Listeria Monocytogenes Infection

Introduction
Clinical Manifestations
Investigation
Treatment

Introduction

Listeria Monocytogenes is a short Gram-positive rod. Transmission to humans occurs via food, especially dairy products contaminated by infected farm animals. In United States, occurrence rates are 13/100,000 live births. It is less common in Australia. The mortality of neonatal listeriosis is about 5-15%.

This infection is classified as a notifable disease.

Clinical Manifestations

Transplacental infection

Causes a non-specific influenzal or gastroenteritic illness in pregnant women, during which the organism may infect the fetus either by spread across placenta or through amniotic fluid. First and second trimester infection may cause fetal death. Later in pregnancy infection may precipitate preterm labour with foetal distress and meconium staining of the liquor. Since meconium staining of the liquor is rare below 34 weeks, its presence should raise suspicion of listeriosis.

Characteristically, small (2-3mm) pinkish-grey cutaneous granulomas are present and, at autopsy, similar small granulomatous lesions are widespread in the liver, lungs, CNS and many other tissues and organs.

Early-onset infection

60% of infants infected intrapartum are preterm and become ill within 24 hours of birth. Most have disseminated infection with pneumonia, meningitis, thrombocytopenia, anaemia and sometimes conjunctivitis. Both blood and stool should be cultured. Most cases are sporadic, but epidemics are described.

Late-onset infection

Usually presents as meningitis, probably due to nosocomial infection. Median age of onset is about 2 weeks.

Investigation

Gram stain can be variable and the organism slow growing.

Treatment

Penicillin or ampicillin and gentamicin.

Listeria is resistant to all third generation cephalosporins.

References

Feigh, R. D., and Cherry, J. D. Textbook of pediatric Infectious Diseases (3^rd Ed.). Philadelphia: Saunders, 1992.

Stoll, B. J.Weisman, L.E. Infections in perinatology. Clin. Perinatol. 24:1, 1997.

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