Immunity and infection prevention

What is sepsis?

Sepsis is not a separate germ: it is the body’s overwhelming response to an infection, a response that damages its own organs. Sepsis can develop within hours and needs urgent treatment. People with leukemia, especially during neutropenia, are at higher risk. This topic explains what sepsis is, how to recognise it, how it is treated in hospital and how recovery goes afterwards.

Last updated: 3 October 2026~7 min read

Warm red-orange waves of light spreading from a single point through a translucent human silhouette on a dark navy background. — **Figure 1.**Concept: in sepsis, the immune reaction spreads from one site to the whole body.

01Short answer

Sepsis is a life-threatening condition in which a disordered, excessive immune response to infection disrupts how the organs work. Any infection can lead to sepsis, but bacterial infections of the lungs, urinary tract, gut and skin are the most common causes. Signs include confusion, very fast breathing, a racing pulse, pale, bluish or mottled skin, severe shivering, a very high or very low temperature and passing little urine. A fever or signs of sepsis during neutropenia are an emergency known as “neutropenic sepsis”. Treatment happens in hospital: intravenous antibiotics are started as soon as possible, ideally within one hour, along with fluids, oxygen and, if needed, intensive care support. Timely treatment saves lives.

02Simple explanation

Normally the immune system fights an infection where it is, for example in the bladder or in part of a lung. In sepsis, this fight gets out of control and spreads through the whole body. Blood vessels widen and start to leak, blood pressure falls, and the organs do not get enough oxygen.

Any infection can turn into sepsis. According to the CDC, the infections that lead to sepsis most often start in the gut, lungs, skin and urinary tract. Bacteria are the main cause, but viruses such as flu, and fungi, can also cause sepsis.

In leukemia and after chemotherapy, when neutrophils are low, an infection can spread very quickly. Sepsis that develops during neutropenia is called neutropenic sepsis. At such times signs may be faint, and the temperature may be low rather than high.

Signs of sepsis include confusion or slurred speech, uncontrollable shivering, muscle pain, difficulty breathing, pale, grey, bluish or blotchy skin, a very high or very low temperature, and passing very little urine all day. Not every sign has to be present.

The most important thing is time. When sepsis is recognised early and treated quickly, most people recover. So if you feel that “something is seriously wrong”, trust your instincts and get help straight away.

03Scientific explanation

Definition. Under the international Sepsis-3 consensus of 2016, sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection. Organ dysfunction is measured as a rise of at least 2 points on the SOFA score. Septic shock is a severe form of sepsis: despite adequate fluids, medicines that tighten blood vessels are needed to keep the mean arterial pressure at 65 mmHg, and lactate stays above 2 mmol/L; hospital mortality in this case is over 40%.

How common is it? According to the Global Burden of Disease analysis published in the Lancet in 2020, there were about 48.9 million cases of sepsis and 11 million sepsis-related deaths worldwide in 2017, around 20% of all deaths. WHO notes that sepsis is especially dangerous for older people, very young children, pregnant women and people with serious long-term illnesses. According to the CDC, most cases of sepsis start before the person reaches hospital.

Treatment principles. Under the international Surviving Sepsis Campaign 2021 guidelines, antimicrobial treatment should start within one hour for possible septic shock or a high likelihood of sepsis; when circulation is failing, intravenous crystalloid fluids are given in the first hours, norepinephrine is the first-choice vessel-tightening medicine, and the source of infection is removed as soon as possible (for example, an infected catheter is taken out). In a 2006 study of patients with septic shock, each hour of delay in effective antibiotics after blood pressure fell was linked to an average 7.6% drop in survival over the first 6 hours.

Risk assessment and recovery. In the UK, the new NICE NG253 guideline recommends assessing sepsis risk in people over 16 in hospitals and ambulances with the NEWS2 score (breathing rate, oxygen, blood pressure, pulse, alertness and temperature); neutropenic sepsis has its own guideline, CG151. Sepsis survivors have a higher risk in the following months of new physical, psychological and cognitive problems, repeat infections and readmission to hospital; a review in JAMA recommends early referral for rehabilitation and a review of medicines.

04What happens in the body?

When should you seek urgent help?

Call emergency services or your hematology team’s 24-hour number straight away if: breathing is very fast or difficult; there is confusion, slurred speech or unusual sleepiness; the skin, lips or tongue are pale, grey, bluish or blotchy; the temperature is above 38 °C or below 36 °C, or there is severe shivering; you have passed very little urine all day; or you feel that “something is seriously wrong”. Do not drive yourself.

How is sepsis different from an ordinary infection?

In an ordinary infection, inflammation stays in one place, for example the throat or the skin. In sepsis, the immune response spreads through the whole body and damages organs far from the infection, such as the kidneys, lungs, brain and heart. Sepsis is sometimes called “blood poisoning”, but it can develop even without germs in the blood.

A small calm spark on the left and a wide, bright red web of light spreading out on the right, against a dark background. — **Figure 2.**In an ordinary infection, inflammation stays in one place; in sepsis, it affects the whole body.

What is special about neutropenic sepsis

When neutrophils are low, an infection can become serious within hours, while the usual signs are faint. So in the weeks after chemotherapy, any fever or sudden feeling of being unwell is treated as possible sepsis. At the emergency department, say straight away that you are having leukemia treatment and give the date of your last course.

What happens in hospital?

Blood tests are taken, including blood cultures and lactate, an intravenous antibiotic is started without delay, and fluids and, if needed, oxygen are given. If blood pressure falls, medicines that tighten blood vessels may be needed in intensive care, sometimes with a breathing machine or kidney support. Doctors look for the source of the infection and remove it where possible.

Waves of light slowly turning calm teal and gold on a dark navy background, with a smooth even line like a steady pulse in the foreground. — **Figure 3.**After timely treatment, the body gradually calms down and recovery begins.

Recovering after sepsis

Recovery can take weeks, sometimes months. According to the NHS, some people develop “post-sepsis syndrome” afterwards, with tiredness, problems with sleep and memory, muscle weakness, anxiety or depression; it often lasts 6 to 18 months. Gradual physical activity, enough sleep, a balanced diet and sharing your feelings all help. Seek help quickly if new signs of infection appear.

Questions you can ask your doctor

When is my risk of sepsis highest? Which signs mean I should call an ambulance straight away? What should I say at the emergency department, and which documents should I take? If I have had sepsis, how will my leukemia treatment change? What rehabilitation or psychological support can I get during recovery?

05From infection to sepsis

Simplified: how sepsis develops and when acting matters most.

1InfectionLungs, urinary tract, gut, skin or a catheter.

2OverreactionThe immune response spreads through the whole body.

3Organs affectedBlood pressure falls and organs get too little oxygen.

4Urgent treatmentAntibiotics, fluids, oxygen, intensive care support.

The first hourAntibiotics as soon as possible.

Organ supportIn intensive care if needed.

RecoveryOver weeks and months, with support.

06Signs of sepsis and what they mean (simplified)

Sign	What it may mean	What to do
Very fast or difficult breathing	The lungs and circulation are struggling	Emergency services now
Confusion, slurred speech, sleepiness	The brain is not getting enough oxygen	Emergency services now
Pale, grey, bluish or blotchy skin	Circulation has weakened	Emergency services now
Very little urine	The kidneys may be affected	Call straight away
Dizziness, fainting	Blood pressure has fallen	Emergency services now
Very high or low temperature, shivering	A serious infection	During neutropenia, call straight away

* Not all signs appear at the same time. If you suddenly feel very unwell, do not wait for the full list of signs; get help.

07Key terms

Sepsis: A dangerous condition in which an excessive immune response to infection damages organs.
Septic shock: The most severe form of sepsis, when blood pressure has to be supported with medicines.
Neutropenic sepsis: Sepsis that develops while neutrophils are low.
Organ dysfunction: An organ, such as the kidneys, lungs or brain, not working properly.
SOFA: A score that rates how well six organ systems are working.
NEWS2: A risk score based on breathing, oxygen, blood pressure, pulse, alertness and temperature.
Lactate: A substance that rises in the blood when tissues are short of oxygen.
Vasopressor: A medicine that tightens blood vessels and raises blood pressure.
Source control: Removing the site of infection, for example taking out a catheter.
Post-sepsis syndrome: Physical and psychological symptoms that can last for months after sepsis.

08Key points

Sepsis is the body’s excessive response to infection, and it damages organs.
Any infection can lead to sepsis.
During neutropenia, sepsis can develop faster.
The temperature can be high or low.
Confusion, fast breathing, blotchy skin and little urine are emergency signs.
Antibiotics start as soon as possible, ideally within one hour.
Recovery after sepsis can take weeks and months.
If in doubt, do not wait: get help straight away.

09Frequently asked questions

Is sepsis contagious?

Sepsis itself is not contagious. But the infection that caused it, such as flu, can pass to others. Your loved ones’ hand hygiene and vaccinations help protect you.

Can you have sepsis without a fever?

Yes. Especially in older people and people with weak immunity, the temperature can be normal or below 36 °C. Confusion, fast breathing or sudden weakness can also be signs of sepsis.

Can sepsis start at home?

Yes. According to the CDC, most cases of sepsis start before the person reaches hospital. That is why it is important to keep a thermometer, your team’s number and a short treatment information card at home.

Can you recover fully from sepsis?

Yes, most people recover, especially when treatment starts early. For some, recovery takes months and needs extra support. Tell your team about lasting tiredness, memory problems or mood changes.

Will sepsis delay my leukemia treatment?

Sometimes the next course is postponed until your condition is stable. Doctors weigh the infection risk against the importance of leukemia treatment and make an individual decision.

What should I do if I am kept waiting a long time at the emergency department?

Say again, clearly, that you are having leukemia treatment, give the date of your last chemotherapy and the possibility of neutropenia. If you get worse, tell staff at once and contact your team.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

Which early signs of sepsis should I watch for?
If we suspect sepsis, where should we go and how quickly?
How is sepsis treated in hospital?
What is recovery like after sepsis?

My questions

12Sources

World Health Organization (WHO). Sepsis (fact sheet)
Centers for Disease Control and Prevention (CDC). About Sepsis
NHS (UK). Sepsis
MedlinePlus (U.S. National Library of Medicine). Sepsis
National Institute for Health and Care Excellence (NICE). Suspected sepsis in people aged 16 or over: recognition, assessment and early management (NG253)
National Institute for Health and Care Excellence (NICE). Neutropenic sepsis: prevention and management in people with cancer (CG151)
Cancer Research UK. Sepsis, infection, and cancer
JAMA, 2016. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)
Critical Care Medicine, 2021. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021
Lancet, 2020. Global, regional, and national sepsis incidence and mortality, 1990–2017: analysis for the Global Burden of Disease Study
JAMA, 2018. Enhancing Recovery From Sepsis: A Review
Critical Care Medicine, 2006. Duration of hypotension before initiation of effective antimicrobial therapy is the critical determinant of survival in human septic shock
Annals of Oncology (ESMO), 2016. Management of febrile neutropaenia: ESMO Clinical Practice Guidelines

Medical disclaimerThis information is for educational purposes only and does not replace medical advice.

Last updated: 3 October 2026← Back to the list

Open the interactive site →