Prenatal Infection: Could the Danger be Your Lunch?

Medically Reviewed by Dominic Marchiano and Monica Gandhi

What Do I Have?

Listeriosis is a severe bacterial infection caused by Listeria monocytogenes. This organism is found naturally in soil, decaying vegetation, and in the intestinal tract of most mammals. Approximately 5 to 15% of adults shed this bacterium in their stool.

L. monocytogenes grows well at body (37? C or 98.6? F) and refrigerator (5 to 10? C or 41 to 50? F) temperature. Thus, it can easily contaminate food products as well as various parts of the human body. Listeriosis is spread through the bloodstream.

Approximately 1,000 to 2,000 cases of listeriosis occur each year in the About 20 30% of all cases occur in pregnant women, who can transmit the infection to their babies. The mortality rate from listeriosis is approximately 25%, but may be as high as 50% in newborn babies, those with weakened immune systems (such as those with HIV, cancer, organ transplants, alcoholism, or those on corticosteroid drugs), and in the elderly.

How Is Listeriosis Transmitted?

Most cases of listeriosis occur originally from the consumption of contaminated foods. A variety of foods can be contaminated with this bacterium, including cole slaw, turkey franks, deli meats, and especially chicken. Non-pasteurized dairy products (such as soft cheeses and some varieties of milk) often cause food-borne outbreaks of listeriosis.

When someone ingests contaminated food, L. monocytogenes burrows through the wall of the intestine and spreads by way of the bloodstream to other organs, particularly the brain and placenta (in pregnant women). Direct, person-to-person transmission is unlikely, except from mother to baby.

What Are the Usual Signs and Symptoms of Listeriosis?

Listeriosis may cause several different types of infections, both systemic (affecting the whole body) and localized. These include:

  • bacteremia -People with weakened or suppressed immune functioning often suffer from bacteremia (infection of the bloodstream). Symptoms include fever, malaise (not feeling well), nausea, and vomiting, rapid heart rate, accelerated breathing, hypotension (low blood pressure), and decreased urine output (oliguria);
  • meningitis -Immunocompromised patients who have contracted listeriosis may develop meningitis (inflammation of the membranes of the brain or spinal cord). Besides immunocompromised patients, newborns and the elderly are at risk for Listeria meningitis. Symptoms include high fever, malaise, headache, stiff neck, confusion, gait disturbances, and altered function of the cranial nerves (the major nerves that supply the head and neck with motor and sensory function). Severely ill patients may develop a brain abscess (localized collection of pus);
  • endocarditis -Approximately 5% of patients with listeriosis develop endocarditis (infection and inflammation of the heart valves). This infection usually occurs in people with artificial heart valves, or those with natural valves that have previously been scarred by an infection, such as rheumatic fever;
  • gastrointestinal symptoms -Food-borne listeriosis may cause a gastrointestinal illness characterized by fever, nausea, vomiting, and diarrhea; and
  • other infections -Listeriosis may cause a local infection, such as cellulitis (infection and inflammation of the skin and subcutaneous tissue) or conjunctivitis (infection of the superficial lining of the eye). These infections are relatively minor and are most commonly observed in veterinarians and others who work with animals.

What Special Risks Does Listeriosis Pose During Pregnancy?

Pregnancy suppresses some aspects of immune functioning, which can make you more vulnerable to a range of infections, including listeriosis. When a pregnant woman develops listeriosis, it usually causes bacteremia (bloodstream infection). The most common symptoms are high fever, headache, muscle aches (myalgias), achy joints (arthralgias), and malaise. Some consequences of listeriosis in pregnancy are:

  • intrauterine infection-Once bacteria have infected the bloodstream, they can spread to the placenta. This can lead to chorioamnionitis (an intrauterine infection that involves inflammation of the membrane and sac enclosing the embryo) and may cause multiple, small infections. Symptoms include nausea, vomiting, diarrhea, lower-back pain, pain above the pubic bone, uterine contractions, and discolored vaginal discharge. It may ultimately lead to a miscarriage in early pregnancy or premature rupture of the membranes, preterm labor, and stillbirth later in pregnancy;
  • transmission to the baby-If a pregnant woman develops listeriosis, her baby has a 90% chance of becoming infected. Twenty to twenty-five percent of infected babies die while in the uterus or soon after birth. The earlier in pregnancy the infection occurs, the more likely that it will lead to miscarriage or fetal death. After 20 weeks gestation, listeriosis is more likely to cause preterm labor. Surviving babies with listeriosis usually develop problems similar to those seen in infants infected with GBS;
  • early-onset listeriosis usually occurs within one week of delivery. Affected babies are usually preterm and may have bacteremia, pneumonia, infection of the eye (conjunctivitis), or sores on the skin. A condition known as granulomatosis infantisepticum is an especially serious form of early-onset infection. Babies who develop this condition have widespread infected sores on the skin and small, infected areas in internal organs such as the liver and spleen; and
  • late-onset listeriosis typically occurs one to two weeks after birth and affects term infants. Meningitis is more likely in late-onset than early-onset infection. Bacteremia and pneumonia are the other principal clinical manifestations.

How Is Listeriosis Diagnosed?

Listeriosis is most common in immunocompromised patients (especially HIV patients), newborns or infants, elderly patients, or pregnant women who show signs of meningitis, bacteremia, or severe gastroenteritis.

Your doctor can confirm a suspicion by having a sample from your cerebrospinal fluid, blood, amniotic fluid, or placental tissue cultured (grown) in a laboratory and analyzed for listeriosis. Listeria organisms usually grow readily on culture media within 24 to 36 hours.

Serologic tests (blood tests designed to detect an infectious agent or the antibody to it) or histologic (microscopic) examinations of the infected tissue are not as reliable as cultures for identifying L. monocytogenes. However, an MRI (magnetic resonance imaging) of the brain may reveal signs of infection in the central nervous system.

How Should Listeriosis Be Treated?

If you have meningitis or bacteremia due to listeriosis, you are hospitalized and treated intravenously with the antibiotic drugs ampicillin (Omnipen-N) and gentamicin (Garamycin). An alternative and probably more effective therapy for listeriosis is trimethoprim-sulfamethoxazole. This treatment usually lasts for three to four weeks.. If your heart valves are infected (endocarditis), you are be treated with ampicillin and gentamicin for four to six weeks. You are also monitored with echocardiograms (ultrasound examinations of the heart) periodically to look for abnormal function of the heart valves. If you have a localized infection (such as of the skin or the eye) and are otherwise healthy, you take ampicillin for a short time. For pregnant (and non-pregnant) women who are allergic to ampicillin, trimethoprim-sulfamethoxazole (Septra, Bactrim) is the alternative and may even be more effective than ampicillin.

Treatment of Listeriosis in Pregnancy

If you have listeriosis and are pregnant, your treatment follows the guidelines described above. For mild infections (such as localized infection or gastroenteritis), intravenous ampicillin alone may be enough to kill the infection. But, if your infection is more severe (due to meningitis, endocarditis, or septic abortion), gentamicin is added to your treatment. While being treated, you should temporarily stop taking iron supplements, because iron seems to help the listeria organism grow more readily.

How Can Listeriosis Be Prevented?

Several measures can help to reduce the spread of listeriosis:

  • farmers should process meat, poultry, vegetables, and milk products in as sanitary a manner as possible;
  • raw foods should be kept separate from one another during preparation for cooking. For example, raw meat, chicken, or eggs should not come into contact with raw vegetables;
  • meat and poultry should be cooked completely before being eaten;
  • after a meal is prepared, cooking surfaces should be cleaned thoroughly with soap and warm water;
  • non-pasteurized dairy products (milk, cheese) should be avoided completely; and
  • leftover foods should be re-cooked until they are hot throughout.
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