Neonatal listeriosis is a (typically) transplacentally contracted disease caused by the presence of the Gram-positive motile rods, facultative intracellular, foodborne pathogen known as Listeria monocytogenes. The patient population especially susceptible to listeriosis includes the elderly, the immunosuppressed, and those who are pregnant. It is important to note that L. monocytogenes is ever present in nature as it in is found in the faecal flora of many mammals and is a common foodborne illness. Possible contaminated food sources include unpasteurized dairy products, soft cheeses, raw vegetables, prepared deli meats and salads, refrigerated meat spreads, and smoked seafood.
In the United States, there have been reported incidents of food product recalls due to the concerns of listerial contamination thanks to routine screening and surveillance. Despite of this strict surveillance, sporadic outbreaks of listerial food poisoning have been seen in the community.
As the typical mode of transmission of Listeria to neonates is via a pregnant person, it is essential to be aware of symptoms and signs present in the expecting mother as well as the neonate. Listeriosis is 18 times more common in pregnant individuals than in the nonpregnant population. Listerial infections in pregnant patients account for up to 25% of all listerial infections.
In pregnant individuals, a listeriosis infection is most likely to be contracted within the third trimester, with increased chance of fetal death the later it is into the pregnancy. It is possible for the organism to spread across the placenta, for aspiration of infected amniotic fluid, or for ascending infection from the vaginal flora. Though the indicators of listeriosis in pregnant patients are rather unspecific (or sometimes even absent), they include backache, sore throat, flu-like symptoms, or gastroenteritis.
Neonatal listeriosis has 2 different types of clinical presentations in the neonates, namely early- and late-onset disease.
Early-onset neonatal listeriosis is usually acquired by transplacental transmission or aspiration of infected amniotic fluid. Symptoms of this clinical disease present within 5 days of the birth (mean age of 36 hours). Neonates are usually preterm, associated with chorioamnionitis. Septicemia (80%), respiratory distress or pneumonia (40%), and meningitis (25%) are typical clinical manifestations in neonates. Granulomatosis infantisepticum, presenting as diffuse erythematous rash with small granulomatous nodules, is a pathognomonic feature of early-onset listeriosis. There is 20%-40% mortality rate in early-onset neonatal listeriosis.
In contrast, late-onset neonatal listeriosis is thought to occur during delivery through the birth canal or nosocomial contamination. It typically begins after 5 days postpartum (mean age of 2 weeks). Affected neonates are typically born at term, and they present with septicemia and meningitis. However, the mortality rate is lower (0%-20%).
Listeriosis can be confused with many other infectious diseases that result in the nonspecific symptoms of fever and other constitutional symptoms. In coming to a diagnosis, one must rule out these other potential diagnoses, typically through a culture of the organism from the cerebrospinal fluid or blood. Some infections that should be ruled out include:
Early-onset neonatal listeriosis:
Group B strep and Gram-negative enteric organisms (predominantly E. coli)
Gram-negative enteric bacilli, such as Klebsiella
Gram-positive organisms, such as Enterococcus (Enterococcus faecalis, E. faecium)