Infections and Sepsis

Overview

An infection is the invasion and growth of germs in the body, such as bacteria, viruses, parasites, and fungi like yeast. An infection can begin anywhere in the body and may spread throughout it.

Your immune system works to stop infections before they take hold. The first immune response when a problem begins is fast and broad. This usually leads to inflammation.

Later, other immune cells (or white blood cells) will activate, divide, and work to fix the problem. Cells called B cells make antibodies that disable germs. Others called T cells kill infected cells and recruit other immune cells.

But sometimes infections still get out of control. Sepsis happens when a person experiences an overwhelming or weakened whole-body immune response to an infection or injury. Sepsis can strike without warning and progress rapidly. Although most infections don’t lead to sepsis, it is a serious condition and a leading cause of death in hospitals.

Related Terms: Sepsis is sometimes called “blood poisoning” or septicemia. Septic shock is a severe complication of sepsis.

Signs and Symptoms

An infection can cause one or more of these signs:

• Fever of 100.4 °F (38 °C) or higher
• Chills
• Cough or sore throat
• Difficulty breathing
• Confusion
• Diarrhea
• Ear pain, headache, sinus pain, or a stiff or sore neck
• Skin rash
• Sores or white coating in the mouth or on the tongue
• Swelling or redness at the location an infection entered through the skin
• Urine that is bloody or cloudy, or pain while urinating

When an infection triggers sepsis, blood pressure drops, the heart weakens, and a person can quickly develop septic shock. Once this happens, multiple organs, such as the lungs, kidneys, and liver, can quickly fail. This multi-organ failure can be fatal.

Even after surviving sepsis, problems can continue. Sepsis can also result in lung injury, muscle wasting, cognitive dysfunction, and reduced blood production. Some people recovering from sepsis have a weakened immune system that leaves them at high risk of future infections.

Related Health Effects

Infections That Spread to the Brain

Meningitis is an infection of the membranes surrounding the brain and spinal cord. It often appears with flu-like symptoms that develop over one to two days. Signs may include:

• Sudden fever
• Severe headache
• Nausea or vomiting
• Double vision
• Sensitivity to bright light
• Stiffness in the neck

Infections That Spread to the Heart

Endocarditis is a rare but life-threatening disease. In endocarditis, clumps of bacteria or fungi from another part of the body get into the bloodstream and collect on the inner lining of the heart, causing inflammation. Pieces of these clumps can also break off and travel to different parts of the body, blocking blood flow or spreading infection.

Symptoms of endocarditis may develop slowly or start suddenly and can range from mild to severe. Common symptoms include:

• Fever
• Heart murmur or abnormal heart sounds
• Fatigue
• Chest pain
• Cough, with or without blood
• Stomach pain
• Shortness of breath
• Night sweats
• Loss of appetite and weight loss
• Muscle, joint, and back pain
• Skin changes, such as tiny reddish-purple spots from broken blood vessels

Infections in People with Weakened Immune Systems

Opportunistic infections are infections that happen more often or are more severe in people with weakened immune systems. People with weakened immune systems include people with human immunodeficiency virus (HIV) or cancer, those who receive organ transplants, and people on medicines that weaken their immune systems. An impaired immune system makes it harder for the body to fight off opportunistic infections, which take advantage of a person’s weakened immune defenses.

Causes and Risk Factors

The germs that cause infections can spread in many ways, including through the air, body fluids, contaminated food or water, and contaminated surfaces.

Because white blood cells are so important for fighting bacterial and fungal infections, infections are more likely to occur when someone has fewer of these cells. Neutropenia is a condition where white blood cells decrease to a dangerous level. Cancer and medical treatments such as chemotherapy can cause neutropenia, as can certain chronic diseases like HIV and lupus.

There are also many other factors that increase risk for infection, including:

• Taking medicines that weaken the immune system, such as corticosteroids
• Stress
• Poor nutrition
• Not enough sleep
• Not receiving recommended vaccinations for infectious diseases

When an infection triggers sepsis, the dangerous effects happen because the body releases substances into the blood to fight the infection. If unchecked, these substances trigger widespread inflammation, blood clots, and leaky blood vessels. As a result, blood flow slows, limiting nutrients and oxygen in organs. This can lead to organ damage.

Bacterial infections cause most cases of sepsis. However, viral infections like COVID-19 or the flu, fungal infections, parasites, and non-infectious problems like traumatic injuries can also cause sepsis. Sometimes, doctors can’t figure out the cause, especially when bacteria are involved and a person has already used antibiotics. This is because these medicines kill the bacteria and make them no longer detectable.

The people at highest risk of sepsis are:

• Infants and children
• Older adults
• People with underlying medical problems
• People with weakened immune systems
• People with other injuries or who recently had surgery
• People taking certain medicines that weaken the immune system

Prevention Guidance

Your healthcare team may recommend these steps to prevent infection:

• Wash your hands often with soap and warm water, especially before eating
• Keep cuts and scrapes clean
• Stay away from people who are sick
• Avoid crowds and people who have recently had a live vaccine
• Follow food safety guidelines — make sure meat, fish, and eggs are well cooked, and keep hot foods hot and cold foods cold
• Make sure you are up to date on vaccines

Prepare for medical visits by making a list of questions to ask your healthcare team, including:

• Am I at increased risk of infection during treatment? When am I at increased risk?
• What steps should I take to prevent infection?
• What signs of infection should I look for?
• Which signs signal that I need urgent medical care at the emergency room? Which should I call you about?

Vaccines

Vaccination teaches your immune system to fight a specific germ without you having to get sick first. This immune system training can decrease the likelihood that you get infected with that germ. A vaccine can also reduce the severity of the infection if it occurs.

Diagnosing Infections

Doctors can use tests called blood cultures, which may be able to identify the exact bacteria, virus, or fungus causing an infection. They can also use other blood tests to check for the amounts of different types of white blood cells, since a low count can raise the risk of infection.

Treatment and Management

Treating Infections

Call your healthcare team if you have signs of an infection. This is especially important for people with cancer, since infections during cancer treatment can be life-threatening and require urgent medical attention. People with weakened immune systems due to other conditions or certain medicines also need to pay special attention to signs of an infection.

Talk with your doctor or nurse before taking medicines for a fever, including aspirin, acetaminophen, or ibuprofen. These medicines can lower a fever but may also mask signs of a more serious problem.

There are many medicines to treat infections, including antiviral, antibiotic, antifungal, and antiparasitic drugs. The type of medicine used depends on the type of germ that caused the infection.

Treating Sepsis

Unfortunately, there is no specific treatment for sepsis. Instead, treatment includes supportive care for the health problems resulting from sepsis and therapy to fight germs that may be the underlying cause. Antibiotics are used if an infection is suspected or found.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on infections and sepsis.

Community Support

• Centers for Disease Control and Prevention (CDC)
• Meningitis Foundation of America, Inc.

Note: This resource list is for informational purposes only. It is not comprehensive, and an organization’s inclusion does not constitute an endorsement by NIH.  

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

Researchers funded by NIH are currently exploring ways to better treat different types of infections and improve survival. They are also developing genetic tools to determine how some infection-causing germs are able to survive exposure to treatments designed to kill them. In addition, NIH-funded scientists are working to create new vaccines to protect people from a wide variety of infectious diseases, including HIV.

To improve treatments for sepsis, NIH-funded scientists are searching for faster and more accurate tests to diagnose and classify sepsis during its early stages. This includes exploring the activity of proteins and other biological chemicals in the blood. These markers can give healthcare providers information on how severe a case of sepsis is and whether it might progress. For example, NIH funded the creation of the first FDA-approved AI-based sepsis diagnosis algorithm, the Sepsis ImmunoScore.

NIH-funded scientists have also created artificial replicas of human organs, such as organoids or organ-on-chips, using human cells to test potential drugs as sepsis treatments.

NIH researchers are working to answer other key questions about sepsis, including:

• What patient traits are associated with sepsis? Researchers are looking for molecular markers associated with overall sepsis risk and poor long-term outcomes.
• How does the body fight sepsis? Researchers are studying the mechanisms of immune resolution to investigate new therapies that may be useful for controlling sepsis.
• How do healthcare inequities contribute to sepsis outcomes? African American/Black and Latino people experience a lower quality of care and higher rates of complications and death from sepsis when compared to non-Hispanic White people. NIH researchers are developing interventions to address these issues.
• What causes poor health outcomes in some sepsis survivors? Researchers are studying why some people recovering from sepsis have a weakened immune system and whether the nervous system has a role in this.

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.