Listeria Annual Summary, 2019

Listeria Initiative Data

We report confirmed and probable cases of listeriosis according to the Listeriosis 2019 case definition. In brief, confirmed cases occur in persons with laboratory confirmation by culture of Listeria monocytogenes from a normally sterile site (e.g., blood or cerebrospinal fluid) or from products of conception (e.g., amniotic fluid, placental or fetal tissue). Probable cases occur in persons with presumptive (culture-independent diagnostic test [CIDT]) laboratory evidence of Listeria monocytogenes from a normally sterile site or from products of conception or in a mother or neonate who met only an epidemiologic linkage criterion. Thus, in a mother-infant pair in which one has a confirmed case, the other will be either a confirmed or probable case. In the remainder of this report, we call these illnesses simply listeriosis.

For cases in which L. monocytogenes is isolated from multiple anatomical sites, the case is considered to be invasive if any isolate was obtained from a normally sterile site or from products of conception. For cases in which L. monocytogenes was isolated from multiple normally sterile anatomical sites, the annual summary reports the most invasive site, using a hierarchy (in descending order of invasiveness: cerebrospinal fluid bone or joint fluid, blood, other sterile site, and products of conception).

Each mother-infant pair in episodes of pregnancy-associated listeriosis is reported as a single report, even when isolates are obtained from both the mother and the infant. The rationale is that an episode of pregnancy-associated listeriosis inherently involves both the mother and the infant, because the infant's infection, in most cases, occurs because the mother ate contaminated food. Reports are classified as pregnancy-associated if illness occurred in a pregnant person or infant ≤28 days old; all other cases are considered to not be associated with pregnancy.

Cases reported to the Listeria Initiative

• 46 states submitted 792 listeriosis case reports with information about patients in 2019.
  
• 765 (97%) reports included one or more patients with listeriosis; these are included in the remainder of the report.
  
  • 667 (87%) reports were not associated with pregnancy
  • 98 (13%) reports were pregnancy-associated.
• 17 (2%) reports were for patients with suspected listeriosis, i.e., with isolation from a non-invasive specimen.
  • Of these, 16 were not associated with pregnancy-associated and 1 was pregnancy-associated.
  • These cases were excluded from further analyses.
• 9 (1%) reports did not have enough data to categorize illness as confirmed, probable, or suspected.
  • All these cases were not associated with pregnancy.
  • These cases were excluded from further analyses.

Jurisdictions reporting at least one listeriosis case to the Listeria Initiative during 2019 are shown in Figure 1.

Figure 1: Number of reports submitted to the Listeria Initiative, by jurisdiction, 2019 (n=765). ^*,†

_{* Number of cases reported to the Listeria Initiative in 2019 are indicated on each jurisdiction that reported.}

_{† All states reported to both the Listeria Initiative (LI) and NNDSS apart from the following: Only LI: Alaska and New Mexico; Neither LI nor NNDSS: Montana, North Dakota, South Dakota, Wyoming, and Washington, D.C.}

Listeriosis not associated with pregnancy

Demographic and clinical characteristics of 667 patients with listeriosis not associated with pregnancy are shown in Table 1.

Highlights

• The median age of patients was 71 years.
• Most isolates were from blood (81%) or cerebrospinal fluid (15%).
• 91% of patients were hospitalized.
• 18% of patients died.

Table 1. Demographic and clinical characteristics of patients with listeriosis not associated with pregnancy reported to the Listeria Initiative, 2019 (n=667).

_{* Missing and unknown information was excluded from the denominator for each characteristic: age (n=6), ethnicity (n=76), race and ethnicity (n=98).}

_{‡ Race and ethnicity categories with no cases are not listed.}

_{¶ Peritoneal fluid (13), pleural fluid (7), bone or joint fluid (3), eye, (1), aortic tissue (1).}

Highlight

• The number of patients in each 10-year group increased with age for each older age group among those aged 50–79 years.

Figure 2. Patients with listeriosis not associated with pregnancy, by age group and sex, Listeria Initiative, 2019 (n=662*).

_{* Only patients who had information on both sex and age are included in this figure.}

Pregnancy-associated listeriosis

Demographic and clinical characteristics of the 98 pregnancy-associated listeriosis patients are shown in Table 2. All pregnant persons were women.

Highlights

• Among the 98 pregnancies, there were 47 cases in mothers and 51 cases in infants.
  • 51 had Listeria detected only in the infant
  • 37 had Listeria detected only in the mother
  • 10 pregnancies had Listeria detected in both the mother and the infant
• 39% of pregnancies included a woman of Hispanic ethnicity.
• 20% of pregnancies included a fetal death.
• 6% of pregnancies reported a live-born infant death.

Table 2. Demographic and clinical characteristics of episodes of pregnancy-associated listeriosis reported to the Listeria Initiative, 2019 (n=98 pregnancies).*

_{* Mother-infant pairs are counted as a single case.}

_{¶ Missing and unknown information was excluded from the denominator for each characteristic: age (n=6), ethnicity (n=8), race and ethnicity (n=8).}

_{§ For cases in which L. monocytogenes was isolated from multiple normally sterile anatomical sites, the annual summary reports the most invasive site, using a hierarchy (in descending order of invasiveness: cerebrospinal fluid, bone or joint fluid, blood, other sterile site, and product of conception).}

_{‡ Products of conception included placenta (n=14), amniotic fluid (n=1), umbilical cord blood (n =1).}

_{† Hospitalization related to Listeria infection.}

Listeria outbreak investigations

The Listeria Initiative was designed to expedite investigation of and response to clusters and outbreaks. (A cluster is defined as 2 or more persons whose isolates are closely genetically related; clusters that were linked to a common source are called outbreaks.) By participating in the Listeria Initiative, including use of the standard questionnaire, state and local health departments contribute data on food exposures that can be used for rapid investigation of clusters and for other epidemiological analyses.

During 2019, state and local health officials, regulatory agencies, and CDC identified 31 clusters of listeriosis.

More information on Listeria outbreaks can be found in CDC's BEAM Dashboard and in CDC's list of multistate foodborne outbreaks.

Reporting statistics

Prompt interviewing of all patients with listeriosis, timely submission of Listeria Initiative standardized questionnaires to CDC, rapid subtyping by whole-genome sequencing, and uploading of sequencing results to PulseNet allow for rapid detection and investigation of listeriosis clusters.

To help meet these objectives, reporting statistics and goals for the Listeria Initiative (below) were proposed at the 2012 Council of State and Territorial Epidemiologists (CSTE) Annual Meeting. CDC sends state-specific summaries to state epidemiologists. Health department personnel may also request their state's reporting statistics by emailing edebresponse@cdc.gov and listeria@cdc.gov.

Table 3. National listeriosis surveillance metrics by year, Listeria Initiative, 2015–2019

Table 4. Proposed national listeriosis reporting goals for 2016 and Listeria Initiative metrics for 2019.*

_{* Among 46 districts, not including District of Columbia in 2019.}

_{† For pregnancy-associated case reports, 1 case report includes a mother-infant pair. Details of this definition can be found here.}

_{‡ Calculated among 931 NNDSS case reports in 2019.}

_{§ Calculated among 749 case reports to PulseNet in 2019.}

_{¶ Calculated among cases reports with LI questionnaire submitted.}

_{** Calculated for isolates that are reported to PulseNet with information on submission dates.}

_{†† Calculated for LI case reports.}

_{‡‡ Calculated for LI case reports; information on consumption history for turkey breast, blue cheese, coleslaw, smoked fish, and yogurt.}

Other sources of surveillance data

NNDSS data

The National Notifiable Disease Surveillance System (NNDSS) collects and compiles reports of nationally notifiable infectious diseases, including listeriosis.

FDOSS outbreak data

The Foodborne Disease Outbreak Surveillance System (FDOSS) collects reports of foodborne disease outbreaks from local, state, tribal, and territorial public health agencies.

Recommended citation

Centers for Disease Control and Prevention (CDC). National Listeria surveillance annual summary for 2019. Atlanta, Georgia: US Department of Health and Human Services, CDC, 2023.