Neonatal listeriosis

Listeriosis is an infection caused by the bacterium Listeria monocytogenes (L. monocytogenes)¹. Neonatal listeriosis refers to listeriosis that can be found in newborns ( neonates²).³

One can distinguish between early-onset and late-onset neonatal listeriosis. In early-onset neonatal listeriosis, the newborn displays symptoms of the infection very shortly after birth. On average, these symptoms occur 36 hours after birth. In contrast, the symptoms of a late-onset neonatal listeriosis usually appear between 5 days and several weeks after birth⁴.

Frequency of neonatal listeriosis

Neonatal listeriosis is the most common form of listeriosis.³ Unfortunately, it is estimated that up to 50% of all cases of neonatal listeriosis can end fatal.^5,6,7 Reports suggest that the incidence rates tend to vary between countries. In the Netherlands, the UK and the USA, neonatal listeriosis is found about 1.3, 5 and 8.6 times per 100.000 live births, respectively.⁵

Transmission of neonatal listeriosis

Neonatal listeriosis is caused by a bacterium called L. monocytogenes.¹

The infection mostly occurs when mothers infected with L. monocytogenes (maternal listeriosis) pass the infection on to their children (neonatal listeriosis). This is possible because, despite being infected, the mothers can be asymptomatic (not show any symptoms).³

The infection can be transmitted from mother to child while the child is still in the womb and also during labour.^{3, 4} The likelihood of this mother-child transmission happening is hard to estimate. One very extensive study showed that 68% of the newborns with L. monocytogenes infected mothers contracted neonatal listeriosis.⁸ here were instances where supplies (e.g. mineral oil)⁹ or hospital equipment contaminated by L. monocytogenes caused neonatal listeriosis infections.^3,4

Listeriosis is not contagious. Therefore, with the mother-child infection route, one person with listeriosis cannot infect someone else by accident.¹

Cause of maternal listeriosis

The main cause of maternal listeriosis are foods or drinks contaminated with L. monocytogenes bacteria. For example, hot dogs and certain cheeses are often found to be affected by this type of contamination.⁴

It is estimated that the time from the listeriosis infection to showing symptoms is about 3 weeks although in some cases it can be up to several months.^1,4 This is known as the incubation period. 

Unfortunately, it has been found that pregnant individuals are 18 times more likely to contract listeriosis than everyone else. The risk and the occurrence of a maternal listeriosis infection is highest in the third trimester of pregnancy although it can also happen before that. 

Maternal listeriosis can cause the baby to be born premature. More seriously,, a maternal listeriosis infection earlier in the pregnancy commonly results in abortion or stillbirth.⁴

The higher likelihood of a listeriosis infection in pregnant women in the 3rd trimester can potentially be attributed to a slightly impaired immune system during that time.^3,4

L. monocytogenes evades the human immune system by hiding inside certain cells, including some cells of the immune system. Therefore, it tends to take the immune system a while to adapt and mount an appropriate response to repel this unwelcome visitor. Once a person’s immune system has gone through this process, they have a far better protection from L. monocytogenes for a certain period of time.⁴

Consequences of maternal and neonatal listeriosis

Maternal listeriosis clinical features

Maternal listeriosis is generallymilder than neonatal listeriosis.⁴ Flu-like symptoms,¹⁰ fever or no symptoms at all (asymptomatic) are seen most frequently.⁸

Early-onset neonatal listeriosis clinical features^3,4

• Septicaemia¹¹ 
• Sepsis¹² Respiratory distress¹³ 
• Asphyxia¹⁴ Pneumonia¹⁵ Meningitis¹⁶ Late-onset neonatal listeriosis clinical features⁴

Septicaemia¹¹ (Sepsis¹²Meningitis¹⁶ Symptoms of neonatal listeriosis

Symptoms of neonatal listeriosis include:¹

• Difficulty breathing (short and fast breaths and wheezing)
• Fever
• Vomiting
• Persistent crying
• Lack of appetite

Diagnosis of neonatal listeriosis

The diagnosis of neonatal listeriosis usually involves retrieving certain samples from the newborn baby and then trying to identify L. monocytogenes in these samples using various methods including microscopy.

The samples taken from the newborn might be:^1,4,8

• Blood
• Cerebrospinal fluid¹⁷ 
• A swab run over sites such as the ear, the skin or the conjunctiva¹⁸ 
• Vomit
• Meconium¹ 

Treatment of neonatal listeriosis

The treatment for a bacterial infection such as neonatal listeriosis is the use of antibiotics, often two at the same time.

Which antibiotics are chosen and in which combination depends on the attributes of each antibiotic and if they meet the requirements for therapy in each individual case. For example, in some cases L. monocytogenes has managed to invade the newborn’s central nervous system which can lead to meningitis¹⁶. Therefore, the antibiotic(s) used need to have the ability to enter the central nervous system to eradicate L. monocytogenes there as well.^3,4

Occasionally, other measures might need to be taken in an emergency. For example, if the newborn child is having difficulty breathing or is suffocating, an endotracheal intubation¹⁹ could be necessary.³ This involves inserting a plastic tube through the mouth or nose down into the windpipe to improve or restore unassisted breathing or to allow assisted breathing with the help of machines.¹⁹

Prevention of neonatal listeriosis

L. monocytogenes vaccine

Unfortunately, there is currently no vaccine available to protect against Listeria monocytogenes infections. Promising efforts in biomedical research are underway looking into the possibility of such a L. monocytogenes vaccine.²⁰

Treatment of maternal listeriosis

One of the ways of preventing neonatal listeriosis is diagnosing and treating maternal listeriosis with antibiotics as soon as possible. The earlier the treatment takes place, the better for the unborn child. For the best results, treating maternal listeriosis with high doses of the antibiotic ampicillin for the duration of 2 weeks is recommended.⁴

In cases of severe maternal listeriosis with septicaemia.¹¹ the antibiotic treatment might be combined with a deliberate delay of the birth so the antibiotics have more time to take effect. It has been shown that this approach can result in the birth of a healthy child without neonatal listeriosis despite the mother’s grave listeriosis infection.⁴

Prevention of maternal listeriosis

The best way to guard against neonatal listeriosis is to prevent maternal listeriosis. In order to do so, certain precautions need to be taken by and for pregnant women.

Pregnant women should avoid consuming:^1,21,22,23

• Unpasteurised milk
• Unpasteurised and pasteurised uncooked mould-ripened soft cheese 
• Unpasteurised and pasteurised uncooked blue cheese 
• Some dairy products made of unpasteurised milk (e.g. ripened goats' cheese)
• Uncooked deli cheeses
• Unpasteurised juice
• Refrigerated meats (pureed meat/pâté including vegetable pâté) 
• Refrigerated meat spreads from a deli or from a meat counter in a supermarket
• Uncooked cured or cold-smoked fish (e.g. gravlax or smoked salmon)
• Seafood, deli meats, egg dishes and hot dogs if not properly cooked 
• Recent leftovers that are not properly heated
• Leftovers that are a few days old

Pregnant women can fairly safely consume:^1,21,22,23

• Pasteurised milk
• Pasteurised soft cheese (e.g. halloumi and feta)
• Unpasteurised and pasteurised soft cheeses and blue cheeses if strongly heated until they are steaming hot
• Unpasteurised and pasteurised hard cheese (e.g. parmesan and certain cheddars)
• Pasteurised semi-hard cheese 
• Deli cheeses if strongly heated until they are steaming hot
• Pasteurised juice
• Shelf-stable or canned meat spreads and pureed meat/pâté (these need to be refrigerated immediately after opening)
• Cured or cold-smoked fish (e.g. gravlax or smoked salmon) if strongly heated until they are steaming hot
• Seafood, deli meats, egg dishes and hot dogs heated to at least 74 °C
• Recent leftovers (less than a few days old) if strongly heated until they are steaming hot

Proper hygiene needs to be observed when handling and cooking food including:¹

• Thoroughly cleaning all surfaces the food comes in contact with (before and after cooking)
• Thoroughly washing hands (with soap and water before, whenever necessary and after cooking)
• Using only clean kitchen utensils to prepare food
• Thoroughly cleaning fruits and vegetables Properly storing food in the refrigerator (wrapped in foil/plastic wrap or placed in clean containers with a cover or plastic bags)
• Making sure things like raw meat do not leak onto and thereby contaminate other foods
• Immediately cleaning any spills in the refrigerator (spills of meat juices are particularly dangerous)

FAQ’s

How can I prevent listeriosis during pregnancy?

The best way to prevent listeriosis during pregnancy (maternal listeriosis) is to avoid eating and drinking certain things that have a high risk of being contaminated with L. monocytogenes which is the cause of listeriosis. 

How would a newborn get listeria?

A newborn is most likely to get Listeria from the mother if the mother is infected with Listeria herself. The infection normally occurs before or during birth.

What does listeria do to a baby?

A baby infected with Listeria monocytogenes is likely to develop one or several serious, life-threatening conditions which can be fatal.

Can listeria pass through breastmilk?

It is not known if Listeria can be passed to the breastfeeding child via breastmilk. If that is a possibility, the likelihood of it actually happening is believed to be low.²⁴

Summary

Neonatal listeriosis is a serious infection in the newborn caused by the L. monocytogenes bacterium, It is brought on by the maternal listeriosis which spreads to babies before or during birth. Infection of the unborn child with listeriosis can lead to abortion and stillbirth while listeriosis in newborns (neonatal listeriosis) can result in a number of serious, life-threatening conditions. 

Antibiotics are the treatment of choice for both maternal and neonatal listeriosis.

The best way of avoiding neonatal listeriosis is preventing maternal listeriosis. Maternal listeriosis mostly occurs due to the consumption of food or drink contaminated with L. monocytogenes by pregnant women. Therefore, refraining from ingesting certain high risk foods and drinks and taking other precautions during pregnancy is the most effective way of preventing neonatal listeriosis.