Q fever: diagnosis
Last reviewed: 23.04.2024
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Laboratory diagnostics of ku-fever is based on serological methods: RA, RSK, RNIF, the results of which are analyzed taking into account the phase variations of coxial cells, which allows differentiating patients and recovered (diagnostic standard).
The most simple and sensitive test - RA is used in macro- and micromodification. Agglutinins are found on the 8-10th day of the disease in diagnostic titres 1: 8-1: 16. The maximum titers (1: 32-1: 512) are noted by the 30-35th day of the disease. Then, gradually decreasing, they persist in the body that has recovered from several months to several years.
In clinical practice, the most widely used DSC. Detection of complement-binding antibodies depends on the phase state of the corpuscular antigen of the Burnett coxiella used in the reaction. Antibodies to the antigen of the second phase indicate an acute, "fresh" pathological process, arise from the 9th day of the disease and persist until 11-23 years, and the antibodies of the first phase appear from the 30th day and last no more than 2-3 years. Identification of antibodies to both phase variants of coxial cells indicates either a chronic form of the disease or anamnestic character of the reaction, rather than a disease in a given period of time. A high concentration of antibodies to the antigen of the first phase indicates a chronic infection and is characteristic of patients with subacute or chronic coxular oesophageal endocarditis. Antibodies in RSK are detected later than in RA. The highest titers (1: 256-1: 2048) are recorded on the 3-4th week from the onset of the disease. They persist for a long time - 3, 5, 7, 11 years. For differentiation of markers of acute process and "anamnestic" antibodies, examination in dynamics ("paired sera") is necessary; confirmation of the disease is a 2-4-fold increase in the titer.
Recently, RNIF is increasingly used, since antibodies in this reaction are detected earlier than in RA.
Thus, the diagnosis of ku-fever is based on the identification of a complex of clinical, epidemiological and laboratory data.
[Differential diagnosis of ku-fever
In connection with the polymorphism of symptoms, clinical diagnosis of ku-fever is extremely difficult and is possible only in endemic foci in the presence of epidemic morbidity.
Differential diagnosis of ku-fever is carried out with influenza, typhus and typhoid, brucellosis, ornithosis, pneumonia of various etiologies, jaundice leptospirosis, sepsis.
When the lungs are affected, it is necessary to differentiate the disease from tuberculosis (especially if the foci are located in the upper parts of the lungs). With ku-fever with scant clinical symptoms, significant x-ray changes are possible already in the first days of the disease.
Influenza from ku-fever is distinguished by a more acute onset and severe intoxication, the presence of muscle pain in the absence of articular, a short-term febrile reaction, a permanent tracheitis, the absence of hepatosplenomegaly, a pronounced contagiousness.
Ku-fever is characterized by a significant similarity with typhoid paratyphoid diseases (gradual onset, prolonged fever, bradycardia, pulse dicrotia, language change, hepatosplenomegaly, hemogram). From typhoid fever it is characterized by less pronounced toxicosis, almost constant absence of a rash and a positive symptom of Padalka, less expressed hepatosplenomegaly, an earlier occurrence of a typhoid status, negative results of a serological and bacteriological examination.
Differential diagnosis of ku-fever is carried out with chronic forms of brucellosis on the basis of a characteristic lesion of locomotor apparatus, nervous system, internal organs, genitourinary system and the presence of fibrositis in brucellosis.