With likely all 11 reported Listeria cases linked to peaches hospitalized, what is happening to them?
Who is most susceptible to Listeria infection?
Several segments of the population are at increased risk and need to be informed so that proper precautions can be taken. The body’s defense against Listeria is called “cell-mediated immunity” because the success of defending against infection depends on our cells (as opposed to our antibodies), especially lymphocytes, otherwise known as “T-cells.” Therefore, individuals whose cell-mediated immunity is suppressed are more susceptible to the devastating effects of listeriosis, including HIV-infected individuals, who have been found to have Listeria-related mortality of 29%. The incidence of Listeria infection in HIV-positive individuals is higher than in the general population. One study found that:
The estimated incidence of listeriosis among HIV-infected patients in metropolitan Atlanta was 52 cases per 100,000 patients per year, and among patients with AIDS it was 115 cases per 100,000 patients per year, rates 65-145 times higher than those among the general population. HIV-associated cases occurred in adults who were 29-62 years of age and in postnatal infants who were 2 and 6 months of age.
Pregnant women naturally have a depressed cell-mediated immune system. While other systemic bacterial infections may result in adverse pregnancy outcomes at comparable frequencies, L. monocytogenes have notoriety because fetal complications largely occur in the absence of overt illness in the mother, delaying medical intervention. In addition, the immune systems of fetuses and newborns are very immature and are extremely susceptible to these types of infections.
Other adults, especially transplant recipients and lymphoma patients, are given necessary therapies with the specific intent of depressing T-cells, and these individuals become especially susceptible to Listeria as well. Other adults, especially transplant recipients and lymphoma patients, are given necessary therapies with the specific intent of depressing T-cells, and these individuals become especially susceptible to Listeria as well.
According to the FDA, CDC, and other public health organizations, individuals at increased risk for being infected and becoming seriously ill with Listeria include the following groups:
- Pregnant women: They are about 10-20 times more likely than other healthy adults to get listeriosis. About one-third of listeriosis cases happen during pregnancy. Fetuses are also highly susceptible to infection and severe complications.
- Newborns: Newborns can develop life-threatening diseases from perinatal and neonatal infections
- Persons with weakened immune systems
- Persons with cancer, diabetes, kidney, or gastrointestinal disease
- Persons with HIV/AIDS: Individuals with HIV/AIDS are almost 300 times more likely to get listeriosis than people with healthy immune systems.
- Persons who take glucocorticosteroid medications (such as cortisone)
- Persons of advanced age: One risk assessment showed people over 60 years old were 2.6 times more likely to develop listeriosis than the general population. And in 2011, the median age of diagnosed cases in people who were not pregnant was 71 years old.
Symptoms of Listeriosis
Only a small percentage of persons who ingest Listeria fall ill or develop symptoms. For those who do develop symptoms because of their infection, the resulting illness is either mild or quite severe,  Listeria can cause two different types of disease syndromes with differing severity. Non-invasive Listeria infection causes gastroenteritis with symptoms such as diarrhea, nausea, and vomiting that resolve on their own. Healthy adults without any immunocompromising conditions typically experience this milder version of the disease. The more severe type of disease caused by Listeria monocytogenes is called listeriosis and is referred to as an invasive illness.
On the mild end of the spectrum, listeriosis usually consists of the sudden onset of fever, chills, severe headache, vomiting, and other influenza-type symptoms. Along these same lines, the CDC notes that infected individuals may develop fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea or diarrhea. When present, the diarrhea usually lasts 1-4 days (with 42 hours being average), with 12 bowel movements per day at its worst.
The more severe form of the illness occurs when the bacteria infect parts of the body that are typically sterile, such as the blood, brain, liver, and cerebral spinal fluid. The presence of the bacteria in these areas triggers the immune response and can lead to those more severe symptoms. L. monocytogenes has a specific affinity for the central nervous system (CNS), especially in cell-mediated immunodeficient individuals.
As already noted, when pregnant, women have a mildly impaired immune system that makes them susceptible to Listeria infection. If infected, the illness appears as acute fever, muscle pain, backache, and headache. The illness usually occurs in the third trimester, which is when immunity is at its lowest. Infection during pregnancy can lead to premature labor, miscarriage, infection of the newborn, or even stillbirth. Around twenty percent of such infections result in stillbirth or neonatal death.
Newborns may present clinically with early-onset (less than 7 days) or late-onset forms of infection (7 or more days). Those with the early-onset form are often diagnosed in the first 24 hours of life with septicemia, meningitis, or respiratory distress and have a higher mortality rate. Early-onset listeriosis is most often acquired through trans-placental transmission. Late-onset neonatal listeriosis is less common and less severe than the early-onset form. Clinical symptoms may be subtle and include irritability, fever, poor feeding, and meningitis. The mode of acquisition of late onset listeriosis is poorly understood.
Complication of Listeria Infection
For those persons who suffer a Listeria infection that does not resolve on its own, the complications can be numerous and possibly severe. The most common complication is septicemia (bacterial infection in the blood), with meningitis being the second most common. Other complications can include inflammation of the brain or brain stem (encephalitis), brain abscess, inflammation of the heart-membrane (endocarditis), septic arthritis, osteomyelitis (infection in the bone), and localized infection, either internally or of the skin.
Death is the most severe consequence of listeriosis, and it is tragically common. The CDC has estimated that L. monocytogenes is the third leading cause of death from foodborne illness, with approximately 260 of 1,600 people diagnosed dying from their infections. For example, based on 2018 FoodNet surveillance data, 96% of 126 Listeria cases ended up in the hospital, the highest hospitalization rate for pathogenic bacterial infection. This data showed a fatality rate of 21%. According to the FDA, the case-fatality rate increases substantially based on complications, possibly reaching rates of 70% in cases with listeria meningitis, 50% in septicemia cases, and over 80% for perinatal/neonatal infections. In one US study, L. monocytogenes was reportedly the cause of nearly 4% of all cases of bacterial meningitis.
 Waldron, C. M. (2017, September 15). The Recovery and Transfer of Aerosolized Listeria Innocua. https://vtechworks.lib.vt.edu/handle/10919/78907.
 Arslan, F., Meynet, E., Sunbul, M., Sipahi, O. R., Kurtaran, B., Kaya, S., … Mert, A. (2015, June). The clinical features, diagnosis, treatment, and prognosis of neuroinvasive listeriosis: a multinational study. European journal of clinical microbiology & infectious diseases: official publication of the European Society of Clinical Microbiology. https://www.ncbi.nlm.nih.gov/pubmed/25698311.