NHS hospitals must adopt an early warning system to prevent nearly 2,000 avoidable deaths caused by conditions including sepsis, according to officials.

Sir Bruce Keogh, the NHS medical director, said that every hospital must use a national scoring system by 2019 to identify patients who require urgent intervention. This could prevent the risk of death or deterioration of millions of patients, The Telegraph reported.

Senior doctors noted that being vigilant of warning signs including a patient's heart rate, blood pressure, temperature and breathing, were particularly useful in diagnosing sepsis.

So what is the condition that is the second biggest killer in the UK after heart disease, and claims the lives of more people than bowel, breast and prostate cancer each year – combined?

What is sepsis?

Sepsis is the term used to describe a rare but serious complication caused by an infection that causes the immune system to go into overdrive. This triggers swelling, inflammation and blood clots. If untreated, a patient's blood pressure will drop, cutting off blood supply to their vital organs – eventually resulting in death. This can happen in a matter of hours.

What are the symptoms?

According to the NHS, the condition causes different symptoms depending on a person's age. In children under five, the skin may turn a mottled, bluish or pale colour; they may become lethargic and difficult to wake up, and their breathing noticeably fast. A rash that doesn't fade when it is pressed can form, and/or the skin may be cold to the touch. Sepsis can also cause fits and convulsions.

Older children and adults may experience a fever; chills and shivering; a quick heartbeat and fast breathing. If severe sepsis – known as septic shock – sets in, a person can feel dizzy; become confused; and experience diarrhoea, nausea and vomiting. Slurred speech, severe muscle pain and breathlessness are also signs. Someone with sepsis may also produce less urine, and their skin can become cold, clammy or mottled.

The NHS urges anyone who suspects they or someone else has sepsis – particularly after an infection or injury – to seek urgent medical advice.

"Severe sepsis and septic shock are medical emergencies. If you think you or someone in your care has one of these conditions, go straight to A&E or call 999," the NHS website advises.

How is it treated?

Spotted early before it affects the vital organs, the infection can be treated with a round of antibiotics and patients can make a full recovery. Those who experience severe sepsis and septic shock will need hospital treatment, and may be admitted to the intensive care unit. If blood clots form, dead tissue will need to be removed. This means sepsis can lead to amputations and the removal of all or parts of organs.

Who is at risk?

Anyone can get sepsis, but those who have serious wounds from surgery or an injury; with weakened immune systems; and the very young or old are most vulnerable.