Causes - Sepsis

Sepsis can affect multiple organs or the entire body.

Bacterial infections are the most common cause of sepsis. Viral or fungal infections can also cause sepsis.

An infection can trigger sepsis in any part of the body. The most common sites of infection leading to sepsis are the lungs, urinary tract and tummy.

Sepsis may develop when you're already in hospital.

You're more likely to develop sepsis if you:

  • are on immunosuppressive treatment
  • recently had surgery
  • had an indwelling catheter or other catheter fitted, for example, a urinary catheter

Types of infection

Types of infection associated with sepsis include:

  • lung infection (pneumonia)
  • appendicitis
  • an infection of the thin layer of tissue that lines the inside of the abdomen (peritonitis)
  • an infection of the bladder, urethra or kidneys (urinary tract infection)
  • an infection of the gallbladder (cholecystitis) or bile ducts (cholangitis)
  • skin infections, such as cellulitis - these can be caused by a catheter that's been inserted through the skin to give fluids or medication
  • infections of the brain and nervous system – such as meningitis or encephalitis
  • bone infection (osteomyelitis)
  • heart infection (endocarditis)
  • viral infections

Sometimes the specific infection and source of sepsis cannot be identified.

Infections and sepsis

Usually, your immune system keeps an infection limited to one place. This is known as a localised infection.

Your body produces white blood cells. These travel to the site of the infection to destroy the germs causing infection.

Inflammation helps fight the infection and prevents it from spreading.

If your immune system is weak or if an infection is severe, it can quickly spread through the blood into other parts of the body. 

This causes the immune system to go into overdrive and the inflammation affects the entire body.

Changes in blood flow can lead to a fall in blood pressure and this can lead to a reduction in blood flow and oxygen reaching your organs and tissues

People at risk

Everybody is at risk of developing sepsis from minor infections.

Some people are more at risk of sepsis, including:

  • babies younger than 1 year
  • people over 75
  • people who are frail
  • people with diabetes
  • people with weak immune systems
  • people who are having chemotherapy treatment
  • women who have just given birth or recently been pregnant - including those who have had a miscarriage or abortion
  • people who have recently had surgery
  • people who have recently had a serious illness

If you're already in hospital for another serious illness, you have more chance of developing sepsis.

Bacterial infections such as MRSA that can be caught in hospital tend to be more serious. These bacteria have often developed a resistance to many commonly used antibiotics.

Read about treatment for sepsis


Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

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