By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

Dr. Deresinski reports no financial relationships relevant to this field of study.

SYNOPSIS: Infection with Listeria monocytogenes in pregnancy is associated with frequent fetal loss. In others, bacteremia and central nervous system infections are associated with significant mortality.

SOURCE: Charlier C, Perrodeau É, Leclercq A, et al. Clinical features and prognostic factors of listeriosis: The MONALISA national prospective cohort study. Lancet Infect Dis 2017 Jan 28. pii: S1473-3099(16)30521-7. doi:10.1016/S1473-3099(16)30521-7. [Epub ahead of print].

Charleir and colleagues prospectively collected data on almost all patients with Listeria monocytogenes infection in France during almost four years ending in 2013. Of the 818 patients included in their analysis, 427 had bacteremia, 252 had neurolisteriosis, and 107 had maternal-fetal infection, while the remaining 32 had other forms of infection.

One-third of the 107 women with maternal-fetal infection were from the Maghreb or the Sahel. While the infection usually is symptomatic, the six mothers with late onset listeriosis had normal examinations throughout their pregnancy and delivery. Maternal blood cultures were positive in 47 (55%) of 85 cases, while cultures were positive in 50 (78%) of 64 placental samples and 52 (78) of 67 gastric fluid samples. All pregnant women recovered, including 10 who did not receive antibiotics. Major adverse effects occurred in 89 (83%) cases, including fetal death and premature delivery at < 32 weeks of gestation. Fetal loss occurred in 26 (24%), with all at < 26 weeks gestation.

Of the 252 patients with neurolisteriosis, 87% had encephalitis, while the remaining 13 had meningitis alone. Only 42 (17%) had evidence of brainstem involvement and six (2%) had brain abscesses. Cerebrospinal fluid (CSF) was abnormal in all 235 in whom it was examined, with median values of nucleated cells, polymorphonuclear leukocytes, and protein of 457/mm3, 65%, and 2.1 g/L. The median CSF blood:glucose ratio was 0.31. Only 39% of patients with central nervous system infection survived without neurological impairment.

Bacteremia was associated with significantly higher three-month mortality than was central nervous system infection. Among the independent risk factors for mortality in both bacteremia and neurolisteriosis cases were cancer, pre-existing organ dysfunction, development of multiorgan failure, and monocytopenia. Patients with neurolisteriosis who were bacteremic had higher mortality than those in whom bacteremia was not detected. Among patients with neurolisteriosis, mortality was three times higher in those with encephalitis than those without it. Mortality was higher in patients with central nervous system infection who received dexamethasone. The best outcomes were associated with treatment with an “anti-listeria” ß-lactam (penicillin G, amoxicillin, ticarcillin, piperacillin, imipenem, or meropenem), especially when given with gentamicin. Trimethoprim-sulfamethoxazole also was effective.

An interesting finding was that while CRP was elevated in 96% of the 627 tested, procalcitonin was increased in only 66% of the 186 tested.

COMMENTARY

Listeria monocytogenes is an aerobic and facultatively anaerobic, ß-hemolytic, non–spore-forming, short, gram-positive rod with characteristic tumbling motility. On Gram stain, it may be confused with other bacteria, particularly diphtheroids. Among the risk factors for infection are age (neonates and elderly), malignancy, immunosuppressive therapy, alcoholism, diabetes mellitus, chronic liver or renal disease, and iron overload. The incidence of Listeria infection per 100,000 population has been reported to be 0.29 overall, 1.3 in individuals 65 years of age, and 3.0 in pregnant women.

Penicillins and carbapenems are active against L. monocytogenes, while cephalosporins are not. The generally recommended treatment is a penicillin with, especially for meningitis, gentamicin, although trimethoprim-sulfamethoxazole alone is also effective. The study reviewed here identified dexamethasone administration as associated with reduced survival.

While encountered infrequently by most clinicians in the United States, it is critical that listeriosis be considered as the cause of febrile illness and, especially, meningitis and encephalitis.