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Diagnosis of listeriosis
Medical expert of the article
Last reviewed: 03.07.2025
Diagnosis of listeriosis based on clinical and epidemiological data is difficult due to the polymorphism of clinical manifestations and the impossibility in some cases to identify the source of infection, so laboratory diagnostics are of crucial importance. A preliminary conclusion can be made based on the results of bacterioscopic examination of Gram-stained smears of cerebrospinal fluid sediment and amniotic fluid. However, Listeria spp. cells in Gram-stained smears of cerebrospinal fluid should be differentiated from streptococcal cells, corynebacteria and decolorized Haemophilus influenzae cells, which is not always easy due to their morphological similarity.
A definitive diagnosis of listeriosis can only be made by a bacteriological method. Listeria can be isolated from patients' blood, cerebrospinal fluid, tonsil smears, lymph node punctures, vaginal and cervical canal smears, feces, purulent discharge from the eyes, synovial fluid, etc. If listeria sepsis is suspected, blood is cultured, in meningitis and meningoencephalitis - cerebrospinal fluid, in newborns - meconium. In a woman who has given birth to a stillborn child or a child with signs of listeriosis, the amniotic fluid, placenta, and discharge from the birth canal are examined.
In addition, it is possible to isolate Listeria in smears from the oropharynx and feces of healthy people, which is regarded as asymptomatic carriage.
No special media or cultivation conditions are required to isolate Listeria from sterile biological substrates (blood, cerebrospinal fluid, amniotic fluid): Listeria grows well on blood and chocolate agar, tryptose broth with glucose, and in commercial blood culture bottles. Other types of clinical material (discharge from the tonsils, eyes, female genital tract, feces) are contaminated with a variety of microflora, and the number of Listeria in them may be insignificant, and they can be isolated only using selective nutrient media or an enrichment procedure.
The grown colonies are identified as Listeria monocytogenes based on a combination of morphological and biochemical tests.
Express diagnostics of listeriosis is based on the use of immunochemical methods (RIF, IFA), as well as PCR. Serological diagnostics of listeriosis has not been developed in detail. When determining specific antibodies by currently available methods, both false-negative and false-positive research results occur.
[ Differential diagnosis of listeriosis
Differential diagnostics of listeriosis is carried out with various diseases depending on the clinical form (variant) of listeriosis. In particular, the angina-glandular variant must be differentiated primarily from viral infectious mononucleosis Epstein-Barr, which is characterized by subacute development, a combination of exudative pharyngitis, tonsillitis, polyadenopathy (mainly cervical group) and changes in the hemogram: neutropenia, a significant increase in the number of mononuclear cells, the appearance of atypical mononuclear cells and plasma cells, heterophilic antibodies (in particular, to horse erythrocytes) and to the capsid antigen of EBV. In some cases, adenovirus disease, cytomegalovirus infection, toxoplasmosis should also be excluded.
The gastroenteritic form of listeriosis differs from acute intestinal infections of other etiologies by its more severe course, the prevalence of intoxication symptoms over signs of gastrointestinal damage, and the simultaneous, as a rule, illness of a large number of people who consumed the same product.
The nervous form is differentiated from purulent (less often serous) bacterial forms of meningitis of other etiologies.
The septic form of listeriosis is indistinguishable by clinical data from sepsis caused by other microbes, and sometimes resembles typhoid-paratyphoid diseases, yersiniosis, etc.
Differential diagnostics of listeriosis in pregnant women is carried out with common urinary tract infections, and listeriosis in newborns - from congenital cytomegalovirus infection, toxoplasmosis, streptococcal sepsis, syphilis. The presence of listeriosis in a pregnant woman can be assumed by "habitual" spontaneous abortions in the anamnesis, unmotivated fever, a critical decrease in body temperature after termination of pregnancy (spontaneous abortion, childbirth), the death of the child soon after birth.