Screening study for HIV. Screening and testing for HIV antibodies

The diagnosis of HIV infection can be established in the laboratory by detecting specific antibodies to the virus. In many other viral diseases, the presence of antibodies indicates a past infection. However, since HIV infection develops chronic infection, seropositive individuals are not only actively infected, but also contagious.

A serological test for detecting the presence of antibodies to HIV became widely available in 1985. The most commonly used method is enzyme-linked immunosorbent assay (ELISA), but other types of antibody tests are being developed, such as particle agglutination and "dot" ELISA. Tests can be performed quickly and easily and do not require complex equipment.

Although the above tests are highly sensitive, they can also give false results and positive result needs further confirmation with an additional test such as Western blot or indirect immunofluorescence.

It is also possible to directly determine HIV antigens (virus or viral protein) in semen; industry produces the necessary sets of reagents. These assays were originally designed as an attempt to provide a laboratory indication of the presence of infection during the "window" between infection and antibody production, which typically lasts 4 to 16 weeks. Antigen assays are now being used more widely to monitor the outcome of antiviral treatment in AIDS patients.

Screening programs for HIV infection (i.e. screening the entire population, or specific subpopulations to determine infection or disease) can help:

prevent transmission of the virus through blood and blood products, semen, tissues or organs for transplantation;
obtain epidemiological information on the prevalence and incidence of HIV.

Whenever a screening program is discussed, all questions noted in the WHO statement (Annex 4) should be clearly stated and addressed. Poorly designed and poorly implemented programs can harm public health and waste resources. Public health needs and human rights are best served by careful consideration of a range of technology, logistics, and social, legal and ethical issues before a decision is made to proceed with a screening program.

Mandatory HIV screening has a very limited role in AIDS prevention and control programmes.

Routine screening of donors helps prevent the transmission of HIV through blood, semen, or other cells, tissues, and organs. Part of such screening is informed consent by the individual and consultations, which must be kept confidential.

The identification of seropositive individuals through a survey allows determining the epidemiological type of HIV, which is necessary to assess areas and populations in need of special educational programs or other preventive services. These surveys should be conducted using methods that do not threaten respect for human rights. They should be carried out during the consultation, either with the consent of an informed individual, while respecting confidentiality, or in an anonymous, free manner (without recording other personally identifiable data).

Voluntary AIDS testing can be part of health care for suspected HIV-related illnesses, and can be integrated with information, education, counseling and other support services to promote sustainable behavior change. In voluntary HIV testing, obtaining consent from an informed individual and being able to receive counseling while maintaining confidentiality are very important. Voluntary HIV testing services should be widely available as part of AIDS prevention and control programs and access to such services should be facilitated.

For early diagnosis, testing for HIV infection is used. Methods for diagnosing an infection are constantly being improved, since the main symptoms of the disease do not appear immediately, masquerading as other pathologies. Moreover, at laboratory research the percentage of both false-positive and false-negative results is high.

Test systems use blood to determine HIV, less often they use urine and scraping from the oral mucosa.

Stages of diagnosing HIV infection in adults:

Preliminary - screening that selects candidates at risk (presumably infected);

Reference

Confirming - expert stage.

From stage to stage, the complexity, labor intensity and cost of research methods are growing.

Terms used in the course of HIV diagnosis:

Antigen - HIV or its parts (capsule, enzymes, lipids, proteins).

An antibody is a cell of the immune system produced by the body against the introduction of a viral infection.

Seroconversion is an immune response of the defense system against the active reproduction of the virus. Immediately after entering the body, HIV cells begin to actively divide. In response, the concentration of antibodies rises for several weeks. When they reach a certain level (seroconversion), test systems are available for diagnosis. As the concentration of the virus falls, the level of antibodies falls.

"Window period" - the time interval from the moment of infection to the appearance of seroconversion, takes from 1.5 to 3 months. An infected person during this period is especially dangerous as a carrier of infection, since an HIV test shows a false negative result, although the risk of transmitting the disease is extremely high.

During screening, enzyme immunoassay (ELISA) is performed to determine the total antibodies to HIV-1 and HIV-2. It shows accurate results no earlier than 3-6 months after infection, although there are exceptions: it can detect antibodies to HIV 3-5 weeks after a dangerous contact.

Fourth generation test systems are the most accurate. In addition to antibodies to the virus, they are able to determine also the antigen to HIV (p-24-capsid), which makes it possible to detect the virus even in the “window period”, before the appearance of antibodies.

The high cost of such test systems forces in many countries to use systems of the third and even second generation, which determine only the presence of antibodies.

Such systems give false positive results under the following conditions:

Infection during pregnancy;

With a positive result of the enzyme immunoassay, they proceed to the next stage of diagnosis.

Reference step in HIV diagnosis

A double diagnosis is used with more sensitive test systems. Two positive results are a reason to move to the next level of diagnostics.

Expert stage - immunoblotting

At this stage, antibodies to individual proteins of the human immunodeficiency virus are determined.

Stages of the expert stage:

Destruction of the virus into individual antigens by electrophoresis.

Transfer of antigens using the blotting method onto special strips with pre-applied HIV-specific proteins.

Fixing the reaction that occurs if the patient's blood contains antibodies to antigens.

There is a small risk of error - a false negative result. It is possible if the study occurs in the terminal stage of the disease or in the "window period".

In combination with other tests, the PCR method (polymerase- chain reaction). He is different hypersensitivity to the virus, which can lead to a high proportion of false positive results.

Diagnosis in children whose mothers are HIV-infected

Testing of such children has its own characteristics - the mother's antibodies to HIV may be present in the child's blood, which crossed the placenta during childbirth. They can last up to 15-18 months from the birth of the baby. if there are no such antibodies, this is not one hundred percent proof that the child is not infected with the virus.

Screening - detection of the frequency of unrecognized morbidity using high-speed testons. As a rule, screening involves routine testing within the entire population or individual groups within the population. A serological test for the presence of antibodies to HIV in humans has become widely available since 1985. In the mass practice of testing and screening, enzyme immunoassay methods are most often used, which, however, can give both false positive and false negative results.

These tests were developed for the purpose of examining donated blood and therefore have such a high sensitivity that the probable error in their implementation gives a positive rather than a negative result. If the test result is positive, the donated blood must be destroyed. As for the donor himself, he undergoes control testing. False-negative test results primarily depend on the fact that the incubation period for HIV infection is 1-3 months (average 6 weeks). During this period, a person is already a virus carrier (and therefore contagious), which, however, an HIV antibody test does not reveal. Sometimes this “invisible period” (or, as it is also called, the “hidden period of virus circulation”) can be up to three years.

Clearly, screening the entire population for HIV will not be effective. Particularly where the prevalence of HIV infection is low, testing will produce more false positives. than truly positive results. It is also necessary to take into account the strongest stresses for imaginary seropositives, which sometimes lead to iatropsychogenias (a kind of neurosis), an increase in "speedophobia" moods in society, conflicts in communication, and finally - unreasonable waste of financial resources (one test costs about one dollar).

The opportunity to be tested for the presence of antibodies to HIV should be provided to everyone. In today's society, testing can be voluntary and compulsory. At extrandom anonymous testing the patient is registered under the number; at the same time, it is permissible to indicate demographic information (age, gender), but neither the surname nor the address of the subject is entered in the documents. At voluntary confidentialsocial testing information about the identity of the patient is reflected in his medical records, but the patient must be provided with guarantees of non-disclosure of information.

HIV testing must necessarily be accompanied by patient counseling both before and after testing. Adequate informing the patient sometimes becomes the best psychotherapy. Depending on the individual psychological characteristics of each patient, it is advisable to inform him that the medical literature has repeatedly reported cases where regular sexual activity with an HIV-infected partner for many years did not lead to infection; what are false-positive test results; that a positive result does not mean AIDS; that medicine knows cases when AIDS does not develop in "HIV-positive" people for more than 10 years, and so on.

The grossest violation of professional ethics will be a message to the patient about a positive test result that has not yet been confirmed in a reanalysis, not preceded by competent counseling. Patients are finally informed about the test results only after confirmation of positive test results. This is done in order to avoid tragic cases, such as the one that occurred in Riga in 1991: the spouses, having learned about a positive test result from one of them, committed suicide; post-mortem studies did not reveal the fact of HIV infection.

Problem mandatory testing and screening for HIV causes heated debate, in which scientific and epidemiological, moral and ethical, legal, socio-economic and even political aspects are intertwined. Many countries have adopted mandatory HIV screening of blood, semen, other donor tissues and organs. Since 1985, the United States has introduced mandatory testing in the army (2 million recruits, military personnel and reservists are subject to mandatory HIV testing annually). Some states require AIDS testing before marriage, and since 1997 New York State has introduced mandatory HIV testing of all newborns. and In the United States, there are many mandatory HIV testing regulations that set this country apart from the rest.

In Japan, it was not until 1994 that the Ministry of Labor recommended that employers abandon the mandatory testing requirement for employment. However, mandatory testing must be carried out by employees sent by companies to work in countries whose legislation requires foreigners to have a certificate of absence of HIV infection and AIDS. In these cases, the presence of a positive test result means that such an employee will not be sent abroad, however, the company management is obliged to guarantee that he retains a job inside the country.

In general, many foreign experts believe that the practice of mandatory HIV testing not only violates human rights, but also turns out to be ineffective as a barrier to the spread of the epidemic, and therefore its use should be rather limited. WHO also does not support the practice of mandatory testing.

In our country, mandatory reporting of AIDS cases was introduced in 19H5 from the moment the first case of the disease was detected (Sweden was the first country to adopt a law on mandatory notification of all cases of this disease in 1983). At the initial stage, the policy of combating AIDS in the USSR was almost entirely reduced to mandatory screening. Thus, in the Decree of the Presidium of the Supreme Soviet of the USSR "On Measures to Prevent Infection with the AIDS Virus" adopted in 1987, it was said that both citizens of the USSR and foreigners located on its territory could be required to undergo a medical examination for infection with the virus. AIDS. According to the Decree, knowingly placing another person in danger of contracting AIDS was punishable by imprisonment for a term of 5 years, and self-infection - for a term of up to 10 years.

The "Rules for Medical Examination for Detecting AIDS Virus Infection" issued by the USSR Ministry of Health on the basis of this Decree stated that the following are subject to examination: donors (of blood and other tissues); Soviet citizens who returned from foreign business trips lasting more than 1 month; foreigners who arrived in the USSR for for a period of more than 3 months from countries where AIDS is widespread: persons from "risk groups" (permanent recipients of donated blood, drug addicts, homosexuals and prostitutes); persons "who had contacts with patients or virus carriers" At the end of the list were named persons who expressed a desire undergo such an examination.

These documents sang a legal basis for the screening of donated blood for HIV, which had actually been carried out in the country since 1986, and the practice of medical epidemiological investigations, which for some time played a leading role in our country in detecting the spread of HIV infection. In both documents, attention is drawn to the norm that allowed the use of coercive measures against citizens who evade mandatory testing, directly by the health authorities or the police, without the participation of representatives of the prosecutor's office or the court. It is unlikely that intimidation of the population with criminal liability for "knowingly placing another person at risk of infection" had any other meaning than the self-satisfaction of medical officials who sought to create the impression among representatives of the highest authorities that they were taking effective measures to combat AIDS.

More realistic measures for such a struggle were taken by epidemiologists and clinicians themselves. So, on their initiative, in February 1987, the All-Union Radio announced the opening of an anonymous AIDS screening room in Moscow. A few days later, this office started working, accepting up to a thousand people a month.

Initiated in 1986 in our country, mandatory HIV screening of large contingents of the population has been steadily expanding. Moreover, contrary to the norms adopted by the USSR Ministry of Health, in some places, on the basis of decisions made at the local level, mandatory HIV testing of all patients admitted to hospitals (especially surgical ones) was introduced. As a result, more than 95 million HIV tests were carried out between 1987 and 1992. What was the effectiveness of such a large-scale practice? During routine examinations, about 29 million donors were not identified as infected; out of more than 27 million pregnant women tested, 30 were found to be infected; out of 2 million patients with venereal diseases - 58 infected; from almost 2 million prisoners - 3 infected, etc. An anonymous survey covered only 356,942 people and identified 13 HIV-infected people.

If one remembers that one test costs the health care budget one dollar, then there are serious doubts about the appropriateness of spending such significant funds on such ineffective interventions. It is well known that in most other countries the strategy to combat AIDS is different: appropriate education of the population, programs for training certain social groups in safe forms of behavior, every possible encouragement of people who have reason to worry about their health to undergo voluntary HIV testing, etc.

The foregoing does not at all mean a complete denial of the expediency of mandatory HIV testing for certain groups of the population.

A separate discussion deserves the so-called widely used in our country. "epidemiological investigation methodniya". An epidemiological investigation is the identification of the source of infection and each case of infection, if possible, the restoration of the entire "chain" of infection transmission and, at the same time, measures taken to prevent the spread of infection.

In our country, using the method of epidemiological investigation in the period from 1987 to 1989, up to 70% of all HIV-infected people were identified. It was thanks to the use of this method that nosocomial transmission of HIV infection was proven in southern Russia.

During this period, everyone who could have at least something to do with the spread of the infection was examined; a large amount of unique scientific material has been accumulated - sera and lymphocytes were obtained from almost all infected people, and samples were taken from many patients repeatedly, which is important for studying the variability of the virus.

In countries where HIV testing is largely voluntary, this would simply not be possible. It can be stated that in this case, domestic doctors successfully solved the most acute problem of public health - the focus of infection was localized within 10 months - and carried out a very important program of scientific research.

In the early 1990s, many medical professionals and representatives of social movements (already then public organizations began to form in our country that provide psychological and social support to HIV-infected people) realized the limitations of a strategy based on mandatory examination (mainly testing) huge masses of the population. The principle of voluntariness of testing began to pay more and more attention, and not only because "it is accepted in civilized countries", but also because of the attractiveness of the principle itself for both patients and doctors.

As a result, the Federal Law “On Preventing the Spread and the Russian Federation of the Disease Caused by the Human Immunodeficiency Virus (HIV) Infection” adopted in 1995 requires mandatory testing for AIDS of “partners” 1 The obligatory prophylactic observation of HIV-infected people in health care institutions was also abolished.According to this Law, a medical examination for HIV infection is carried out voluntarily, and anonymously at the request of the examined person.Only blood donors are subject to mandatory testing for AIDS , biological fluids, organs and tissues, as well as representatives of certain professions (primarily doctors).

Diagnosis of HIV is one of the primary tasks that the employees of the dermatovenerological dispensary, as well as the staff of the polyclinic, face.

The disease is characterized by doctors as very insidious. It is characterized by a chronic course and is not amenable to full treatment. It is important to detect it in a timely manner in order to take it under control and prevent uncontrolled spread. What are the features of the human immunodeficiency virus, and how they can get infected, patients are often interested.

What are the methods of diagnosing the disease, and what signs make it possible to suspect infection?

Today, from everywhere you can hear about how dangerous HIV infection is. However, few people explain what this danger is. As a result, patients have an incomplete set of information and, as a result, do not take the threat seriously. But HIV is extremely dangerous. It is classified as a slowly progressive viral diseases prone to chronic course. In this pathology, the immune system is primarily affected.

Doctors draw the attention of patients to the fact that death does not occur from the immunodeficiency virus itself, as such.

A person dies from concomitant infections, to provide full protection against which the body is no longer able. Also, cancerous tumors become the cause of death, with which reduced immunity is unable to fight.

In fact, the mechanism of action of HIV infection on immune system pretty complicated. According to doctors, patients do not need to understand it thoroughly. It is enough to know that the disease can reduce the level of immunity to critical values. As a result, the body will be unable to defend itself against various external influences, which will lead to death sooner or later.

How infection occurs

It is important to understand that HIV infection today is surrounded by a wide variety of myths.

Patients are very ill-informed about when it is possible to become infected, and when health is out of danger.

The first thing to remember is that HIV is highly volatile in environment. This means that a pathogenic microorganism is able to live fully and for a long time only in human body. He does not tolerate heating above 50 degrees (dies instantly). Also not able to resist drying processes. Not all body fluids contain enough virus for infection to occur.

The greatest danger is:

blood;
pre-cum;
sperm;
discharge from the female vagina;
lymph;
breast milk.

If any of these fluids come into contact with mucous membranes in which there are microtraumas, or with skin affected by injuries, infection occurs.

It is also possible if the foreign fluid enters directly into the bloodstream. Saliva and tears, contrary to popular belief, do not pose a threat. Due to the characteristics of the virus and its low survival rate, it is transmitted in several ways:

sexual way i.e. with unprotected sexual intercourse, which inevitably entails the contact of biological fluids and mucous membranes of the body susceptible to the pathogen;
parenteral route i.e. transmission of the virus with blood during its transfusion or due to the use of non-sterile instruments for medical purposes;
vertical path i.e. from mother to child (today, if a woman takes antiretroviral therapy and refuses to breastfeed, the likelihood of infection of a child during childbirth is minimized).

It is important to understand that if microtrauma or open wounds are required for infection through the skin, then this is not a necessary condition for infection through the mucous membrane. The difference is explained by the fact that the mucous membranes and skin human body have completely different structures. This difference must be taken into account.

How to suspect HIV

Many patients are interested in the question of what signs can usually be used to suspect infection with the human immunodeficiency virus.

unreasonable increase in temperature of the systemic type, which cannot be explained by any other infection, and which persists for a long time, despite the measures taken for treatment;
strong increase lymph nodes in size (in the first place, nodes in the groin area suffer, but their involvement throughout the body is also possible);

severe weight loss that cannot be explained by diets, stress, hormonal disruptions and other reasons;
complaints of stool disorders that haunt the patient for a long time, and it is not possible to find the reason why they appeared;
a pronounced tendency to move any infectious diseases in chronic forms, and the nature of the pathogen does not matter much, both bacterial and viral pathologies are chronicled;
diseases provoked by opportunistic microflora develop, which does not pose a threat to a person whose immunity is fully functional (for example, mycoplasmosis, ureaplasmosis, candidiasis, etc.).

The clinic of HIV infection is very non-specific, as doctors say. Because of this, it is often difficult to make a diagnosis. Many patients completely ignore the alarming symptoms, preferring not to seek medical help. Even if the disease greatly affects their general well-being.

It is important to understand that HIV infection for a long time may not make itself felt at all. And when the first signs appear, a person may not even associate them with the possibility of his infection and make attempts to be treated at home.

Diagnostic methods

Laboratory diagnosis of HIV has been developed for a long time and has been successfully used to diagnose this dangerous disease.

The disease cannot be identified by symptoms alone. Therefore, confirmation of the diagnosis on the basis of laboratory methods often plays a decisive role.

Exist various methods HIV diagnosis. In Russia, first of all, preference is given to immune blotting, as well as ELISA reactions. These methods are often used as screening methods, for example, when checking medical personnel.

ELISA systems

Often, patients ask their doctors how to start a diagnostic search for suspected infection with the human immunodeficiency virus.

Any competent doctor will say that preference should be given to enzyme immunoassay. It is this technique in Russia that is the first diagnostic stage.

The principle of ELISA is simple. Doctors created special proteins in the laboratory. They are able to detect and interact with antibodies produced by the body in response to exposure to HIV. Then a special indicator enzyme is added to the system, which changes its color. At the final stage, the material is processed using a special apparatus, and the doctor receives the final result.

IFA is very popular.

First of all, due to the fact that you can get results even if no more than a few weeks have passed since the introduction of the pathogen into the body.

It is important to understand that enzyme immunoassay does not determine the virus itself in the blood, but antibodies to it.

For many people, they may begin to develop later than two weeks, which may cause the result to be erroneous. There are several generations of ELISA tests.

The most modern and high-precision are those that belong to the 3rd and 4th generations. Doctors note that it is best, if there is a choice, to give preference to European reagents, since their accuracy reaches 99%. The terms for obtaining the results of the ELISA are on average from 2 to 10 days.

Why ELISA can be false

It is important to understand that enzyme immunoassay can give both false positive and false negative results. Although the risk of such a development of events is extremely small.

The patient can get false negative results if the test was taken too early and antibodies have not yet formed in the body.

To exclude such a reaction, patients are advised to take the analysis several times with different intervals of time.

A false positive test occurs in some diseases. For example, patients with:

alcoholic hepatitis;
myeloma in large numbers;
some autoimmune diseases;
women during pregnancy, etc.

In such diseases, human blood is replenished with antibodies. They can resemble HIV antibodies in structure, which confuses the reagents, provoking a reaction. Of course, in last years test systems are becoming more and more sensitive. However, the problem of false results has not yet been fully resolved.

Immunoblotting

In modern conditions, it is impossible to make a positive diagnosis of HIV, relying only on ELISA. It is necessary to confirm the results obtained, which is performed using the reaction immune blotting(immunoblotting, IB).

To perform IB, special test strips must be present in the laboratory. They are coated with viral proteins. Before analysis, the patient's blood taken from a vein is prepared in a special way.

The resulting biological material is added to the gel, in which proteins are separated by their weight. Then, a pre-prepared strip is lowered into the resulting mass.

The band gets wet (blotting occurs), bands are detected on it if the material contains HIV infection proteins. If proteins are absent, wetting does not change appearance stripes.

There are several interpretations of immunoblotting. However, by whatever method a particular hospital or laboratory performs the decoding, the probability of correct diagnosis is 99.9%.

Can immunoblotting give incorrect results, patients often wonder? Yes, it is possible, for example, if a patient has tuberculosis, is pregnant, or suffers from oncology.

PCR to help

PCR is another method that can diagnose human immunodeficiency virus in blood and other body fluids where its concentration is quite high.

According to doctors, the polymerase chain reaction can give a positive result as early as 10 days after the first contact of the body with the infection.

It is important to understand that PCR in some cases gives false positive results. This is explained by the fact that the method has a very high sensitivity.

As a result, it often reacts to similar antibodies, indicating completely different pathological processes in the patient's body.

Despite its high sensitivity and low probability of false results, PCR is not widely used. This is explained by several factors. Firstly, to perform a polymerase chain reaction, special equipment is required, the price of which is quite high. Secondly, the personnel working with the equipment must be highly qualified, which can also cause difficulties. These features combined make PCR an expensive diagnostic method and, as a result, not accessible to everyone.

Despite the fact that PCR is not a screening method, it is used, for example, to test a newborn for infection with the human immunodeficiency virus.

Express systems for diagnostics

Doctors and scientists have spent a lot of effort to create rapid tests to assess HIV infection. According to doctors, when using these systems, it is possible to get a result within 15 minutes after the test has been carried out.

Rapid HIV tests are based on the principle of immunochromatography. The system usually includes a strip impregnated with special reagents.

The task of the patient is to apply blood, semen or any other biological fluid that may contain antibodies to the virus.

If they are found, then two colored bands will appear on the strip, one of which is control, and the other is diagnostic. If not detected, then only the control band will be detected.

It is important to understand that rapid tests do not give a 100% guarantee that a person is not infected or, on the contrary, is infected with HIV. In any case, the results obtained with their help must be confirmed in the laboratory using immunoblotting.

Express-type test systems are convenient for patients who want to calm themselves at home. However, as doctors note, even if with their help a person received a negative result, if you suspect negative changes in the body, you should still consult a doctor.

Which doctor should I contact if I suspect an infection?

Many patients are wondering which doctor they should contact if they suspect HIV infection. First of all, it is recommended to visit a venereologist. It is this medical worker specialize in diseases that can be transmitted from person to person sexually.

The venereologist will be able to conduct a competent examination, collect an anamnesis and decide what examinations the patient needs for an accurate diagnosis. At his discretion, he can also refer the patient to the infectious diseases hospital. Especially if he still suspects he has HIV.

The human immunodeficiency virus is a common disease. Any person leading an active sex life can face it.

Knowledge of the features of the spread and diagnosis of this disease in modern realities is vital if the patient wants to maintain his health and longevity. Only a timely appeal to the doctor will allow you to take the infection under control and protect yourself from it!