Where is listeriosis most commonly found?

Epidemiology

Listeria monocytogenes is widespread in nature, has been isolated throughout the environment, and is associated with epizootic disease and asymptomatic carriage in >42 species of wild and domestic animals and 22 avian species. Epizootic disease in large animals [e.g., sheep, cattle] is associated with abortion and circling disease, a form of basilar meningitis.L. monocytogenes is isolated from sewage, silage, and soil, where it survives for >295 days. Human-to-human transmission rarely occurs except in maternal-fetal transmission. The annual incidence of listeriosis decreased by 36% between 1996 and 2004 and has remained level since then. However, food-borne outbreaks continue to occur. In 2011, 84 cases and 15 deaths in 19 states were traced to cantaloupes from a single source. The cases were connected by use of pulsed-field gel electrophoresis, which showed that 4 different strains traced to the same source. The rate ofListeria infections varies among states. Epidemic human listeriosis has been associated with food-borne transmission in several large outbreaks, especially in association with aged soft cheeses; improperly pasteurized milk and milk products; contaminated raw and ready-to-eat beef, pork, and poultry, and packaged meats and salads; and vegetables both fresh and frozen harvested from farms where the ground is contaminated with the feces of colonized animals. Food-borne outbreaks in 2016 included raw milk, packaged salads, and frozen vegetables. The ability ofL. monocytogenes to grow at temperatures as low as 4°C [39.2°F] increases the risk for transmission from aged soft cheeses and stored contaminated food. Listeriosis is an uncommon but important recognized etiology of neonatal sepsis and meningitis. Small clusters of nosocomial person-to-person transmission have occurred in hospital nurseries and obstetric suites. Sporadic endemic listeriosis is less well characterized. Likely routes include food-borne infection and zoonotic spread.Zoonotic transmission with cutaneous infections occurs in veterinarians and farmers who handle sick animals.

Reported cases of listeriosis are clustered at the extremes of age. Some studies show higher rates in males and a seasonal predominance in the late summer and fall in the Northern hemisphere. Outside the newborn period and during pregnancy, disease is usually reported in patients with underlying immunosuppression, with a 100-300 times increased risk in HIV-infected persons and in the elderly population [Table 215.1]. In a recent surveillance study from England, malignancies accounted for one third of cases, with special risk associated with cancer in elderly persons.

The incubation period, which is defined only for common-source food-borne disease, is 21-30 days but in some cases may be longer. Asymptomatic carriage and fecal excretion are reported in 15% of healthy persons and 5% of abattoir workers, but duration of excretion, when studied, is short [50 years].

Acute gastroenteritis is an unusual manifestation of listeriosis, despite its transmission by food, but it has been reported in point‐source outbreaks. It is accompanied by fever and abdominal pain, and it has an incubation period of about 1 day.