructions can also support infection prevention. Antibiotics should be taken only as prescribed; they treat certain bacterial infections but do not treat viral infections. Do not use leftover antibiotics or change a prescribed treatment without appropriate medical guidance.
In healthcare settings, infection-prevention practices include hand hygiene, proper care of medical devices, and attention to surgical wounds. Healthcare professionals can advise on specific precautions based on a person's health, medical procedures, and risk of infection.
When Should You Seek Emergency Medical Care?
Sepsis is a medical emergency, and prompt treatment is important. Seek emergency medical care if an infection is accompanied by concerning changes such as confusion, difficulty breathing, unusually rapid breathing, extreme discomfort, clammy skin, or a rapid decline in the person's condition. A person may not have every possible symptom, and fever is not always present.
Babies, young children, and older adults may show different or less obvious signs. In a baby or child, unusual difficulty waking, poor feeding, breathing problems, or a marked change in responsiveness can require urgent assessment. The NHS advises getting immediate medical help when sepsis is suspected. Do not wait for every symptom to appear or for the source of an infection to become clear before seeking help.