In the old days, epidemics of such a serious infectious disease as typhoid fever led to the death of thousands of human lives. Due to strict sanitary and epidemiological control, outbreaks of this dangerous intestinal infection in our country have not been observed for a long time. However, in African, Asian and South American countries with hot climates, the incidence of typhoid fever is still very high. The ideal habitat for the causative agent of this disease (typhoid salmonella from the enterobacteriaceae family) is polluted water bodies, poorly purified drinking water, improperly stored dairy and meat products, where harmful microorganisms begin to multiply actively at high air temperatures. The bacterium is excreted in the feces of the bacillus carrier and enters the mouth of a healthy person through dirty hands, food, or common objects (fecal-oral route of infection). To identify this infectious pathogen, laboratory tests of urine, feces, bile are carried out, and a blood test for typhoid fever is also prescribed.
Indications for testing
First of all, typhoid salmonella affects the intestines, then the regional (nearby) lymph nodes, after which it enters the circulatory system and causes general intoxication of the body. The indications for donating blood for the detection of this bacterium are high body temperature, headache, depression, weakness, dry tongue, pain in the right hypochondrium, red rashes on the abdomen (roseola), clouding of consciousness. Laboratory blood tests when diagnosing this pathology are mandatory, since similar symptoms are also characteristic of pneumonia, malaria,.
Hemogram
This term hides a general clinical blood test, which is an integral part of diagnostic procedures for any infectious disease. The following indicators may indicate the presence of typhoid fever: the level of leukocytes in the blood is greatly reduced (leukopenia), eosinophils are absent, and the erythrocyte sedimentation rate (ESR) is increased.
Bacteriological examination
Next comes the turn of the direct detection of the typhoid pathogen (hemoculture). For this purpose, venous blood is taken, inoculated on a special nutrient medium and placed in a thermostatic apparatus, in which a high temperature is created. Under the influence of heat, whole colonies of bacteria are formed, suitable for microscopic examination. Blood culture is considered the most accurate early diagnostic method for detecting typhoid fever.
Immunological research
Since the immune system must respond to the introduction of a foreign agent, by about the end of the first week of the disease, antigens and antibodies to the infectious agent begin to form in the blood. For immunological research, blood serum is separated, in which the titer (level) of antibodies is determined. This analysis is called the passive hemagglutination reaction (RPHA). In a sick person, the antibody titer can be 1:40, and in a recovering person it can be up to 1: 2000, so this blood serum test is carried out every 5 days.
Preparation for the test
In order for the results of general clinical, bacteriological and immunological studies for typhoid fever to be reliable, it is necessary to prepare appropriately for the delivery of a blood test. If there is such a possibility, then three days before the procedure, it is advisable to stop taking any medications. Alcoholic drinks are prohibited two days before laboratory tests. On the day of visiting a blood donation point, you will have to stop eating dairy products, eggs, butter, fried, smoked and spicy foods. An hour before the tests, you need to refrain from the bad habit of smoking. All these factors can cause biochemical, metabolic and hormonal changes in the body that can change laboratory parameters.
A blood test for typhoid fever is a necessary procedure for making a correct diagnosis, but it is better to prevent the development of this dangerous disease. It is necessary to monitor the cleanliness of your hands, wash fruits and vegetables thoroughly, avoid eating street food products, and fight flies - active carriers of this infection. It is especially important to strictly observe sanitary and hygienic rules for workers in the food industry, kindergartens and medical institutions.
Typhoid fever is a dangerous disease of an infectious nature, the causative agent of which is Salmonella S.typhi. You can catch typhoid fever through food, infected water, if simple hygiene rules are not followed (through unwashed hands), as well as from the carrier of the infection.
The initial signs of typhoid fever are in many ways very similar to various other infectious diseases, therefore, if there is a suspicion of the presence of this infection in the body, it is necessary to make an analysis for typhoid fever without fail for accurate diagnosis. Only in this way can the fact of infection be confirmed and effective treatment can be prescribed in a timely manner.
Indications for prescribing a blood test for typhoid fever
It is required to be tested for typhoid fever if the following symptoms appear:
- Attacks of nausea, vomiting, abdominal pain.
- Signs of intoxication of the body: insomnia, loss of appetite.
- Unstable stools: constipation or, on the contrary, diarrhea.
- Feeling of general malaise and weakness.
- Dehydration symptoms: dry skin, thirst, "coated" tongue.
- A gradual increase in body temperature turning into a fever.
The presence of typhoid fever is determined based on the indications of laboratory tests, anamnesis data (interviewing the patient), which may indicate characteristic signs of the disease and contact with the carrier of the infection. To prevent the appearance of typhoid fever and comply with standard sanitary standards, a blood test for typhoid is taken by the working personnel of medical institutions, preschool institutions, as well as workers in the food industry, trade in various food products, etc. once a year.
What tests are prescribed to diagnose typhoid fever?
If there are signs of illness, a blood test for typhoid should be taken before taking antibiotics. This condition is explained by the fact that after 2-4 days from the start of treatment, a blood test may give a negative result. In general, a number of the following tests are usually assigned for such a study:
- Serological blood test(Vidal's reaction). With its help, it is possible to detect antibodies to the causative agent of typhoid fever on the 4th-5th day of illness.
- General blood analysis... Such an examination is usually prescribed in the first days of the disease, but it indicates the presence of typhoid fever only indirectly.
- Blood chemistry- detects proteins of the acute phase.
- Bacterial culture- the results of such a blood test can be obtained only after 4–5 days.
To detect antibodies to typhoid, methods of radioimmunoassay and enzyme immunoassay are used. The most common test method used to detect carriers of infection among food industry workers and to assess the effectiveness of vaccination against typhoid fever is the method of research using RNGA (indirect hemagglutination test). The material for this analysis is venous blood. In order to obtain the most accurate data, it is forbidden to smoke 30 minutes before passing the RNGA analysis.
With a positive outcome of a blood test for typhoid, we can talk about an acute course of the disease, or about an infection that has already been transferred. In addition, a positive result may indicate that the person is a carrier of the causative agent of typhoid fever. If the test results are negative, the doctor can conclude that a long time has elapsed after recovery, the early form of the disease (in the presence of appropriate clinical manifestations), or even the absence of infection in the body. A false-positive test for typhoid is possible in the presence of cross-reactions with other pathogens of infectious diseases from the genus Salmonella.
How to properly prepare for testing for typhoid fever?
The main factors that affect the typhus blood test result include:
- Eating... On the day of testing for typhoid fever, it is not recommended to eat fried, spicy, smoked and fatty foods, as well as butter, dairy products and eggs. With such an unhealthy diet, it is possible both a direct effect on the blood composition due to the absorption of food components, and an indirect effect of the turbidity of the sample, shifts in the level of hormones.
- Alcohol... Two days before donating blood for analysis, it is forbidden to drink alcohol, since it has an acute and chronic effect on many metabolic processes.
- Smoking... One hour before visiting the blood donation point for analysis, you must refrain from smoking. The fact is that this bad habit changes the secretion of biologically active substances, which negatively affects the research results.
- Emotional and physical overload- cause biochemical and hormonal changes.
- Instrumental examinations, physiotherapy - may temporarily change laboratory parameters.
In addition, when taking blood, the time of day is very important: each person has certain daily rhythms of activity and, in accordance with this, daily fluctuations in many biochemical and hormonal parameters, expressed to a lesser or greater extent for different indicators. If possible, it is advisable to donate blood for analysis on an empty stomach (at least 8 hours and not more than 14 hours of hunger, you can drink water as usual), avoid food overload the day before. The most optimal time for blood tests for typhoid fever is in the morning, from 8 to 11 hours.
4.50 out of 5 (5 Votes)Typhoid fever is a serious infectious disease caused by S. typhi salmonella. You can become infected with typhoid fever through infected water, food, if basic hygiene rules are not followed (through dirty hands), as well as from a healthy carrier of the infection.
The initial symptoms of typhoid fever can be very similar to many other infectious diseases, therefore, if an infection is suspected for an accurate diagnosis of typhoid fever, it is necessary to pass an analysis without fail - this is the only way to timely identify the fact of infection and prescribe appropriate treatment.
Indications for analysis
An analysis for typhoid fever must be passed when the following symptoms appear:
- feeling of weakness and general malaise;
- a gradual increase in body temperature, by the third or fifth day after the onset of the malaise, turning into a fever;
- signs of body intoxication: loss of appetite, insomnia;
- signs of dehydration: "coated" tongue, thirst, dry skin;
- abdominal pain, vomiting, nausea;
- unstable stools: diarrhea and constipation.
Typhoid fever is diagnosed based on the history data, which may indicate contact with a sick person, characteristic symptoms of the disease and the results of laboratory tests.
In order to comply with sanitary standards and the prevention of typhoid fever, employees of preschool and medical institutions, catering and food industry, food trade enterprises take analysis once a year.
What tests are prescribed
In the presence of symptoms of the disease, a blood test for typhoid should be taken before starting antibiotics, since after two to four days from the start of treatment, a blood test may show a negative result. For research, a number of the following tests can be assigned:
- a general blood test: it can be prescribed in the first days of the disease, but indicates the presence of typhoid fever only indirectly;
- a blood culture test, in which results can be obtained only after 4-5 days, and bacteriological tests of other body fluids;
- biochemical blood test: in the presence of typhoid fever, it shows proteins of the acute phase;
- a blood test that detects the titer of antibodies to the causative agent of the disease;
- serological blood test for typhus (Vidal's reaction): allows you to detect antibodies to the causative agent of the disease on the fourth to fifth day of the disease.
To detect antibodies to typhoid fever, methods of enzyme immunoassay and radioimmunoassay of blood are also used.
Indirect hemagglutination test (IRH) testing is the most common typhoid test and is used to identify carriers of the infection among food workers. The material for this analysis is venous blood. Do not smoke 30 minutes before the analysis of RNGA.
Decryption
A positive blood test result for typhoid fever can indicate both an acute course of the disease, and an infection that has already been transferred, or that a person is a carrier of the causative agent of the disease. In case of negative results, the doctor can draw conclusions about the absence of infection, an early form of typhoid fever (if there are appropriate clinical manifestations), or a long period of time after recovery.
A false positive test result is likely in the presence of cross-reactions with other infectious agents of the genus Salmonella. Also, factors such as hemolysis of the sample and antibiotic therapy (taking antibiotics) may affect the test results.
How are typhoid tests done? What are they? Typhoid fever is referred to as acute intestinal infections, but it stands alone. Usually, with intestinal infections, students begin to study the course of infectious diseases, and the first of them is usually typhoid fever and paratyphoid fever A and B, the causative agents of which form the typhoid paratyphoid group.
Why does the study of this difficult course begin with typhoid fever? Yes, because this disease develops in clearly defined stages, proceeds predictably, the tests for typhoid fever and the principles of diagnosis are standard and uncomplicated, and using the example of typhoid fever, one can fully get acquainted with the typical course of an acute intestinal infection.
About typhoid fever
Where does typhoid fever come from? It is a disease of dirty hands and contaminated water. The causative agent of typhoid fever is a large microorganism Salmonella from the genus Enterobacteriaceae, and the causative agent of typhus is extremely small rickettsia.
Usually, when they talk about typhoid, the harsh years of the civil war come to mind. But then there were epidemics, mainly typhus. And nowadays every year more than 20 million people, or the population of two cities like Moscow, are infected with typhus. Almost 900 thousand of them die every year. Such outbreaks occur in hot countries in Africa, India, Colombia and Malaysia, Indonesia and Afghanistan. Therefore, a great danger lies in wait for those travelers who underestimate the likelihood of infection.
It is very easy to get infected with typhoid fever, and the severity of this disease lies, first of all, in the fact that it begins as a slight malaise with ordinary food poisoning. Such features of this infection have led to the fact that all the so-called decreed persons working in the food industry, in educational institutions and medical organizations must annually take tests for typhoid fever and be checked for the carriage of typhoid bacilli. The same research should be carried out by persons working in the food trade.
Features of the course of infection
Typhoid fever proceeds with a gradually increasing high temperature, the appearance of abdominal pain, general symptoms of intoxication, characteristic of all infections. A feature of typhoid fever is the multiplication of pathogens that have penetrated the intestinal wall into the intestinal immune defense organs - into the lymphatic follicles, into the liver, into the cells of the immune defense. In these follicles, pathogens multiply, and then they enter the bloodstream through the thoracic lymphatic duct, and this coincides with the onset of the acute period of the disease. The characteristic danger of typhoid fever is intestinal bleeding, intestinal perforation or necrosis of the lymphatic follicles.
At the same time, typhoid fever is a unique disease that requires a cavity operating room in an infectious diseases hospital. The fact is that a patient diagnosed with typhoid fever and intestinal bleeding should never be hospitalized in the general surgical department, since it is very contagious. Therefore, in an infectious diseases hospital, a special operating room is equipped for such a case, and, if necessary, surgeons are called upon to perform an emergency operation.
Typhus is transmitted only by humans; you cannot catch typhoid from animals. You can get sick, I communicate not only with the sick, but also with a healthy carrier. One of the most famous figures in history is the so-called "typhoid Mary". Clinically healthy, she worked as a cook in the early 20th century in the United States and, as a result of her food-related work, a total of about 47 people died, whom she personally infected. Typhoid pathogens multiplied in her gallbladder and released into the environment along with feces. The situation was aggravated by the fact that she refused to be examined and denied the preventive value of hand washing.
But a huge number of victims that regularly appear to this day in countries with hot climates and low living standards are associated with the use of food and, above all, with infected water and milk, which are contaminated with feces and sewage in the absence of a centralized sewage system.
The outcome of typhoid fever can be both recovery and transformation of the patient into a chronic carrier. No more than 5% of all those who have been ill become chronic carriers, and this causes a certain epidemiological danger.
Types of tests for typhoid fever
The most important thing to remember: a 100% positive result is only the release of typhoid rods from the patient's blood at the height of the disease, when Salmonella overcome the protective barriers of the intestinal lymphatic follicles and a state of bacteremia occurs. Starting from the second week of the illness, it becomes possible to determine the typhoid sticks in the feces. Of course, the probability of detecting microorganisms depends on the antibiotic treatment and on the initial concentration of microbes in the biological material.
By the end of the first week after the illness, typhoid fever can be determined by examining the patient's blood antibodies that are accumulated to the salmonella antigens of the typhoid pathogen. This and, which are carried out in the analysis of blood serum. The specificity of these tests is lower, since it does not directly detect the pathogen. There may be false positive tests for typhoid fever if the patient has had this disease before.
It should be borne in mind that there are many salmonella pathogens for humans. After suffering salmonellosis, there may be a cross-reaction, as with some shigellosis or bacterial dysentery. Therefore, in the serological diagnosis of typhoid fever, as in the case of almost all bacterial infections, it is very important to repeat the blood test for typhoid fever after about a week in order to detect an increase in titer, that is, a sharp increase in the amount of antibodies. This is what will characterize the acute infectious process and then the diagnosis will be confirmed.
Looking ahead, it must be said that it is never used to confirm the diagnosis of typhoid fever. It can show the general symptoms of an acute infectious process: the presence of increased leukocytosis, an increase in the erythrocyte sedimentation rate, and in severe cases and the development of infectious-toxic shock, leukopenia and other signs of toxic suppression of the function of the red bone marrow may occur. But a general blood test is clearly not enough to make a diagnosis. We list the main methods of laboratory research, with the help of which typhoid is diagnosed in patients and in clinically healthy carriers:
- Method for isolating blood culture (bacteriological blood test).
Blood culture allows you to get positive results already in the first days of the disease. This is a time-consuming but inexpensive method. The causative agents of typhoid fever mature well on media that contain bile broth. If you combine a bacteriological study with the immunofluorescence method (RIF), then the culture of the typhus pathogen grown within 12 hours can already be preliminarily identified, but then it is imperative to wait for confirmation in the classical way. Usually, blood should be taken in an amount not exceeding 20 ml.
Despite the emergence of new diagnostic methods, such as, the method of isolating blood culture has not lost its practical value. It is not enough for the doctor to know that the pathogen of typhoid is in the patient's blood. He needs to know what antibiotics can be used to quickly get rid of the aggressive microorganism. Typhoid bacilli, just like any other microbes, are constantly "improving" and acquire drug resistance to various antibiotics. The isolated pure culture makes it possible to determine the sensitivity of the pathogen to antibacterial drugs. This allows, after receiving a preliminary analysis, to begin targeted treatment, to change empirical therapy to rational, which, of course, will speed up the patient's recovery.
- Bacteriological examination of duodenal contents, feces and urine.
These tests are extremely important, as they allow you to identify healthy carriers from among those who have had previous illnesses. Therefore, before being discharged from the hospital, the patient must submit feces and urine for bacteriological examination, and if the bacterial cultures are negative, then the patient is discharged. How is bile taken? In the same way, on average, 7 days before the planned discharge from the hospital, the patient undergoes diagnostic duodenal intubation. In portions of gallbladder bile, a search for pathogens is carried out, for which bile is also inoculated on nutrient media. In the so-called typhoid Mary, the causative agents of typhoid fever in the gallbladder remained for life, which multiplied and posed a threat to others.
3 months after discharge from the infectious diseases hospital, a bacteriological examination of feces, urine and bile is again carried out, since all those who have been ill are registered with an infectious disease specialist. If at least one analysis for typhoid fever after discharge showed the presence of the pathogen, then the patient is hospitalized for sanitary and epidemiological indications and treated as a carrier. And only if all the culture results were negative, the patient is removed from the register. In the same case, if the patient works in the food industry, in educational or medical institutions, then he is under special supervision throughout his work activity, regularly donating feces to the disgroup and typhoid;
Since serological research methods associated with the detection of antibodies can show their presence in persons who have been ill for a long time, it is necessary to repeat them after a few days in case of an acute illness. An enzyme-linked immunosorbent assay is shown for severe gastroenteritis with an unclear course, in the presence of fever, which is combined with diarrhea and bradycardia. Slowing heart rate (bradycardia) is a very characteristic symptom of typhoid fever, caused by the action of antigens and toxins of this pathogen. ELISA is also used to track the dynamics of an acute process, in patients during dispensary observation, after a previous illness, as well as for the initial detection of carriers of infection;
- Vidal's reaction.
For many years, the classic serological reaction, which has entered all textbooks, is the Vidal reaction. How to take this test? Simply by donating venous blood, which is then centrifuged to obtain serum. Vidal's reaction is a study of the patient's blood serum, which contains antibodies, with a special typhoid diagnosticum. Its role is performed by standardized ram erythrocytes, on which antigens of typhoid pathogens are artificially applied, or, in scientific terms, these erythrocytes are sensitized.
After mixing the components, the mixture is incubated for 2 hours at body temperature, and when the antibodies bind diagnostic erythrocytes, a precipitate appears in the form of whitish flakes, then the reaction is considered positive. The disadvantages of this reaction are obvious: it uses biological material, it is necessary to carefully observe the temperature conditions, as well as certain quantities to exclude false positive values. At present, Vidal's reaction will be superseded by the methods of enzyme-linked immunosorbent assay for which it is not necessary to use sheep erythrocytes.
Interpretation of results
Most often, a blood test for typhoid fever is taken by healthy people who get a job in various food industries or receive a health certificate to work as a food seller. If the result is negative, then most likely the person is healthy and has never been sick.
But in the event that the patient is taken to the hospital with diarrhea, with intoxication and with an unclear picture, then in the first four or five days of typhoid fever, he may also have negative results, since the antibodies have not yet had time to accumulate.
If typhoid antibodies are detected in the patient's blood, then the titer must be indicated as a result of the analysis. In the case of a positive analysis, only four scenarios are possible: these are:
- acute illness;
- a long-standing infection, when circulating antibodies remain for life;
- chronic carriage;
- occasionally false-positive cross-reactions occur, after suffering salmonellosis, for example.
Therefore, patients with positive results of serological diagnosis must be examined using classical methods. How much research is done in this case? This is a bacteriological method for examining urine and feces and the contents of the gallbladder. Blood culture, as an analysis for typhoid fever, is taken almost exclusively when there are signs of the disease.
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