Laboratory diagnosis of intestinal infections

Clinical Guidelines for Ordering Tests

Establishing a preliminary diagnosis (most commonly a typhoid-paratyphoid disease, more likely typhoid fever) is based on three leading clinical syndromes. These serve as the rationale for ordering specific laboratory tests.

1. Prolonged intoxication syndrome. Manifests as high fever, pronounced general weakness, headache, as well as sleep and appetite disturbances. The patient is lethargic and adynamic. Cardiovascular examination reveals hypotension and relative bradycardia (e.g., rhythmic pulse, around 76 bpm against the background of high fever). Heart sounds are muffled on auscultation.
2. Signs of infection generalization. Include hepatolienal syndrome (combined enlargement of the liver and spleen — hepatosplenomegaly) and the appearance of a rash.
3. Signs of gastrointestinal tract involvement. A specific tongue appearance is characteristic: it is dry, with clean tip and edges while the central part is coated. The abdomen is moderately distended, palpation clearly reveals gurgling in the right iliac region, and stool disorders are observed.

Note: neurological status in such patients is generally unremarkable — meningeal and focal symptoms are absent. The respiratory and urinary systems function without pathology in uncomplicated cases.

Methods of Laboratory Confirmation

A set of laboratory studies is used to confirm clinical suspicions. Initially, a basic complete blood count (CBC) is ordered to assess the general reaction of the body. However, bacteriological examination, aimed at direct isolation of the pathogen from various biological fluids, is of decisive importance.

The physician orders:

• Blood culture to obtain hemoculture;
• Stool examination to isolate coproculture;
• Urine culture to isolate uroculture.

Along with bacteriological methods, serological diagnostics (immunological tests) are mandatory, allowing the detection of specific antibodies against the pathogen in the patient's blood serum.

Differential diagnosis

Since the clinical picture of typhoid fever is not always specific in the early stages, differential diagnosis is performed with a wide range of diseases presenting with prolonged high fever and pronounced intoxication.

First, other severe infections are ruled out:

• Typhus;
• Generalized forms of salmonellosis;
• Sepsis;
• Malaria.

It is also necessary to differentiate the condition from somatic and inflammatory pathologies capable of producing a similar febrile response, such as severe pneumonia and acute pyelonephritis.

Epidemiological History and Management Tactics

Thorough collection of the epidemiological history is critically important to refine the diagnosis. It is important to ascertain the patient's living conditions (urban or rural residence, type of housing, dietary habits) and contacts. A key risk factor is cohabitation with a person registered as a chronic bacterial carrier of the typhoid bacillus (e.g., if a family member has had the infection in the past).

Algorithm of actions upon identifying a patient:

1. Hospitalization: the patient is subject to mandatory hospitalization in an infectious diseases hospital. This is necessary both for comprehensive examination and treatment, and for reliable isolation.
2. Anti-epidemic measures: mandatory terminal disinfection is carried out in the focus of infection (the patient's apartment).
3. Work with contacts: relatives and individuals living together with the patient are thoroughly briefed on the mechanisms, transmission routes of the infection, and basic prevention measures.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Classification of Salmonella
• Properties of the Typhoid Fever Pathogen
• Antigenic Structure of Bacteria
• L-form Transformation of the Pathogen
• Sources, Mechanisms, and Routes of Infection Transmission

Other topics in the "Acute Intestinal Infections" section

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