Sepsis is commonly described as having three stages: sepsis, severe sepsis and septic shock. Although it is not the formal way sepsis is classified today, it is still a useful way to understand how the condition can become more serious.

Current guidance defines sepsis itself as a life-threatening condition involving organ dysfunction, while septic shock remains the term for a particularly serious form of sepsis. 

This guide explains what people usually mean by Stage 1, Stage 2 and Stage 3 sepsis, how sepsis progresses, why early diagnosis and urgent treatment matter, and when you might be able to make a sepsis medical negligence claim.

The 3 stages of sepsis at a glance

Although these terms are no longer formally used, the three stages of sepsis are commonly described in the following way:

These stages of sepsis are best understood as descriptions of increasing severity, rather than three fixed steps everyone passes through. Sepsis can progress rapidly, and the pattern will vary depending on the underlying infection, the person's health and their response to medical treatment.

Does sepsis really have 3 stages?

Older medical definitions separated sepsis, severe sepsis and septic shock, and used systemic inflammatory response syndrome (SIRS) to identify a widespread inflammatory response to infection.

Current definitions instead focus on how infection affects organ function and the body's response. Severe sepsis is no longer a separate formal category, and systemic inflammatory response syndrome is no longer used to define sepsis. Current NICE guidance on suspected sepsis assesses risk of severe illness or death rather than assigning a Stage 1, Stage 2 or Stage 3 classification.

What does stage 1 sepsis mean?

When people use the term Stage 1 sepsis, they usually mean sepsis before septic shock has developed, or the earliest recognised part of the illness. Stage 1 is not a formal diagnosis in current guidance, and it should not be taken to mean “mild” sepsis.

Sepsis happens when the body's response to an infection starts to damage its own tissues and organs. The immune system normally protects the body from infection, but in sepsis the immune system response becomes dysregulated and harmful. Sepsis is a medical emergency and needs urgent assessment and treatment.

Sepsis can develop from bacterial infections and, less commonly, viral infections or fungal infections. Risk factors include a weakened immune system or chronic illness. These risk factors increase vulnerability, but a weakened immune system is not required, and sepsis can affect anyone.

How does systemic inflammatory response syndrome relate to stage 1 sepsis?

Systemic inflammatory response syndrome (SIRS) is relevant to Stage 1 because it formed part of the older definition of sepsis. Doctors looked for signs such as changes in temperature, heart rate, breathing rate and white blood cell count. Infection alongside this response could be classified as sepsis.

This broadly corresponds to what many simplified explanations later called Stage 1 sepsis, but SIRS and Stage 1 sepsis are not the same thing. Systemic inflammatory response syndrome can occur for reasons other than infection, so SIRS was not specific enough to identify sepsis reliably. Modern definitions instead focus on organ problems caused by infection.

What are the early symptoms of sepsis?

Sepsis symptoms vary and can overlap with other conditions. According to NHS guidance on sepsis, symptoms of sepsis in adults can include:

• Confusion or slurred speech
• Difficulty breathing or breathing very quickly
• A very high or very low temperature
• Blue, pale, grey or blotchy skin, lips or tongue
• Passing very little urine or not urinating for a long period
• Uncontrollable shivering or severe muscle pain

A person will not necessarily have every symptom. If you think you or someone else may have sepsis, follow NHS advice and seek immediate medical attention rather than trying to decide which stage the condition has reached.

For more detail on early signs, read our guide to the early warning signs of sepsis.

What does stage 2 sepsis mean?

Stage 2 sepsis usually refers to what older medical definitions called severe sepsis. This meant that sepsis was accompanied by significant organ dysfunction.

Under current definitions, severe sepsis is no longer a separate category because problems with organ function are already part of sepsis.

What was severe sepsis?

Historically, severe sepsis described sepsis where one or more vital organs were no longer working normally. The kidneys, lungs, brain, liver and cardiovascular system could all be affected. Now, this type of organ failure falls under the standard definition of sepsis.

Sepsis leads to decreased blood flow, which can mean tissues and vital organs receive less oxygen. Possible signs include:

• Passing much less urine, which can indicate acute kidney injury and may progress to kidney failure
• Increasing difficulty breathing or problems affecting the respiratory system
• Confusion, drowsiness or other changes in mental state
• Low blood pressure or signs of reduced blood flow around the body
• Changes in skin colour or temperature as circulation becomes impaired

Doctors and nurses assess these signs alongside observations and blood tests. These may include lactate measurement, kidney function tests and blood cultures to support sepsis diagnosis and investigate the underlying infection.

Can you recover from Stage 2 sepsis?

People can recover from sepsis even when serious organ problems have developed, although recovery varies. Recovery can take weeks or months, and some people experience post-sepsis syndrome, including fatigue and problems with concentration. Post-sepsis syndrome does not affect everyone, and surviving sepsis is different for each person.

What does stage 3 sepsis mean?

Stage 3 sepsis is commonly used to mean septic shock. Unlike the older terminology associated with Stage 1 and Stage 2, septic shock remains a recognised medical term.

What is septic shock?

Septic shock is a particularly serious form of sepsis involving profound problems with circulation. Blood pressure can remain dangerously low and the body may struggle to maintain blood flow to vital organs, increasing the risk of organ failure.

A person with septic shock may need treatment in an intensive care unit so doctors and nurses can monitor blood pressure, breathing, urine output and kidney function. Sepsis treatment may include intravenous antibiotics, intravenous fluids, medicines to support blood pressure, oxygen and other organ support, depending on the underlying infection and the person's condition.

Septic shock can cause or worsen organ failure. In the most serious cases, several organs may be affected at once, sometimes described as multiple organ failure. Kidney failure, respiratory failure and severe circulatory problems may all require treatment in an intensive care unit.

Can you survive Stage 3 sepsis?

Septic shock is a life-threatening condition requiring emergency treatment and carries an increased risk of serious complications. Outcomes depend on how quickly it is recognised, the underlying infection, the person's health and their response to treatment. Some people who recover experience post-sepsis syndrome or other longer-term effects.

How does sepsis progress and become more serious?

The stages of sepsis are not a fixed order of progression. Sepsis does not always progress neatly from Stage 1 to Stage 2 and then Stage 3, and in some cases it progresses rapidly.

A simple way to understand how sepsis progresses is:

1. An infection develops. Bacterial infections are a common cause, while viral and fungal infections can also trigger sepsis.
2. The body's response becomes harmful. The immune system response becomes dysregulated and starts damaging tissues and organs.
3. Organ function is affected. Problems can develop in the kidneys, lungs, brain or circulation, and reduced blood flow can affect oxygen delivery.
4. Septic shock may develop. Very low blood pressure and severe circulatory problems increase the risk of organ failure.

This is the key difference between the older three stages of sepsis and current medical thinking about sepsis and septic shock: doctors focus on how seriously sepsis is affecting the person rather than placing them on a numbered scale.

What are the signs that sepsis is getting worse?

Symptoms and deterioration matter more than a stage number. Signs that sepsis may be worsening include increasing confusion, difficulty breathing, very low urine output, low blood pressure, changes in skin colour or other signs of organ dysfunction.

NICE guidance considers mental state, breathing, blood pressure, circulation, urine output, temperature and skin changes. In hospital, doctors may also use lactate measurement and blood cultures.

You do not need to identify Stage 1, Stage 2 or Stage 3 before seeking help. If someone is very unwell and you are concerned about sepsis, follow NHS advice on when to get emergency help.

You can also read our guide to the most serious red flag sepsis symptoms.

Why does recognising sepsis deterioration matter?

Early diagnosis and urgent treatment matter because sepsis can quickly become more serious. Doctors and nurses need to assess people with suspected sepsis, monitor changes and respond when their condition deteriorates.

Modern NICE guidance on managing suspected sepsis includes recommendations on repeating clinical observations, carrying out relevant blood tests and escalating care when needed. Sepsis treatment may include intravenous antibiotics, fluids and other medical intervention according to the person's clinical needs.

What matters is that worsening organ dysfunction, poor circulation or septic shock are recognised and acted on appropriately. Delayed treatment allows sepsis to progress and increases the risk of organ failure and other serious complications.

When could delayed sepsis diagnosis or treatment be medical negligence?

A poor outcome after sepsis does not automatically mean that medical negligence occurred. A medical negligence claim requires evidence that the care fell below a reasonable standard and that this caused or contributed to avoidable harm.

Examples that may need investigation include:

• A doctor or nurse failing to recognise symptoms that should have raised concern about developing sepsis.
• A failure to monitor a person appropriately despite signs that their condition was worsening.
• A failure to respond to changes in blood pressure, breathing, urine output or other signs of organ dysfunction.
• An avoidable delay in escalating care as severe sepsis or septic shock was developing.
• An avoidable delay in appropriate sepsis treatment that caused or contributed to additional injury.

JMW uses medical records and independent expert evidence to assess the care and whether different treatment would have changed the outcome. Read our guide to how to prove medical negligence for more information.

How JMW helps with sepsis medical negligence claims

If you are concerned that sepsis was not recognised or treated appropriately, JMW will listen to what happened and advise you on your options.

We start with a free initial consultation. If we recommend investigating your case, we gather GP and hospital records and review the timeline of your care. Where appropriate, independent medical experts assess the standard of care and whether any failing caused avoidable harm.

You can read more about the medical negligence claims process.