An overview

What is NEC?

Necrotizing enterocolitis (NEC) is a serious disease that affects the intestines (bowels or guts) of newborn babies. Necrotizing refers to the death of cells and tissue, and enterocolitis means inflammation of the intestines. In its most severe form, NEC can cause an  inflammatory response throughout the body and septicemia.

Babies most at risk of developing the disease are those born before 32 weeks or with a birth weight less than 1500g. NEC can affect babies born at term, but such cases are rare and there are usually other medical problems such as heart conditions and abnormalities of the bowel. More babies are at risk of NEC as the survival rates of those born extremely prematurely continue to improve.

The causes of NEC, how it develops and why some babies and not others get it are not yet fully understood. It is a complex, unpredictable disease of immaturity that can develop suddenly in infants who appeared to be quite stable. There is no reliable non-invasive test and it is suspected more frequently than it actually occurs. It can involve both the small and large bowel, though the small bowel is predominantly affected in most cases.

NEC is not a contagious disease; a baby cannot catch it from another.

In mild and moderate cases, the majority of babies recover with no complications, but approximately one in four babies diagnosed with it will require surgical intervention. NEC requiring surgery has high rates of death (mortality) and long-term disability (morbidity).

Feeding babies with their mother’s own milk gives some protection against NEC because breast milk contains a wide variety of beneficial components. However, it does not totally eliminate the risk.

What are the symptoms?

The timing of when babies show symptoms of NEC depends on their gestation at birth. Babies born extremely prematurely typically develop the disease later than babies born much closer to term.

The highest risk seems to be around 31-32 weeks of corrected age.

Feeding intolerance is the most common early gastrointestinal symptom. Other early symptoms – increased apnoeas and bradycardias, low blood pressure, temperature changes – are signs of generalised illness and infections. A combination of findings provides the most accurate diagnosis. These include:

• increased gastric aspirates from the nasogastric (NG) tube
• swelling, tenderness and discolouration of the tummy and bowel area (abdomen)
• blood in stools (faeces, poo)
• signs on X-ray like gas seen in the wall of the intestine (pneumatosis)
• bringing up bile (a green fluid)

It is extremely difficult to differentiate NEC from another condition, spontaneous intestinal perforation (SIP), and it takes surgical intervention to confirm a diagnosis. NEC may also be confused with volvulus, a condition in which the bowel twists on itself and intestinal tissue is damaged by a lack of blood supply.

How is it treated?

If X-rays, blood tests and a baby’s condition lead to the strong suspicion that it is NEC, the clinical team will treat the baby for ‘medical NEC’. This means stopping milk feeds for 5-14 days and resting the bowels. The baby is given nutrients and antibiotics directly into a vein (intravenously or “a drip”), and supported to breathe when necessary. This is called the conservative management of the baby’s condition.

If the baby improves and is given milk feeds again, it is best to use breast milk. This is because recovering babies tolerate milk from their mum, or a donor, better than formula, which is based on cow’s milk. If breast milk is not tolerated, a special, simpler milk may be tried.

Most babies treated in this way do not have any further concerns or long-term effects.

In severe cases, babies need intensive care and a decision may be taken to operate.

If one or more parts of the intestines becomes irreversibly damaged, their contents spill into the baby’s abdomen and in such cases urgent intervention is needed. Sometimes a small drain is inserted to remove the leaking bowel contents, and surgery under general anaesthetic is performed later. Alternatively, surgery is performed immediately;  the parts of the bowel that have died are removed and healthy sections are joined together. In extreme cases, the whole bowel can be affected.

If surgical facilities are not available in the same hospital as the neonatal unit caring for the baby, the baby will require a transfer to another hospital by a specialist transport team.

What are the outcomes?

In the short term, about a quarter of babies suffer complications related to surgery¹, but the long-term outlook depends on how much of the bowel had to be removed. Some children may grow up with mild symptoms relating to tolerance of foods or frequency of bowel movement, while others can suffer serious problems. These include growth delay, cerebral palsy and short bowel syndrome – a condition which makes it more difficult to absorb the nutrients in food.

In the worst cases, necrotizing enterocolitis develops so rapidly that babies are too sick to undergo surgery or transfer to another hospital. Some may not survive surgery. The mortality rate can be as high as 50%.

How many babies get NEC?

Most of the information available on NEC is from North America and the United Kingdom, but NEC occurs anywhere that premature and sick babies are cared for in neonatal units.

It is difficult to say for certain how many babies born in different countries have been affected by NEC due to the lack of data, differences in how NEC is defined and treated, differences in culture and the low numbers of post mortems carried out.

There is no national system collecting data on NEC in the UK, but it is estimated² that there are up to 1,000 cases each year and two large national studies of severe NEC provide the most reliable data.

The first study³ gathered data from every neonatal unit in England between 1 January 2012 and 31 December 2013. It showed that 531 babies had severe NEC, which was 0.45% of all the babies who were admitted to neonatal care. More than half of those babies (53%) survived to discharge and the majority of severe cases (87%) occurred in babies who were born before 32 weeks. NEC accounted for 12% of all deaths of babies who needed neonatal care in that period, and 90% of the babies who died of NEC were born before 32 weeks.

The second study¹, which took place between 1 March 2013 and 28 February 2014, looked at the number of infants in the UK and Ireland where a decision was made to operate. It found an incidence of 27.9 cases of severe NEC per 100,000 live births.

In North America, it is estimated that NEC affects babies at a rate of 1-3 per 1000 births⁴.

In summary:

More detailed information on NEC can be found in the next sections.

Sources
1. A UK wide cohort study describing management and outcomes for infants with surgical Necrotising Enterocolitis
B. Allin, A-M. Long, A. Gupta, M.Knight, K. Lakhoo & British Association of Paediatric Surgeons Congenital Anomalies Surveillance System Necrotising Enterocolitis Collaboration
Scientific Reports 7, Article number: 41149 (2017), Published online: 27 January 2017
2. UK Neonatal Collaborative NEC Study Group (UKNC-NEC)
3. Incidence and enteral feed antecedents of severe neonatal necrotizing enterocolitis across neonatal networks in England, 2012-13: a whole-population surveillance study.
C. Battersby, N.Longford, S. Mandalia, K.Costeloe, N.Modi.
Published online 7 November 2016