Listeria infection in pregnancy: A potentially serious foodborne illness

Clinical manifestations of listeriosis

Listeria infections may present with various manifestations, depending on the degree of exposure and the underlying immunocompetence of the host (FIGURE). In its most common and simplest form, listeriosis presents as a mild to moderate gastroenteritis following exposure to contaminated food. Symptoms typically develop within 24 hours of exposure and include fever, myalgias, abdominal or back pain, nausea, vomiting, and diarrhea.⁵

Conversely, in immunocompromised patients, including pregnant women, listeriosis can present as life-threatening sepsis and/or central nervous system (CNS) infection (invasive infection). In this clinical setting, the mean incubation period is 11 days. The manifestations of CNS infection include meningoencephalitis, cerebritis, rhombencephalitis (infection and inflammation of the brain stem), brain abscess, and spinal cord abscess.⁵

In addition to these 2 clinical presentations, listeriosis can cause unusual focal infections as illustrated in the FIGURE. Some of these infections have unique clinical associations. For example, skin or eye infections may occur as a result of direct inoculation in veterinarians, farmers, and laboratory workers. Listeria peritonitis may occur in patients who are receiving peritoneal dialysis and in those who have cirrhosis. Prosthetic joint and graft infections, of course, may occur in patients who have had invasive procedures for implantation of grafts or prosthetic devices.⁵

Listeriosis is especially dangerous in pregnancy because it not only can cause serious injury to the mother and even death but it also may pose a major risk to fetal well-being. Possible perinatal complications include fetal death; preterm labor and delivery; and neonatal sepsis, meningitis, and death.^5-8

Making the diagnosis

Diagnosis begins with a thorough and focused history to assess for characteristic symptoms and possible Listeria exposure. Exposure should be presumed for patients who report consuming high-risk foods, especially foods recently recalled by the US Food and Drug Administration.

In the asymptomatic pregnant patient, diagnostic testing can be deferred, and the patient should be instructed to return for evaluation if symptoms develop within 2 months of exposure. However, symptomatic, febrile patients require testing. The most valuable testing modality is Gram stain and culture of blood. Gram stain typically will show gram-positive pleomorphic rods with rounded ends. Amniocentesis may be indicated if blood cultures are not definitive. Meconium staining of the amniotic fluid and a positive Gram stain are highly indicative of fetal infection. Cultures of the cerebrospinal fluid are indicated in any individual with focal neurologic findings. Stool cultures are rarely indicated.

When obtaining any of the cultures noted above, the clinician should alert the microbiologist of the concern for listeriosis because L monocytogenes can be confused with common contaminants, such as diphtheroids.^5-9

Treatment and follow-up

The treatment of listeriosis in pregnancy depends on the severity of the infection and the immune status of the mother. The TABLE offers several different clinical scenarios and the appropriate treatment for each. As noted, several scenarios may require cultures of the blood, cerebrospinal fluid, and amniotic fluid.^7,9,10

Following treatment of the mother, serial ultrasound examinations should be performed to monitor fetal growth, CNS anatomy, placental morphology, amniotic fluid volume, and umbilical artery Doppler velocimetry. In the presence of fetal growth restriction, oligohydramnios, or abnormal Doppler velocimetry, biophysical profile testing should be performed. After delivery, the placenta should be examined carefully for histologic evidence of Listeria infection, such as miliary abscesses, and cultured for the bacterium.^7-9

Prevention measures

Conservative measures for prevention of Listeria infection in pregnant women include the following^7,10-12:

• Refrigerate milk and milk products at 40 °F (4.4 °C).
• Thoroughly cook raw food from animal sources.
• Wash raw vegetables carefully before eating.
• Keep uncooked meats separate from cooked meats and vegetables.
• Do not consume any beverages or foods made from unpasteurized milk.
• After handling uncooked foods, carefully wash all utensils and hands.
• Avoid all soft cheeses, such as Mexican-style feta, Brie, Camembert, and blue cheese, even if they are supposedly made from pasteurized milk.
• Reheat until steaming hot all leftover foods or ready-to-eat foods, such as hot dogs.
• Do not let juice from hot dogs or lunch meat packages drip onto other foods, utensils, or food preparation surfaces.
• Do not store opened hot dog packages in the refrigerator for more than 1 week. Do not store unopened packages for longer than 2 weeks.
• Do not store unopened lunch and deli meat packages in the refrigerator for longer than 2 weeks. Do not store opened packages for longer than 3 to 5 days.
• If other immunosuppressive conditions are present in combination with pregnancy, thoroughly heat cold cuts before eating.
• Do not eat raw or even lightly cooked sprouts of any kind. Cook sprouts thoroughly. Rinsing sprouts will not remove Listeria organisms.
• Do not eat refrigerated pâté or meat spreads from a deli counter or the refrigerated section of a grocery store.
• Canned or shelf-stable pâté and meat spreads are safe to eat, but be sure to refrigerate them after opening the packages.
• Do not eat refrigerated smoked seafood. Canned or shelf-stable seafood, particularly when incorporated into a casserole, is safe to eat.
• Eat cut melon immediately. Refrigerate uneaten melon quickly if not eaten. Discard cut melon that is left at room temperature for more than 4 hours.

CASE Diagnosis made and prompt treatment initiated

The most likely diagnosis in this patient is listeriosis. Because the patient is moderately ill and experiencing uterine contractions, she should be hospitalized and monitored for progressive cervical dilation. Blood cultures should be obtained to identify L monocytogenes. In addition, an amniocentesis should be performed, and the amniotic fluid should be cultured for this microorganism. Stool culture and culture of the cerebrospinal fluid are not indicated. The patient should be treated with intravenous ampicillin, 2 g every 4 hours for 14 days. If she is allergic to penicillin, the alternative drug is trimethoprim-sulfamethoxazole, 8 to 10 mg/kg per day in 2 divided doses, for 14 days. Prompt and effective treatment of the mother should prevent infection in the fetus and newborn. ●