How Do You Know If You Have Listeria?

Listeriosis, a disease caused by Listeria monocytogenes, is fundamentally a disease transmitted by food, notifiable, that can be difficult to diagnose.

The listeria species are widely spread in the environment, isolating itself from the soil, putrefactive plant material, wastewater, animal feed, fresh and frozen chicken, fresh and processed foods, cheese, unprocessed milk, slaughterhouse waste, as well as in the human digestive tract and asymptomatic animals. That is why it has many opportunities to contaminate food in different steps of production, this being the most frequent route by which the human being acquires colonization or infection. In fact, it is part of the fecal flora of many mammals, it is estimated that between 1% and 10% of humans are intestinal carriers of L. monocytogenes.

To reach the diagnosis of listeria, there must be a high suspicion by the doctor. To be able to make a definitive diagnosis, it is necessary to identify the causative microorganism in a sample that usually must be sterile, as in any other infectious disease. The sample to be collected depends on the clinical presentation.

Listeriosis caused by listeria can occur sporadically or in outbreaks. The infection causes a spectrum of diseases ranging from febrile gastroenteritis to invasive disease, which includes bacteremia, sepsis, meningitis, and meningoencephalitis, mainly in patients with risk factors for L. monocytogenes.

Listeria is a bacterium that mainly affects susceptible guests, such as the elderly, newborns, immunosuppressed and pregnant women; although it affects people without clear risk factors.

The incidence of listeriosis which is caused by listeria is not high, but is increasing in recent years, mainly because of the increase in the old population or with predisposing factors. Other less frequent clinical presentations, but also described are endocarditis, lymphadenitis, cellulitis, pneumonia, osteomyelitis, arthritis, conjunctivitis, and mycotic aneurysm.

Listeriosis caused by listeria has a high mortality despite the adequate and precocious treatment, and this is related to a complex diagnosis due to multiple aspects.

First, L. monocytogenes can contaminate a wide variety of foods. Secondly, the incubation period is variable and prolonged (1 to 70 days), being able to be even higher in pregnant women than in cases with central nervous system (CNS) commitment.

In the presentations with gastroenteritis, the incubation can be less than 6 hours and up to 10 days. In fact, it is proposed to consider a 14-day exposure window for the diagnosis of cases of CNS and bacteremia and 6 weeks in associated cases with pregnancy. Third, many products can retain bacteria for several days or weeks and, therefore, can be consumed by the patient on multiple occasions.

L. monocytogenes has differentiated into more than 10 serotypes; being some of them involved in most reported cases of human listeriosis, and some of them more involved in outbreaks, they can even be considered epidemic clones.

The diagnosis of listeriosis caused by listeria is difficult. The main thing for doctors is having the suspicion of this causal agent. The history and the physical examination as well as taking into account the most susceptible populations are fundamental as well as taking the necessary clinical samples, mainly blood cultures. Bacteremia can be classified as primary or secondary; therefore, it is also important to collect other samples as a cerebrospinal fluid (CSF), peritoneal fluid, placenta, and others according to the clinical manifestations. In addition to the host factors, the specific pathogenic factors also seem to be important in the cause of the disease, and for this reason, it is the different clinical presentations.

It is noteworthy that in meningitis due to L. monocytogenes, unlike other bacterial meningitis, it is frequent to present with a clear or slightly opalescent CSF, with less than 1000 cells/mm3 and with a significant, sometimes predominant, percentage of lymphocytes.

The identification of L. monocytogenes is carried out using standard microbiological techniques. The Bacteria grow in 24 to 48 hours, forming small rounded colonies and present β-hemolysis on blood agar.

Serological tests can be useful, particularly in the study of carrier patients and in the study of outbreaks.

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