The motivation behind this article stems from our desire to enhance awareness and strategies for the prevention and eradication of LM infection during the perinatal period. This issue, although critical, remains insufficiently acknowledged as a public health concern, endangering the well-being of pregnant individuals and newborns. Notably, the prevalence of LM infection exhibits significant variation globally, with higher incidence rates observed in certain developing regions and an uptrend in developed nations[7]. As a major city in the southeast of China (Xiamen), the incidence of pregnancy-associated listeriosis is 7.15/100,000 deliveries, between Xi'an (a city in the northwest) and Beijing (a city in the north) in China[3, 8], but higher than some European countries[7, 9, 10]. Pregnancy-associated listeriosis is sporadic, mainly concentrated in spring and summer, consistent with previous studies[8, 11]. The mortality rate of offspring with pregnancy-associated listeriosis in this study was 70.0%, higher than the 32.7%~57.1% reported in two recent systematic reviews in China[12, 13]. Infections contracted during the first trimester present the gravest outcomes, with a mortality rate of 100%, whereas third-trimester infections show a reduced mortality rate of 57.1%. Nevertheless, the prognosis for pregnant women remains positive, in line with other research findings[3, 10, 12, 14].
Listeriosis is primarily contracted through the consumption of foods contaminated with LM, a bacterium capable of surviving under various conditions, including refrigeration. It can be transmitted to humans through ingestion of contaminated food, such as improperly heated meat, unpasteurized dairy products, raw or improperly cleaned vegetables and fruits[15]. Currently, China does not have dietary guidelines for preventing LM infection. Therefore, strengthening education on food safety awareness among pregnant women can promote prevention[3]. Pregnant women are more susceptible and more severe after infection due to changes in their immune system during pregnancy, which may be attributed to pregnancy induced maternal T-cell suppression, as well as LM and their various virulence factors to facilitate entry into host cells and escape intracellular degradation by the host immune system[1, 14, 16, 17]. The placenta plays an essential role in protecting the fetus from external stimuli. However, once bacteria invade the villous space, the placenta may become a lesion that leads to repeated maternal infections[16]. In healthy individuals, LM infection is usually limited to mild gastrointestinal symptoms. Pregnant patients infected with LM exhibit symptoms ranging from mild respiratory symptoms to mild gastrointestinal symptoms, resembling influenza or even being asymptomatic[14]. In this study, The predominant symptoms observed in pregnant women were fever, with a body temperature between 38 ℃ and 40 ℃, followed by abdominal pain, reduced fetal movement, and fetal tachycardia. The laboratory test results showed elevated levels of NE%, CRT, and PCT in all pregnant women. Nevertheless, these symptoms and laboratory findings lack distinctive characteristics, therefore the diagnosis of LM infection mainly relies on nucleic acid testing or microbial culture[14]. In addition, histopathological evaluation of the placenta also plays an important role[1, 14]. For example, in our study, all placental histopathological examinations showed varying degrees of acute chorioamnionitis (Grade II-III) and micro-abscess formation in patients.
Currently, high-dose penicillin or ampicillin is the preferred treatment for LM infection, while meropenem or SXT can be used for patients allergic to penicillin[18–20]. The general duration of antibiotic treatment is 2 weeks from the onset of the disease to delivery of the fetus, in severe cases, the application time of antibiotics can be appropriately extended[15]. Newborns born to mothers with LM should be followed up for 2–3 months after delivery[14]. Our study revealed that as cephalosporin antibiotics are the preferred empirical treatment for non-specific obstetric infections in China, 44.4% (4/9) of pregnant women initially received treatment with cephalosporin antibiotics. However, Antimicrobial susceptibility test showed that the isolated strains of LM were resistance to cephalosporin antibiotics, which may result in a higher mortality rates for offspring of patients with pregnancy-associated listeriosis[8]. Meanwhile, the isolated strains have shown susceptible to penicillin, ampicillin, meropenem, and erythromycin, with low MIC values for levofloxacin, vancomycin, tetracycline, gentamicin, and linezolid (Table 4). The rarity of LM infections and the limited strain exposure to antibiotics may be reasons why LM exhibits high susceptible to these antibiotics[20, 21].
In conclusion, while pregnancy-associated listeriosis remains a rarity in Xiamen, it is imperative for clinicians to prioritize food safety education for pregnant women to prevent infection. Due to the rarity and non-specific clinical features of LM infection, early identification of pregnancy-associated listeriosis poses a challenge. When there is suspicion of LM infection in pregnant women, samples should be actively sent for microbiological culture and placental tissue pathology testing, while considering appropriate antimicrobial therapy[1].