Necrotizing Enterocolitis (NEC)

What is NEC?

Necrotizing enterocolitis, or NEC, is a common disease of the intestinal tract in which the tissue lining the intestine becomes inflamed, dies, and can slough off.

The condition typically affects infants who are born preterm or who are already sick, and it usually occurs before the newborn leaves the hospital.¹

NEC usually begins within the first 2 or 3 weeks after birth in preterm infants who otherwise appear to be getting healthier.²

In NEC, some of the tissue lining an infant’s intestine becomes diseased and can die. The bacteria in the infant’s intestine can then penetrate the dead or decaying intestinal tissue, infect the wall of the intestine, and enter the bloodstream, causing systemic or bloodstream infection. The surviving tissue becomes swollen and inflamed; as a result, the infant is unable to digest food or otherwise move food through the digestive tract.¹

The symptoms of NEC can develop over a period of days or appear suddenly. Commonly reported symptoms include^2,3:

• Poor tolerance of feeding (not being able to digest food)
• Bloating or swelling of the stomach (abdominal distention)
• Stomach discoloration, usually bluish or reddish
• Pain when someone touches the abdomen
• Blood in the stools or a change in their volume or frequency
• Diarrhea, with change in the color and consistency of the stool, often containing frank (visible) blood
• Decreased activity (lethargy)
• Vomiting greenish-yellow liquid
• Inability to maintain normal temperature
• Episodes of low heart rate or apnea, a temporary stop in breathing
• In advanced cases, the blood pressure may drop and the pulse may become weak. Infants may develop fluid in the abdominal cavity or infection of the tissue lining the stomach (a condition called peritonitis), or they could go into shock.³ The affected area of the intestine may develop a hole or perforation in the wall requiring emergency surgery.^2,3 Pressure from the abdomen can cause a severe difficulty in breathing. In this case, the infant may need support from a breathing machine, or respirator.

According to a 2008 review of the evidence, all newborn infants born preterm (before 37 weeks of pregnancy) or born with a low birth weight (less than 2,500 grams, or about 5.5 pounds) are at increased risk for NEC. The smaller the infant or the more premature the delivery, the greater the risk.¹

The Centers for Disease Control and Prevention’s (CDC) National Center for Health Statistics (NCHS) in 2019 listed NEC as one of the 10 leading causes of infant mortality.² For recent data, please access the NCHS-compiled data on linked birth/infant death records in the United States, including underlying causes of death such as NEC, from CDC’s Wide-ranging ONline Data for Epidemiologic Research (WONDER) database.

The population most at risk for NEC is increasing because with technological advances in care the number of very low birth weight (VLBW) infants who survive continues to grow.¹ The percentage of VLBW infants who develop NEC remains steady, however, at about 7%.¹

Although NEC mostly occurs in preterm infants, it occasionally occurs in infants born at term. One study found that about 9% of all NEC cases that occurred in one children’s hospital over 30 years were in full-term infants.³ Full-term infants with NEC often have another serious illness or risk factor, such as congenital heart disease or restricted growth in the womb. NEC may also have a different disease process in full-term versus preterm infants.¹

The development of symptoms such as the inability to tolerate feeding, bloody stools, or distention of the abdomen could indicate NEC. The condition is usually confirmed by an abdominal X-ray. If the X-ray reveals a “bubbly” appearance in the wall of the intestine or air outside the infant’s intestine (in the peritoneal cavity) the diagnosis is confirmed.¹ Other X-ray signs include air in a vein of the liver called the portal vein, swollen intestines, or a lack of gas in the abdomen.

Other useful tests include looking for blood in the infant's stool. If necessary, the healthcare provider can use a chemical that reveals blood not visible to the eye.

In addition, healthcare providers may test the infant's blood to check for infection, which could suggest NEC. They may also use a blood test for lactic acid, which can indicate whether the body is getting enough oxygen or an infection that increases the metabolic rate and production of lactic acid.²

Blood and stool tests, combined with the abdominal X-ray, can help the healthcare provider determine the seriousness of the infant's condition.

The treatment for NEC varies with the severity of the disease. Three stages (Bell stages) have been defined for NEC.¹

• Stage 1, suspected NEC, includes symptoms such as bloody stools, diminished activity (lethargy), slow heart rate, an unstable temperature, mild abdominal bloating, and vomiting.
• Stage 2, definite NEC, includes all the symptoms of stage 1 as well as slightly reduced blood platelet levels, a slight excess of lactic acid, no bowel sounds, pain when the abdomen is touched, reduced or no intestinal movement, and the growth of gas-filled spaces in the walls of the intestine.
• Stage 3, advanced NEC, includes the symptoms of stages 1 and 2 plus periods of not breathing, low blood pressure, a lowered number of certain white blood cells, blood clot formation, a stop in urination, inflammation of tissue in the abdomen, increased pain when the abdomen is touched, redness in the abdomen, a build-up of fluid and gas in the abdominal cavity, and excess acid.

The treatment for stage 1 patients includes vigorous supportive care, resting the intestine by feeding through an intravenous tube instead of the mouth, and continued diagnostic and monitoring tests to ensure that the disease is not progressing. Treatments for stage 2 patients include continuation of stage 1 treatments and the use of antibiotics. Emergency surgery is sometimes performed for stage 3 patients.²

Other treatments³ offered at all stages of NEC include:

• Inserting a tube through the nasal passages or mouth into the infant’s stomach to remove air and fluid
• Taking blood samples to look for bacteria and giving antibiotic treatment through an intravenous tube
• Measuring and monitoring the infant’s belly for swelling. If it becomes so swollen that it interferes with breathing, the infant may be given oxygen or put on a ventilator.

Many infants respond to treatment within 72 hours, and physicians may decide to put these infants back on regular feeding. (Generally, infants are not fed for up to 2 weeks or longer with confirmed NEC.) However, if the condition worsens or a hole develops in the intestine or bowel, surgery may be needed.³

The cause of NEC is not well known.^1,2 In premature infants, the cause may be related to the immaturity of the child’s digestive system. NEC involves infection and inflammation in the child’s gut, which may stem from the growth of dangerous bacteria or the growth of bacteria in parts of the intestine where they do not usually live.^1,2

Other possible causes of NEC that are related to having an immature gut include²:

• Inability to digest food and pass it through, allowing a buildup of toxic substances
• Inadequate blood circulation to the gut
• Inability of the infant’s digestive system to keep out dangerous bacteria
• Inadequate ability of the immature intestine to provide an adequate structural barrier to bacteria. This barrier usually matures in the unborn infant starting about week 26 (11 to 12 weeks before a full-term birth).
• The inability of the immature gut to secrete its normal biochemical defenses

Because premature infants may lack any or all of these abilities, they may be more vulnerable to the types of inflammation that lead to NEC.²

Full-term infants who get NEC almost always do so because they are already sick or, in some cases, have a low body weight for their gestational age. They might have congenital heart disease or have had vascular bypass surgery, for example, possibly affecting the blood supply to the intestines.²

Full-term infants are usually diagnosed with NEC earlier than are premature infants (day 5 versus day 13 on average), possibly because they start feeding earlier. The condition is equally life threatening in premature and full-term infants.³

A recent NICHD-supported study found that a common type of medication, sometimes given to infants for acid reflux and called “H2-blockers,” was associated with a slight increase in the risk of NEC in preterm infants.⁴