Listeriosis

Reporting Information

Class B

Report a case, suspected case, and/or positive laboratory result to the local public health department in which the patient resides by the close of the next business day. If patient residence is unknown, report to the local public health department in which the reporting healthcare provider or laboratory is located.

Reporting Form(s) and/or Mechanism

The Ohio Disease Reporting System (ODRS) should be used to report cases and lab findings to the Ohio Department of Health (ODH). For healthcare providers without access to ODRS, the Ohio Confidential Reportable Disease Form (HEA 3334) may be used.

The Positive Laboratory Findings for Reportable Disease Form (HEA 3333) may be used for laboratories without access to ODRS or electronic laboratory reporting (ELR) to report positive results.

The Listeria Initiative Case Report Form (CDC OMB 0920-0728) is required for completion by the local public health department when following up with cases. A Spanish version of this form is available. Information collected from the form should be entered into ODRS where fields are available, and the form should be uploaded in the Administration section of ODRS. If the case is lost to follow up, pages 3-5 of the form should be uploaded to ODRS. If you have problems uploading the form, you may fax the completed form to the ODH Bureau of Infectious Diseases (BID) at (614) 564-2456.

Key Fields for ODRS Reporting

  • Date of illness onset.
  • Interview fields.
  • All fields in the Food History module.
  • All fields in the Travel and Other Exposures module.

Agent

Listeria monocytogenes, is a Gram-positive rod-shaped bacterium and is the only Listeria species consistently associated with human illness. Twelve serotypes of L. monocytogenes can cause disease, but more than 95% of human isolates belong to only three serotypes: 1/2a, 1/2b, and 4b. L. monocytogenes serotype 4b is responsible for sporadic human cases worldwide and major foodborne outbreaks in Europe and North America since the 1980s.

L. monocytogenes resists heat, salt, nitrite, and acidity better than many organisms and grows at temperatures as low as 34°F (1°C). Low storage temperatures slow, but do not stop, growth. Commercial freezer temperatures of 0°F will stop L. monocytogenes from multiplying, but may not destroy it. Commercial pasteurization procedures for dairy products have been determined to be sufficient to destroy this organism. Proper cooking and reheating of foods will effectively control Listeria. The organism can colonize cracks, food-filled crevices, and inaccessible areas in food preparation and processing facilities and equipment. This presents a significant challenge to sanitation procedures.

Infectious Dose

The infectious dose is unknown, but it is believed to be strain and host dependent. In susceptible persons, the infectious dose may be less than 1,000 organisms.

Case Definition

Clinical Criteria

Invasive Listeriosis

  • Systemic illness caused by L. monocytogenes manifests most commonly as bacteremia or central nervous system infection. Other manifestations can include pneumonia, peritonitis, endocarditis, and focal infections of joints and bones.
  • Pregnancy-associated listeriosis has generally been classified as illness occurring in a pregnant woman or in an infant age ≤28 days. Listeriosis may result in pregnancy loss (fetal loss before 20 weeks gestation), intrauterine fetal demise (≥20 weeks gestation), pre-term labor, or neonatal infection, while causing minimal or no systemic symptoms in the mother. Pregnancy loss and intrauterine fetal demise are considered to be maternal outcomes.
  • Neonatal listeriosis commonly manifests as bacteremia, central nervous system infection, and pneumonia and is associated with high fatality rates. Transmission of Listeria from mother to baby transplacentally or during delivery is almost always the source of early-onset neonatal infections (diagnosed between birth and 6 days) and the most likely source of late-onset neonatal listeriosis (diagnosed between 7 and 28 days).

Non-Invasive Listeria Infections

  • Listeria infection manifesting as an isolate from a non-invasive clinical specimen suggestive of a non-invasive infection; includes febrile gastroenteritis, urinary tract infection, and wound infection.

Laboratory Criteria for Diagnosis

Confirmatory Laboratory Evidence

  • Isolation of L. monocytogenes from a specimen collected from a normally sterile site reflective of an invasive infection (e.g., blood or cerebrospinal fluid or, less commonly: pleural, peritoneal, pericardial, hepatobiliary, or vitreous fluid; orthopedic site such as bone, bone marrow, or joint; or other sterile sites including organs such as spleen, liver, and heart, but not sources such as urine, stool, or external wounds) OR
  • For maternal isolates: In the setting of pregnancy, pregnancy loss, intrauterine fetal demise, or birth, isolation of L. monocytogenes from products of conception (e.g., chorionic villi, placenta, fetal tissue, umbilical cord blood, amniotic fluid) collected at the time of delivery OR
  • For neonatal isolates: In the setting of live birth, isolation of L. monocytogenes from a non-sterile neonatal specimen (e.g., meconium, tracheal aspirate, but not products of conception) collected within 48 hours of delivery.

Presumptive Laboratory Evidence

  • Detection of L. monocytogenes by culture-independent diagnostic testing (CIDT) in a specimen collected from a normally sterile site (e.g., blood or cerebrospinal fluid or, less commonly: pleural, peritoneal, pericardial, hepatobiliary, or vitreous fluid; orthopedic site such as bone, bone marrow, or joint; or other sterile sites including organs such as spleen, liver, and heart, but not sources such as urine, stool, or external wounds) OR
  • For maternal isolates: In the setting of pregnancy, pregnancy loss, intrauterine fetal demise, or birth, detection of L. monocytogenes by CIDT from products of conception (e.g., chorionic villi, placenta, fetal tissue, umbilical cord blood, amniotic fluid) collected at the time of delivery OR
  • For neonatal isolates: In the setting of live birth, detection of L. monocytogenes by CIDT from a non-sterile neonatal specimen (e.g., meconium, tracheal aspirate, but not products of conception) collected within 48 hours of delivery.

Supportive Laboratory Evidence

  • Isolation of L. monocytogenes from a non-invasive clinical specimen, e.g., stool, urine, wound, other than those specified under maternal and neonatal specimens in the confirmatory laboratory evidence section.

Epidemiologic Linkage

For probable maternal cases:

  • A mother who does not meet the confirmed case criteria, BUT
  • Who gave birth to a neonate who meets confirmatory or presumptive laboratory evidence for diagnosis, AND
  • Neonatal specimen was collected up to 28 days of birth.

For probable neonatal cases:

  • Neonate(s) who do not meet the confirmed case criteria AND
    • Whose mother meets confirmatory or presumptive laboratory evidence for diagnosis from products of conception, OR
    • A clinically compatible neonate whose mother meets confirmatory or presumptive laboratory evidence for diagnosis from a normally sterile site.

Case Classification

Suspected

A person with supportive laboratory evidence.

Probable

  • A person who meets presumptive laboratory evidence OR
  • A mother or neonate who meets the epidemiologic linkage but who does not have confirmatory laboratory evidence.

Confirmed

A person who meets confirmatory laboratory evidence.

Not a Case

This status will not generally be used when reporting a case, but may be used to reclassify a report if investigation revealed it was not a case.

Criteria to Distinguish a New Case from an Existing Case

There is currently insufficient data available to support a routine recommendation for criteria to distinguish a new case of listeriosis from prior reports or notifications. Duplicate or recurring reports of listeriosis in an individual should be evaluated on a case-by-case basis.

Comments

Pregnancy loss and intrauterine fetal demise are considered maternal outcomes and would be counted as a single case in the mother. Cases in neonates and mothers should be reported separately when each meets the case definition. A case in a neonate is counted if live born.

Signs and Symptoms

Listeriosis is typically a foodborne bacterial disease (though fetal and neonatal infection can be acquired transplacentally or during delivery) and may present as one of two clinical pictures:

Invasive Listeriosis

L. monocytogenes can spread to the blood and penetrate the blood-brain-barrier causing septicemia or meningitis. Bacteria can also penetrate the placental barrier leading to severe infections of the fetus. Those at high risk for invasive listeriosis, include people who are immunocompromised, older adults ≥65 years of age, pregnant women, and the very young. The incubation period is variable and ranges from 3 to 70 days. The median incubation period is longer among pregnant women (2-4 weeks) than non-pregnant individuals (1 to 14 days). Clinical presentation depends on the organ system(s) affected and may include:

  • Meningitis.
  • Pneumonia.
  • Septicemia.
  • Endocarditis.
  • Abscesses, skin lesions, conjunctivitis (milder forms).

In pregnant women, listeriosis is particularly harmful. Infected pregnant women may experience mild flu-like symptoms, although they are at risk for:

  • Premature delivery.
  • Miscarriage (i.e., spontaneous abortion).
  • Stillbirth.

In infants, symptoms may include:

  • Loss of appetite.
  • Lethargy.
  • Jaundice.
  • Vomiting.
  • Respiratory distress (usually pneumonia).
  • Skin rash.
  • Shock.
  • Meningitis.
  • Death within a few hours of birth.

Non-invasive Listeriosis

A milder form of the disease is also referred to as acute febrile gastroenteritis, which typically resolves in 2-3 days. After an incubation period of 24 hours, symptoms following ingestion of high doses of L. monocytogenes can occur in healthy individuals and may include:

  • Diarrhea.
  • Fever.
  • Headache.
  • Myalgia (muscle pain).

Diagnosis

Listeria can be cultured from blood, cerebrospinal fluid, or other normally sterile locations. Listeria can also be cultured from specimens such as meconium, placental or fetal tissue, or amniotic fluid. Fecal culture is not sensitive or specific; 1-5% of the population may carry L. monocytogenes asymptomatically in the intestines. Serologic tests also have poor sensitivity and specificity.

Laboratories should send all Listeria isolates to ODH Laboratory for serotyping and molecular analysis. For specimens and isolates being sent to ODH Laboratory for further testing, the Ohio Department of Health (ODH) Laboratory Microbiology Specimen Submission Form (HEA 2530) is required.

Detection of L. monocytogenes in a food source supports the diagnosis. Food samples being sent to ODH Laboratory for testing need to have the Ohio Department of Health (ODH) Laboratory Food Sample Submission Form (HEA FOOD) accompanying the sample.

Epidemiology

Source

Listeria are found widely in the environment and in animals. They have been isolated from soil, dust, animal feed, water, sewage, domestic and wild mammalian and avian species, fish, crustaceans, and asymptomatic humans.

Foods associated with common source outbreaks include raw and contaminated pasteurized milk, soft cheeses, cole slaw, and celery. Uncooked hot dogs, ready-to-eat meats, undercooked chicken, and unwashed vegetables have also been associated with listeriosis.

Occurrence

Approximately 1-5% of the population is thought to carry L. monocytogenes asymptomatically in the intestines. Healthy people rarely become ill after exposure. Incidence in humans is higher in the summer.

Severe disease is most likely to occur in older adults, persons with weakened immune systems, pregnant women, and neonates. L. monocytogenes can cause community-acquired meningitis. The mortality rate of invasive disease is 15-20%, with higher rates among older adults and the immunocompromised, including neonates.

Although pregnant women rarely become ill or die, listeriosis may result in the death of the fetus or neonate. Combined perinatal and neonatal mortality rates from 14-56% have been reported. The case fatality rate is approximately 25% in infected newborns.

In the United States, an estimated 1,600 persons become ill with listeriosis each year. About one in five people with listeriosis dies.

In Ohio, the annual incidence of listeriosis cases is between 0.2 and 0.3 cases per 100,000 population. More than 80% of these cases occurred in individuals over 60 years of age.

Mode of Transmission

Although Listeria can be spread by inhalation or direct contact (e.g., genital contact), most infections are acquired by ingestion. Contaminated food sources include raw meat and fish, unpasteurized dairy products, and uncooked vegetables. L. monocytogenes has also been found in processed foods including soft, sliced, or grated cheese; deli cold cuts; and ice cream.

Some healthy people might eat Listeria-contaminated foods without developing signs or symptoms of illness; however, in susceptible persons, the infectious dose may be less than 1,000 organisms.

Early-onset neonatal infections (onset ≤6 days after birth) may arise from mother to fetus/infant transmission via the transplacental route or from an ascending intrauterine infection. Late-onset neonatal infections (onset between 7-28 days after birth) can be acquired during passage through the birth canal.

Skin infections may occur from direct contact with infected animals or soil contaminated with infected animal feces. In most human cases, the portal of entry is not apparent. The organism may be shed in human stool for several months.

Period of Communicability

Period of communicability is unknown. Some infected people may excrete L. monocytogenes for several months in their feces. Mothers of infected newborns can shed the organism for 7-10 days after delivery. Vaginal carriage does occur in humans. Listeria has been isolated from human milk. Despite this, person-to-person transmission is rarely seen.

Incubation Period

The incubation period is typically 2-3 weeks after eating food contaminated with Listeria. However, cases have occurred as late as 70 days after exposure or as early as the same day of exposure. Newborns infected during birth develop symptoms a few days to a few weeks later.

Public Health Management

Case

Investigation

When listeriosis cases are identified, the primary goal of local public health jurisdictions is to identify the source of the infection so that others do not get infected. As most cases are acquired by ingestion, an attempt should be made to determine possible contaminated food sources and to collect any remaining food with its packaging for testing at the ODH Laboratory. Clinical isolates from cases should be sent by the hospitals to ODH Laboratory.

The CDC has developed a special initiative to study and prevent listeriosis. To contribute to this effort, state and local investigators are asked to complete a detailed food questionnaire on each reported case: Listeria Initiative Case Report Form (CDC OMB 0920-0728), also available in Spanish.

Treatment

Effective antimicrobial treatment is essential for invasive disease. Please consult the Centers for Disease Control and Prevention (CDC) or a current reference for treatment due to frequently changing recommendations.

Isolation

There is no isolation requirement; standard precautions are recommended.

Contacts

It appears that many people have contact with and carry the organism, but few develop symptomatic infections.

Prevention and Control

There is no immunization available. Prevention relies primarily on food safety. Some additional recommendations are specific to persons who are at high risk for Listeria infection.

General recommendations:

  • Thoroughly cook raw food from animal sources, such as beef, pork, or poultry to a safe internal temperature. For a list of recommended temperatures for meat and poultry, visit IsItDoneYet?.
  • Rinse raw fruits and vegetables thoroughly under running tap water before eating.
  • Keep uncooked meats and poultry separate from vegetables and from cooked foods and ready-to-eat foods.
  • Do not drink raw (unpasteurized) milk, and do not eat foods that have unpasteurized milk in them.
  • Wash hands, knives, countertops, and cutting boards after handling and preparing uncooked foods.
  • Consume perishable and ready-to-eat foods as soon as possible.

Persons at high risk for Listeria infection such as pregnant women, older adults, and persons with weakened immune systems should follow the general recommendations listed above, as well as the following specific recommendations:

  • Meats
    • Do not eat hot dogs, luncheon meats, cold cuts, other deli meats (e.g., bologna), or fermented or dry sausages unless they are heated to an internal temperature of 165°F or until steaming hot just before serving.
    • Avoid getting fluid from hot dog and lunch meat packages on other foods, utensils, and food preparation surfaces, and wash hands after handling hot dogs, luncheon meats, and deli meats.
    • Do not eat refrigerated pâté or meat spreads from a deli, meat counter, or from the refrigerated section of a store. Foods that do not need refrigeration, like canned or shelf-stable pâté and meat spreads, are safe to eat. Refrigerate after opening.
  • Cheeses
    • Do not eat soft cheese such as feta, queso blanco, queso fresco, Brie, Camembert, blue-veined, or panela (queso panela) unless it is labeled as made with pasteurized milk. Make sure the label says, "MADE WITH PASTEURIZED MILK."
  • Seafood
    • Do not eat refrigerated smoked seafood unless it is contained in a cooked dish, such as a casserole, or unless it is a canned or shelf-stable product. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna, and mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked," or "jerky." These fish are typically found in the refrigerator section or sold at seafood and deli counters of grocery stores and delicatessens. Canned and shelf stable tuna, salmon, and other fish products are safe to eat.
  • Fruits and Vegetables
    • Do not eat raw or lightly cooked sprouts of any kind (including alfalfa, clover, radish, and mung bean sprouts); always cook sprouts thoroughly.
    • Eat cut melons right away or refrigerate at 41°F or colder. Discard cut melons after 7 days or if left at room temperature for more than 4 hours.

Recommendations to Keep Food Safe

  • Be aware that L. monocytogenes can grow in foods in the refrigerator. Use an appliance thermometer, such as a refrigerator thermometer, to check the temperature inside your refrigerator. The refrigerator should be 40°F or lower and the freezer 0°F or lower.
  • Clean up all spills in your refrigerator right away, especially juices from hot dog and lunch meat packages, raw meat, and raw poultry.
  • Clean the inside walls and shelves of your refrigerator with hot water and liquid soap, then rinse.
  • Divide leftovers into shallow containers to promote rapid, even cooling. Cover with airtight lids or enclose in plastic wrap or aluminum foil. Use leftovers within 3-4 days.
  • Use precooked or ready-to-eat food as soon as you can. Do not store the product in the refrigerator beyond the use-by date; follow the United States Department of Agriculture (USDA) refrigerator storage time guidelines:
    • Hot dogs: Store opened package no longer than 1 week and unopened package no longer than 2 weeks in the refrigerator.
    • Luncheon and Deli Meat: Store factory-sealed, unopened package no longer than 2 weeks. Store opened packages and meat sliced at a local deli no longer than 3-5 days in the refrigerator.
Revised 5/2023.