Listeria Infection in Pregnancy

Listeriosis is an infection caused by Listeria monocytogenes.Up to one in twenty adults have this bacterium in their feces, so the infection is a fecal-oral route, much like the feline-caused Toxoplasmosis, and is probably everywhere.  Foods contaminated with Listeria, like soft cheeses and unpasteurized products and cold cuts, can cause outbreaks, but in pregnancy it can have no symptoms at all or cause an illness that may be confused with a urinary tract infection or with just a flu that is managed with fluids and tylenol.


In pregnancy, this maternal infection can also infect the baby:

  • If contracted early, it can cause miscarriage.  If the infection occurs later on, it can cause Intrauterine Growth Restriction (IUGR).
Other infectious causes for IUGR include viral infections like Rubella, Cytomegalovirus, Hepatitis A and B, influenza, and chicken pox.  Tuberculosis, a bacterial infection, and syphilis (caused by an organism called a spirochete) also cause IUGR.
  • In the third trimester, Listeria can be a cause for premature labor, premature delivery, and ultimately can cause neonatal sepsis, meningitis, and death--a baby-killer.  The meningitis in the baby can even develop after the first few weeks of life.


In private practice it is an infection that is easily missed.  It is a fairly weakly infectious bacterium, usually seeking out theimmuno-compromised, like persons with AIDS...or pregnancy.

Frequency of Listeria Infections in Pregnancy

It is felt that exposure to it usually will not cause infection, because it is so common a germ.

The true frequency of infection and infection affecting pregnancy is unknown for several reasons.  Few obstetricians get routine cultures on miscarriages, assuming correctly that miscarriage is usually the result of genetic mishaps, especially in the absence of maternal symptoms.  Because it is not checked for scrupulously and because it seems to be everywhere in contaminated products, the epidemiology statistics are still quite a mess.

Listeria in pregnancy usually appears as flulike, which can be scary when almost every pregnant woman gets flu-like symptoms at some point in her pregnancy.  Low grade fever, headache, and  muscle pain are common, but there may be no symptoms at all.  Less commonly there can be diarrhea and cramps.

The mother may suffer minimally, but the baby's situation is life-threatening. 


Delivery usually unloads the largest amount of the infection from the mother's body, causing immediate improvement.  Treatment of the mother may or may not help the undelivered baby.  In the past, a combination of Ampicillin (a broad spectrum penicillin) and Gentamycin (an antibiotic classified as an "aminglycoside") has been used.  But the onset of premature labor in a baby already seen compromised will have an obstetrician weighing the risk vs. benefit of delivery.  Certainly delivery is indicated in the late third trimester so that treatment can be attempted on the newborn.  In cases of severe prematurity, there is no "best" answer for a difficult question.

In the real world, obstetricians don't obtain blood cultures and other tests for Listeriosis on every woman with a low grade fever, headache, or muscle aches.  They can't.

A case study:

A pharmacist's wife I had been caring for came in for a routine visit at about 37 weeks.  She claimed some vague change in fetal movement had occurred.  The ultrasound didn't show anything worrisome, but just to be ridiculously (I thought) overcautious, I had her undergo a fetal non-stress test.  The test was somewhat reassuring, but not perfect, so I sent her to the hospital for a contraction stress test.  With each contraction induced, there was a deceleration of the fetal heart rate.  More alarmingly, it was what is called a "late" deceleration, indicating that not only did the baby not have a lot of reserve for stress, but also was reacting to stress in a delayed way, indicative of fetal distress.  Besides this test indicating that the baby could not tolerate a labor, the patient's Bishop's score was not favorable, so any labor would be a lengthy one at that.

At C-section, there was a lower than normal APGAR score, but it improved at 5 minutes and the baby ultimately did fine.  I obtained cultures on both sides of the placenta and of the amniotic fluid at the time of surgery, and the results grew out Listeria.  Mom and Dad gave me a ceramic angel to hang up in our non-stress test exam room, where I always think about Listeria when things aren't quite right.

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