Epidemiology

Although Listeria is widespread in nature and the ingestion of L monocytogenes is relatively common, the annual incidence of listeriosis among humans is low.[10] Most cases are sporadic and are reported in high-income countries; the fatality rate may be high.[11][12][13][14][15] Incidence data in low-income countries are generally not available.[16]Listeria can be isolated from the stools of up to 5% of healthy adults, and disease may be transmitted from this population.[17]

Immunocompetent patients rarely develop disseminated disease, although they may develop a gastroenteritis syndrome. The pathogen has a predilection for neonates (age <1 month), adults (especially >50 years), pregnant women (30% of all patients), and immunocompromised people (with HIV/AIDS, cancer, haematological malignancies, those undergoing corticosteroid treatment, or transplant recipients).[1][18][19] Impaired cellular immunity is associated with increased incidence of the disease.

Microbiological and epidemiological data on 1,933 patients with listeriosis reported in England and Wales from 1990 to 2004 indicates a substantial increase in incidence occurring from 2001 to 2004. The reasons for the increase are not known, but incidence was sporadic and predominantly in patients 60 years of age or older with bacteraemia.[20]

In the US, laboratory-confirmed listeriosis incidence is 0.24 cases per 100,000, and the rate of pregnancy-associated listeriosis is 13 times higher than that for the general population.[21][22] Intensive monitoring and recall of potentially contaminated products has decreased the prevalence of perinatal listeriosis by 44% in the US.[17]

The relative risk in the US of invasive listeriosis is significantly higher for Hispanic people than for non-Hispanic people, both in the general population and also in pregnant women.[23] Among Hispanic women, the crude incidence of pregnancy-associated listeriosis increased from 5.09 per 100,000 in 2004 to 2006 to 12.37 per 100,000 in 2007 to 2009.[24] Pregnancy-associated listeriosis among non-Hispanic women showed a much lower crude incidence increase for the same periods.

In Australia, from January to April 2018, an outbreak of listeriosis was reported.[25] All patients were hospitalised. Epidemiological investigation found that the source of the outbreak was rockmelon (cantaloupe melons) from a single grower.[25]

In 2018, the European Centre for Disease Control reported an outbreak of invasive L monocytogenes infections (confirmed by whole-genome sequencing) linked to frozen corn, and possibly to other frozen vegetables, in the UK and 4 EU member states (Austria, Denmark, Finland, Sweden). There have been 47 cases reported since 2015 and, as of June 2018, 9 patients have died due to or with the infection.[21]

In 2017, 2,502 confirmed cases of listeriosis were reported by 30 EU/EEA countries, with an age-standardised notification rate of 0.42 per 100 000 population.[26] In 2019, there were 222 confirmed cases of L monocytogenes infection linked to chilled pork in Spain; 3 fatalities and 6 miscarriages were reported.

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