The Listeria monocytogenes infection during pregnancy, commonly called listeriosis, represents a serious maternal-fetal health concern that obstetricians must recognize and manage proactively. Although relatively rare, pregnant women bear a 10-20 times higher risk of contracting listeriosis than the general population, accounting for roughly one-quarter to one-third of all recorded infections. This heightened susceptibility is due to physiological and immunological changes in pregnancy that impact cell-mediated immunity, making early detection and treatment paramount for favorable maternal and neonatal outcomes.

Pathophysiology and Transmission

The Listeria monocytogenes is a Gram-positive intracellular bacterium primarily transmitted via the ingestion of contaminated food such as unpasteurized dairy products, deli meats, smoked seafood, and improperly cooked or stored foods. The pathogen’s ability to live and multiply within host cells allows it to evade some immune defenses and facilitates transplacental spread from mother to fetus. Vertical transmission can lead to devastating fetal complications including preterm birth, miscarriage, stillbirth, neonatal sepsis, and meningitis.

Clinical Presentation in Pregnancy

Maternal infection often presents nonspecifically, mimicking a mild flu-like illness with symptoms including fever, headache, myalgia, nausea, vomiting, and diarrhea. Approximately 20–30% of pregnant women with listeriosis may be asymptomatic, complicating timely diagnosis. The onset of symptoms can occur from days to several weeks after exposure, demanding high clinical suspicion especially in pregnant women presenting with febrile illness and compatible exposure history.

Diagnosis

The gold standard diagnostic test is blood culture, though sensitivity ranges from 36% to 55% in symptomatic pregnant women. Additional specimens for culture include amniotic fluid, placental tissue, cerebrospinal fluid, or neonatal blood if listeriosis is suspected post-delivery. Laboratory findings may also reveal leukocytosis and elevated inflammatory markers but are nonspecific. Given the common nonspecific symptomatology, detailed dietary and exposure history is critical for risk assessment.

Management

Once suspected or confirmed, management of listeriosis in pregnancy requires immediate initiation of appropriate antibiotics to reduce maternal morbidity and prevent fetal infection. The first-line treatment is high-dose intravenous ampicillin or amoxicillin, typically 6 grams per day divided every 6-12 hours, combined with gentamicin in severe cases. Treatment duration usually spans 14 days; however, it may extend based on clinical response and microbiological findings. An important clinical principle is initiating therapy promptly after obtaining blood cultures without waiting for results if clinical suspicion is strong.

Close fetal monitoring via ultrasound assessing fetal growth, amniotic fluid volume, and signs of distress is essential, as fetal infection can lead to preterm labor or demise. Termination of pregnancy may be considered in cases of severe maternal or fetal compromise, an option that requires multidisciplinary discussion.

Prevention

Prevention remains the cornerstone of protecting pregnant patients from listeriosis. Obstetricians should counsel patients rigorously on dietary precautions to avoid high-risk foods such as soft cheeses (e.g., Brie, Camembert), unpasteurized milk, refrigerated smoked seafood, deli meats unless heated until steaming, pâtés, and raw or undercooked meats. Safe food handling, proper refrigeration, and hand hygiene are critical adjuncts to dietary restrictions.

Patient education should emphasize awareness of symptoms warranting urgent medical evaluation, particularly fever or flu-like illness during pregnancy with relevant exposure history. Early presentation to healthcare facilitates prompt diagnosis and treatment, mitigating adverse outcomes.

Conclusion

Listeria infection during pregnancy is an uncommon but serious condition with significant risks to both mother and fetus. As obstetricians, maintaining vigilance through thorough history-taking, early diagnostic workup, timely antimicrobial therapy, and multidisciplinary fetal monitoring is essential. Active patient education on preventive measures plays a vital role in reducing listeriosis incidence. Ultimately, well-informed clinical management guided by current evidence ensures optimal pregnancy outcomes in the face of this potentially devastating infection.

Reference

• https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2014/12/management-of-pregnant-women-with-presumptive-exposure-to-listeria-monocytogenes
• https://firstexposure.ca/listeriosis-in-pregnancy-and-lactation/
• https://www.acog.org/womens-health/faqs/listeria-and-pregnancy
• https://pmc.ncbi.nlm.nih.gov/articles/PMC2621056/
• https://www.obgproject.com/2023/06/14/acog-guidance-pregnancy-and-listeria-exposure/
• https://www.sahealth.sa.gov.au/wps/wcm/connect/40111d804ee4eb738f438fd150ce4f37/Listeria+in+pregnancy_Clinical+Guideline_Dec14.pdf?MOD=AJPERES
• https://www.fda.gov/food/health-educators/listeria-food-safety-moms-be
• https://pmc.ncbi.nlm.nih.gov/articles/PMC8165209/
• https://healthify.nz/health-a-z/l/listeria-and-pregnancy
• https://www.foodauthority.nsw.gov.au/sites/default/files/_Documents/foodsafetyandyou/listeria_and_pregnancy.pdf