Epidemiology of tuberculosis

Epidemiology of tuberculosis is a section of phthisiology that studies the sources of tuberculosis infection, routes of transmission of infection, the prevalence of tuberculosis as an infectious disease among the population, unfavorable exogenous and endogenous factors influencing the epidemic process, and the population groups most at risk of developing tuberculosis.

An epidemic is a mass spread of an infectious human disease in a locality, significantly exceeding the usual level of morbidity (5-6 times). According to the rate of increase in morbidity, explosive epidemics and long-term epidemic processes with a slow (over many years) rise and a slow decline are distinguished. The latter includes tuberculosis.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ]

Routes of tuberculosis transmission

Integral parts of the epidemic process are the reservoir of tuberculosis infection, its source, susceptible population and routes of transmission of infection.

The tuberculosis infection reservoir consists of people infected with mycobacteria tuberculosis, some of whom become ill during their lifetime. Some animals are also considered a tuberculosis reservoir. The reservoir consists of two parts: potential (infected but not sick people) and active (identified and undetected patients with active tuberculosis).

The source of tuberculosis is people and animals sick with tuberculosis, releasing mycobacterium tuberculosis into the environment.

Susceptible population - people infected with Mycobacterium tuberculosis, susceptible to tuberculosis.

Since tuberculosis mycobacteria are resistant to the effects of many environmental factors and persist for a long time in various substances (liquid and dry sputum, other secretions of patients, food products, etc.), infection with tuberculosis occurs in various ways.

• Airborne is the main route of infection. In this case, the smallest droplets of sputum containing tuberculosis mycobacteria penetrate the alveoli. The most dangerous are patients with massive bacterial excretion, who even during normal conversation disperse infected droplets of sputum. Aerosol also spreads with strong coughing, sneezing, and loud talking. Sprayed aerosol (the smallest infected droplets of sputum up to 5 microns in size) remains in the air of a closed room for up to 60 minutes, and then settles on furniture, floors, walls, clothes, linens, food products, etc. The best conditions for infection are poorly ventilated closed rooms where a coughing patient is located.
• Infection by airborne dust occurs when inhaling dust particles containing mycobacteria, for example when shaking out clothes, linens and bedding of bacteria-carrying individuals in a room.
• The alimentary route of infection is possible when eating products contaminated with mycobacteria. Among animals, more than 50 species of mammals and the same number of bird species are known to be susceptible to tuberculosis. Among these animals, cows and goats can be involved in infecting humans. Infection occurs when bovine mycobacteria are transmitted through milk and dairy products, much less often when eating meat or through direct contact with animals. Tuberculosis in dogs, cats, sheep, and pigs is of no serious epidemiological significance.
• The contact route of infection through the skin and mucous membranes can be observed in persons directly working with the culture of Mycobacterium tuberculosis or infectious material (for example, pathologists, laboratory workers). Livestock workers can also become infected in this way when in contact with a sick animal.
• Intrauterine infection (extremely rare) is possible when the placental barrier is damaged or as a result of swallowing amniotic fluid containing mycobacteria. At present, this route of infection transmission has no serious epidemiological significance.

Tuberculosis infection and disease

Tuberculosis is an infectious disease with a long period between infection (contamination) and the development of the disease. After a person comes into contact with a bacteria carrier or infected material, there is a possibility of infecting a healthy person, which depends on the properties of the pathogen, as well as on the susceptibility of the human body. One bacteria carrier can infect an average of 10 people per year. The probability of infection increases in the following situations:

• upon contact with a patient with tuberculosis with massive bacterial excretion;
• in case of prolonged contact with a carrier of bacteria (living in a family, being in a closed institution, professional contact, etc.);
• in close contact with a carrier of bacteria (being in the same room with a sick person, in a closed group).

After infection with mycobacteria, clinically expressed disease may develop. The probability of developing the disease in a healthy infected person throughout life is about 10%. The development of tuberculosis depends primarily on the state of the human immune system (endogenous factors), as well as on repeated contact with mycobacteria tuberculosis (exogenous superinfection). The probability of developing the disease increases in the following situations:

• in the first years after infection:
• during puberty;
• in case of re-infection with Mycobacterium tuberculosis:
• in the presence of HIV infection (the probability increases to 8-10% per year);
• in the presence of concomitant diseases (diabetes mellitus, etc.):
• during therapy with glucocorticoids and immunosuppressants.

Tuberculosis is not only a medical and biological problem, but also a social one. Psychological comfort, socio-political stability, material standard of living, sanitary literacy, general culture of the population, housing conditions, availability of qualified medical care, etc. are of great importance in the development of the disease.

The role of primary infection, endogenous reactivation and exogenous superinfection

Primary tuberculosis infection occurs when a person is initially infected. As a rule, this causes adequate specific immunity and does not lead to the development of the disease.

In case of exogenous superinfection, repeated penetration of tuberculosis mycobacteria into the body and their reproduction are possible.

With close and prolonged contact with a bacteria carrier, mycobacteria tuberculosis repeatedly and in large quantities enter the body. In the absence of specific immunity, early massive superinfection (or constant re-infection) often causes the development of acutely progressive generalized tuberculosis.

Even in the presence of specific immunity developed after the primary infection, late superinfection can also contribute to the development of the disease. In addition, exogenous superinfection can contribute to the exacerbation and progression of the process in a patient with tuberculosis.

Endogenous reactivation of tuberculosis occurs from primary or secondary foci in organs that have remained active or have become aggravated. Possible causes are decreased immunity due to background or aggravated concomitant diseases. HIV infections, stressful situations, malnutrition, changes in living conditions, etc. Endogenous reactivation is possible in the following categories of people:

• in an infected person who has never previously had any signs of active tuberculosis:
• in a person who has had active tuberculosis and is clinically cured (once infected, a person retains tuberculosis mycobacteria in the body for life, i.e. biological cure is impossible);
• in a patient with a dying down tuberculosis process.

The possibility of endogenous reactivation in infected individuals allows tuberculosis to maintain a reservoir of infection even with clinical cure of all contagious and non-contagious patients.

Control over the tuberculosis epidemic process

The presence of tuberculosis patients with bacterial excretion (both identified and undetected) allows for the reproduction of new cases of the disease to continue. Even if bacterial excretors are cured, the reservoir of tuberculosis infection will persist as long as there is a significant number of infected individuals in the population who have the potential to become ill with tuberculosis due to endogenous reactivation. Therefore, it will be possible to talk about defeating tuberculosis only when a new, uninfected generation of people grows up. In this regard, health-improving preventive measures among the entire population with an emphasis on risk groups are especially important.

The goal of anti-tuberculosis work is to establish control over the tuberculosis epidemic process, which will entail a decrease in the true incidence, mortality and prevalence of tuberculosis. To do this, it is necessary to carry out a set of measures aimed at reducing the number of infection sources, blocking transmission routes, reducing the reservoir and increasing the population's immunity to infection.

[ 6 ], [ 7 ], [ 8 ], [ 9 ], [ 10 ]

Measures to reduce the number of sources of tuberculosis

• Identification of tuberculosis patients by all available methods - with the help of mass preventive examinations of the population, as well as examination when visiting a doctor of any specialty of patients with symptoms suspicious for tuberculosis. Increasing the coverage and improving the quality of preventive examinations, as a rule, leads to a short-term increase in the incidence rate.
• Clinical cure of the overwhelming majority of tuberculosis patients (newly diagnosed individuals and patients from contingents of anti-tuberculosis institutions). This is possible only with the use of a comprehensive approach to treatment (controlled chemotherapy, pathogenetic therapy, collapse therapy, surgical treatment, sanatorium treatment, etc., if indicated), as well as the establishment of an adequate sanitary and hygienic regime.

Measures to prevent transmission of tuberculosis

• Hospitalization of bacteria excretors in an anti-tuberculosis hospital until massive bacterial excretion ceases.
• Implementation of measures to limit the spread of infection in anti-tuberculosis institutions (administrative measures, environmental monitoring, use of personal protective equipment).
• Conducting anti-epidemic measures (current and final disinfection, chemoprophylaxis of contacts, etc.) in tuberculosis infection foci (in places where patients stay, in any medical institutions where a patient with tuberculosis has been identified, in anti-tuberculosis service institutions).

Measures to reduce the reservoir of tuberculosis and increase the population's immunity to the disease

Sent to work with infected and uninfected populations.

• Prevention of recurrent cases of tuberculosis among recovered individuals through a range of preventive measures (health-improving procedures, spa treatment, anti-relapse courses of therapy).
• Conducting preventive anti-tuberculosis immunization of the population.
• Improving the standard of living of the population, improving housing and living conditions, increasing health literacy, general culture, etc.

Indicators characterizing the epidemic process

The main objective of the analysis of the epidemic process is to clarify the nature and intensity of the spread of tuberculosis infection, identify sources of infection, routes of transmission of the pathogen and determine priority areas of a set of anti-epidemic measures.

The analysis of the epidemic situation is carried out according to intensive indicators describing the spread of the phenomenon. The main intensive indicators characterizing the tuberculosis epidemic process are mortality, morbidity, morbidity (prevalence) and infection.

Extensive indicators are used to characterize the structure of the phenomenon being studied (for example, the proportion of a given clinical form of tuberculosis among all forms).

Absolute values should be taken into account when planning the volume of anti-tuberculosis measures (the workload of doctors, calculating the need for drugs, planning the number and profile of beds, etc.).

The visibility indicators reflect changes in the epidemiological situation. The indicator of the initial (or base) year is taken as 100%, and the indicators of subsequent years are calculated in relation to them.

It is important to understand that only the interaction between indicators can more likely characterize a particular epidemic situation in a region and be an indirect reflection of the level of organization of anti-tuberculosis care for the population.

Mortality from tuberculosis is a statistical indicator expressed as the ratio of the number of deaths from tuberculosis to the average annual population in a specific administrative territory for a certain period of time (for example, during the reporting year).

When analyzing the tuberculosis mortality rate, it is important to determine the proportion of patients identified posthumously and the proportion of patients who died in the first year of observation. An increase in the tuberculosis mortality rate is the most objective criterion for the unfavorable state of the epidemic process.

The tuberculosis incidence rate, or detection rate, is the number of tuberculosis patients newly identified and registered in a specific administrative territory over a certain period of time (e.g., during the reporting year). The incidence rate also includes the number of people diagnosed with tuberculosis posthumously.

It is necessary to distinguish between the incidence rate of tuberculosis and the true incidence rate in an administrative territory.

The incidence rate reflects only cases of the disease that are identified and officially registered and directly depends on the following factors:

• the coverage and quality of preventive examinations of the population for tuberculosis;
• organization and quality of examination of a patient when visiting a doctor with symptoms suspicious of tuberculosis;
• level of registration of identified cases;
• the level of true tuberculosis incidence.

In practical work, a phthisiologist-healthcare organizer has to evaluate the quality of the general medical network in identifying tuberculosis patients. If the coverage of the population with preventive examinations in an administrative territory is low, it is possible to approximately calculate the number of under-identified patients in the previous year. To do this, it is necessary to know the number of people in whom the disease was identified extremely late, which, as a rule, include the following cases:

• newly diagnosed patients with fibrocavernous tuberculosis;
• persons identified posthumously;
• persons who died from tuberculosis in the first year after detection.

When calculating the mortality rate from tuberculosis in the Russian Federation, mortality from the consequences of tuberculosis is also taken into account. However, the total number of such persons is small and does not have a significant impact on the mortality rate.

The calculation of the incidence rate in the Russian Federation differs from the calculation by WHO. WHO calculates the incidence rate for all countries, including the number of newly diagnosed patients and relapses of tuberculosis. The WHO European Office also includes a group of patients with an unknown anamnesis in the incidence rate.

Morbidity (prevalence, patient cohorts) is a statistical indicator reflecting the relative number of patients with active tuberculosis (newly diagnosed, relapses, after early termination of chemotherapy, after an ineffective chemotherapy course, chronic patients, etc.) registered in the I and II GDUs at the end of the reporting year in the administrative territory.

The infection rate of the population with Mycobacterium tuberculosis is determined by the percentage ratio of the number of people with a positive Mantoux test with 2 TE (excluding people with post-vaccination allergies) to the number of those examined.

In conditions of total vaccination of newborns and revaccination (taking into account the difficulties in differential diagnostics between infectious and post-vaccination allergy) the use of the infection rate indicator may be difficult. Therefore, an indicator is used that characterizes the annual risk of infection - the percentage of the population exposed to primary infection with tuberculosis mycobacteria.

To assess the tuberculosis epidemic situation, indicators characterizing the level of organization of anti-tuberculosis care for the population are also used. The main ones are the coverage of the population with preventive examinations for tuberculosis, the effectiveness of treating patients, as well as indicators characterizing the effectiveness of preventive measures in the infection focus.

The list of persons listed and the approach to calculating the indicator are not final and indisputable. For example, patients with cirrhotic tuberculosis are also classified as late-diagnosed patients. In addition, some patients who died in the first year of observation and were identified posthumously may die not from late detection of advanced tuberculosis, but from acute progression of the process. Nevertheless, information on the persons listed in the text is available, they are calculated and monitored annually, and they can be obtained from approved statistical reporting forms.

Factors that increase the risk of developing tuberculosis

The phenomenon of "selectivity" of tuberculosis in people infected with Mycobacterium tuberculosis has long attracted the interest of researchers and prompted them to search for the causes that contribute to the development of the disease. Retrospective analysis of the spread of tuberculosis infection inevitably leads to the conclusion that the "earliest" in origin and most significant in terms of impact are migration, demographic and social factors. This can be confirmed by:

• the epidemic nature of the spread of tuberculosis during the development of urbanization processes (starting from the Middle Ages in Europe);
• the predominant spread of tuberculosis among the poorest strata of the urban population living in crowded and unsanitary conditions;
• an increase in the prevalence of tuberculosis during periods of military action, socio-economic and demographic upheavals.

The general mechanism of rapid spread of tuberculosis in these conditions can be considered to be an increase in the number of close contacts of healthy individuals with tuberculosis patients (i.e. with sources of tuberculosis infection). An important factor is also a decrease in the general resistance of the body in most individuals who are under conditions of prolonged stress, malnutrition and unfavorable living conditions. At the same time, even in extremely unfavorable living conditions and in the presence of close contact with patients excreting tuberculosis mycobacteria, tuberculosis did not develop in a certain category of individuals for a long time. This indicates a different degree of genetically determined individual resistance to tuberculosis. It should be recognized that the factual material currently available does not allow the formation of risk groups for tuberculosis based on the study of the genetic characteristics of various individuals.

A huge number of studies (most of them conducted in the second half of the 20th century) are devoted to the analysis of endogenous and exogenous factors or their combinations that increase the risk of tuberculosis. The methodology and ideology of these studies are so dissimilar, and the results obtained are so contradictory (and sometimes diametrically opposed) that at present, with a sufficient degree of certainty, we can only speak of the presence of three main groups of factors that determine the increased risk of tuberculosis:

• close contact with people sick with tuberculosis (household and industrial);
• various diseases and conditions that reduce the body's resistance and create conditions for the development of tuberculosis;
• socio-economic, everyday, environmental, industrial and other factors.

The above factors can influence both the various phases of the epidemiological process and the pathogenesis of the development of clinical forms of tuberculosis in an individual, micro-, macro-society or population (society).

This influence is carried out in a certain sequence:

• infection;
• latent (subclinical) infection;
• clinically manifest form of the disease:
• cure, death or chronic ongoing form of the disease.

Most studies on identifying risk groups for tuberculosis have been based on retrospective studies of cases. Nowhere has the probability of an individual with one or more risk factors being diagnosed throughout life been tracked. The role of a particular risk group in the overall incidence of tuberculosis has also been insufficiently assessed. In some cases, it is not that significant. For example, contacts of tuberculosis patients in 2005 accounted for only 2.8% of all newly diagnosed tuberculosis patients. In addition, various combinations of several risk factors are possible, which is extremely difficult to take into account in statistical studies. The same disease has a different effect on the overall resistance of the body not only in different people, but also in one individual, depending on the presence and combination of many endogenous and exogenous factors.

In Russia, high-risk groups for tuberculosis are identified based on medical and social characteristics, which is reflected in current regulatory and instructional documents. However, the combination of these factors and the significance of each of them are very dynamic and uneven even in stable territorial entities. Given the social, ethnic and demographic diversity of Russia, defining the general characteristics of "risk groups" for tuberculosis is a serious scientific, organizational and practical problem. Experience in individual territories shows that by forming "risk groups" taking into account regional specifics, it is possible to significantly increase the effectiveness of examination and the efficiency of tuberculosis prevention among these population groups. Thus, a study conducted in the Tula Region in the 1990s made it possible to develop and implement a differentiated scheme for examining population groups with varying degrees of risk for tuberculosis. As a result, it became possible to identify 87.9% of tuberculosis patients by reducing the volume of fluorographic examinations to 58.7%. The results of other studies indicate that increasing the coverage of risk groups with preventive examinations by 10% allows identifying 1.6 times more patients among them. Consequently, in modern conditions, preventive examinations for tuberculosis should be not so much mass as group and differentiated, depending on the risk of the disease or the epidemic danger of each group.

There is also no doubt that homeless people, immigrants and refugees are included in the high-risk group for tuberculosis. Obtaining reliable information on the incidence rate of these groups is complicated by the complexity of their accounting, registration and preventive examinations. Therefore, along with identifying this risk group, it is also necessary to develop interdepartmental measures (with the participation of the general medical network, the Ministry of Internal Affairs and other departments) to involve them in examination.

For several decades, various pathological conditions, acute and chronic infectious and somatic diseases have been considered factors of increased risk of tuberculosis. The structure and number of these "risk groups" in individual regions may have significant differences, which is associated with both real regional characteristics and the quality of work of medical institutions in identifying people with various diseases, their examination, treatment and dispensary observation. The general trend of recent years is a significant increase in the number of people with HIV infection; these contingents are the group with the highest risk of tuberculosis. The methodology for monitoring, identifying and preventing tuberculosis among HIV-infected individuals is very labor-intensive and differs in many ways from the measures carried out in other risk groups.

Thus, there are quite a large number of factors (social, industrial, somatic, etc.), the adverse impact of which increases the risk of tuberculosis for both individuals and population groups (often too numerous). The degree of negative impact of each of these factors varies in individual regions and changes dynamically over time. This circumstance makes it relevant to analyze and monitor the incidence of tuberculosis in various population groups, identifying risk factors characteristic of a specific region in a certain period of time.

At present, the Government of the Russian Federation Resolution No. 892 of 25.12.2001 "On the implementation of the Federal Law "On the prevention of the spread of tuberculosis in the Russian Federation" defines population groups that are subject to additional examination and monitoring in order to detect tuberculosis. These include both individuals from risk groups for tuberculosis or its relapse, and those whose tuberculosis can lead to massive contact with infection of a large group of people, including those particularly susceptible to tuberculosis (newborns, children, etc.). It should be noted that the identification and examination of risk groups does not mean the cessation of mass preventive examinations of the population - another thing is that the examination of risk groups should be close to 100% with full compliance with the frequency of examination, which, unfortunately, is not done everywhere.

At present, it has not been determined in which epidemic situation it is necessary to examine the entire population, and in which - mainly risk groups. In those subjects of the Russian Federation where the incidence rate of tuberculosis over the past few years is higher than 100 per 100 thousand of the population, and the coverage of preventive examinations of the population is lower than 50%, where the mortality rate from tuberculosis is also increasing, it is necessary to decide on preventive examination of the entire population with a frequency of at least once a year.

In more favorable epidemiological conditions, with constant good coverage of the population with preventive examinations, decreasing mortality rates from tuberculosis, where the incidence rate also tends to decrease, it is possible to switch to preventive examination mainly of risk groups for tuberculosis.

[ 11 ], [ 12 ], [ 13 ], [ 14 ]

The global tuberculosis epidemic

Tuberculosis is the "oldest" of the infectious diseases known to mankind. It can be stated with a high degree of probability that Mycobacterium tuberculosis as a biological species is significantly older than the species Homo sapiens. Most likely, Mycobacterium tuberculosis was initially predominantly distributed in southern Europe, Asia and northern Africa.

The discovery of America and Australia by Europeans, their advance into Africa, and the expansion of contacts with Europeans in Japan led to the widespread spread of tuberculosis mycobacteria and, as a consequence, to mass tuberculosis among the indigenous population of these territories. Retrospective analysis suggests that ethnic groups that have had long-term interaction with tuberculosis mycobacteria gradually increase the number of people resistant (or relatively resistant) to tuberculosis in their population. That is why, for a significant portion of the European superethnos, which has a centuries-old history of fighting tuberculosis, tuberculosis mycobacteria are currently weakly pathogenic, since no more than 10% of all infected people become ill. At the same time, among ethnic groups whose contact with tuberculosis mycobacteria began after a relatively recent encounter with Europeans, the incidence of tuberculosis is extremely high and still represents not only a social but also a biological problem. An example of this is the extremely high prevalence of tuberculosis among American Indians in Latin America, among the indigenous population of Australia and Oceania.

It is quite difficult to judge the true prevalence of tuberculosis not only because of the unequal (and sometimes incomparable and unreliable) statistical data. Different countries still have different approaches to diagnosing tuberculosis and verifying the diagnosis, defining a case of the disease, registering it, etc. In connection with the above, many researchers, when retrospectively analyzing the dynamics of the epidemic situation for tuberculosis, give preference to the mortality rate, quite rightly emphasizing its informativeness and objectivity compared to other indicators.

The first statistical data on mortality from tuberculosis date back to the end of the 17th century and the first half of the 18th century. At that time, they concerned only individual cities in Europe. This is quite natural for at least two reasons. Firstly, the problem of the mass spread of tuberculosis became one of the priorities for humanity precisely due to the development of cities, where close contact (and, consequently, infection) between the healthy population and those sick with tuberculosis occurred. Secondly, it was in cities that the level of development of medicine made it possible to organize such studies and document their results.

The data presented show that in the 17th, 18th and first half of the 19th centuries tuberculosis was a widespread and progressive epidemic that took a large number of human lives. It should not be forgotten that during this period the population of Europe also suffered severely from other infectious diseases: smallpox, typhus and typhoid fever, syphilis, diphtheria, scarlet fever, etc. The "contribution" of tuberculosis as a cause of mortality of the population looks even more significant. Thus, in London in 1669 the extensive mortality rate from tuberculosis was 16%, in 1741 - 19%, in 1799 - 26.3%, and in 1808 - 28%. The proportion of tuberculosis among the causes of death in Plymouth was close to these figures (23%), and in Breslau even 40%. In Vienna from 1648 to 1669, tuberculosis was the cause of death for 31% of the local Jewish population.

The 20th century was characterized by the most rapid dynamics of tuberculosis prevalence. This is due to the fact that it was at the turn of the 19th and 20th centuries that humanity first acquired “tools” for active influence on tuberculosis. R. Koch’s discovery of the tuberculosis mycobacterium made it possible to study the characteristics of the pathogen, which was initially used to develop bacteriological diagnostic methods and tuberculin diagnostics, and then to create a specific vaccine. The use of V.K. Roentgen’s discovery and the mass introduction of radiation research methods into practice was the second revolutionary contribution to the development of phthisiology. Thanks to the X-ray research method, clinicians significantly expanded their understanding of the nature and characteristics of the tuberculosis process and, most importantly, for the first time were able to diagnose the disease before the onset of its clinical manifestations.

The progressive development of medicine, biological sciences and a number of related specialties, the integration of specialties and the use of the achievements of scientific and technological progress made it inevitable to solve a problem that seemed insoluble to many generations of doctors and patients - the development and implementation of specific anti-tuberculosis drugs. The contribution of surgical methods of treatment, the development and application of which in the 20th century saved the lives of hundreds of thousands of tuberculosis patients, should not be underestimated. Epidemiology, the development and implementation of a system of organizational measures, the creation of a methodology for recording, statistics, and then monitoring tuberculosis also contributed to the fight against tuberculosis.

The availability of sufficiently reliable factual data allows us to conduct a retrospective analysis of the patterns and dynamics of the tuberculosis epidemic in the 20th century. By the beginning of the 20th century, tuberculosis remained a widespread disease. In 1900, for example, 473 people per 100 thousand inhabitants died in Paris, 379 in Vienna, 311 in Stockholm, etc. Against the background of economic growth before the First World War, a decrease in mortality from tuberculosis was observed in some countries (England, Germany, Denmark. Netherlands. USA) or stabilization of this indicator (Austria, Norway, Finland, France).

The economic and social upheavals associated with the First World War caused a significant increase in tuberculosis mortality in all European countries. Its rise was already noted by the end of the first year of the war, and later this indicator had a clear upward trend in England, Austria, Germany, Italy and Czechoslovakia. In Austria in 1918, the tuberculosis mortality rate exceeded the pre-war level by 56%, and in Germany by 62%. Mortality among the population of large cities (London, Berlin, Vienna) increased at an accelerated rate. In Warsaw, mortality increased almost threefold by 1916.

During the First World War, some peculiarities of the course of tuberculosis were noted among different age groups of the population. Young children suffered the least, while older children and the young population (15 to 30 years) suffered the most. In most countries, the differences in mortality rates between men and women typical of peacetime were preserved. Thus, higher figures among men in England were observed throughout the war. The inverse ratio that took place in Switzerland and the Netherlands during peacetime did not change in 1915-1917. After the end of the First World War, against the backdrop of economic recovery and stabilization of the social sphere, mortality from tuberculosis decreased to one degree or another in most European countries, Australia, New Zealand and the USA.

During the Second World War, mortality increased again in the countries occupied by the German army, in Germany itself and in Japan. Mortality from tuberculosis in many countries and in large cities steadily increased as military actions continued. In 1941-1945, it exceeded the pre-war level among residents of Amsterdam, Brussels, Vienna, Rome, Budapest by 2-2.5 times, and in Berlin and Warsaw - by 3-4 times.

It should be noted that the data provided concerned only the civilian population; they did not include the huge number of people who died from tuberculosis in the army, captivity, and concentration camps. Meanwhile, among prisoners of war released from concentration camps and sent to Sweden, 40 to 50% were sick with tuberculosis. At the same time, in most countries that did not participate in World War II (for example, Sweden and Switzerland), the mortality rate continued to decline. This indicator was stable in Canada and the United States, which did not actively participate in the hostilities. Thus, the sanitary consequences of World War II in relation to tuberculosis were not the same in different countries. To a large extent, this depended on the degree of destruction of the material and technical base and economic ties, the overcrowding of the majority of the population, the high intensity and partial uncontrollability of migration processes, mass violations of sanitary standards, disorganization of the medical and sanitary service and anti-tuberculosis care for the population.

At all times, it was very difficult to talk about the true prevalence of tuberculosis due to the unequal statistical data coming from different countries. However, at the end of the 20th century, the work carried out by WHO and health authorities of various countries made it possible to form a general idea of the main epidemiological indicators for tuberculosis in different regions of our planet. Since 1997, an annual WHO report on the situation with tuberculosis in the world has been published. In 2003, the report presented information on 210 countries.

At present, it should be recognized that tuberculosis is widespread in all countries of the world. The highest incidence of tuberculosis is detected in Africa, especially in countries with a high prevalence of HIV infection. It accounts for about 1/4 of all newly diagnosed tuberculosis patients. Half of all newly diagnosed patients in the world are in 6 Asian countries: India. China. Bangladesh, Indonesia. Pakistan. Philippines.

It should be said that if in 1970 the incidence rate of tuberculosis in the world was about 70 per 100 thousand, then at the beginning of the 21st century it reached a level of 130 per 100 thousand.

According to WHO, the current rise in the incidence rate is primarily due to the rapid spread of undetected HIV infection on the African continent, which has led to a sharp increase in tuberculosis.

In the 1990s, the highest death rate from tuberculosis in the world was recorded. In 1995, according to WHO, 3 million patients died from tuberculosis every year. In 2003, 1.7 million people died. During the period 2002-2003, the death rate among all patients with tuberculosis decreased by 2.3%, and among HIV-negative patients with tuberculosis - by 3.5%, however, currently about 5,000 patients die every day throughout the world. About 98% of deaths occur among the young, working-age population. In Africa, tuberculosis is the leading cause of death among young women.

In 2003, 8.8 million tuberculosis patients were identified worldwide, of whom 3.9 million were positive for the disease by sputum smear microscopy. There were 15.4 million tuberculosis patients in total, of whom 6.9 million were positive for the disease by sputum smear microscopy. According to WHO, the global incidence rate is currently increasing by 1% annually, mainly due to the increase in incidence in Africa. Among the African population with a high HIV prevalence rate, tuberculosis incidence reaches 400 per 100,000.

The incidence rate varies greatly in different countries and regions. It largely depends on socio-economic development, the level of organization of medical care and, as a consequence, the methods of identifying patients, the quality of examination of the population using these methods, and the completeness of registration. For example, in the USA, patients are identified mainly by tuberculin diagnostics of persons who have been in contact with a patient with tuberculosis. In cases where it is known that a person from contact previously suffered from tuberculosis, radiation diagnostic methods are used, and if sputum is available, it is examined using various methods. In Russia and a number of former Soviet countries, patients with pulmonary tuberculosis are identified based on mass fluorographic examinations of the adult population, tuberculin diagnostics in children and adolescents, and microscopic examination of sputum in coughing patients. In India, African countries and a number of other states where there is no developed system of medical care for the population, tuberculosis is identified mainly by microscopic examination of sputum in coughing patients. Unfortunately, WHO specialists do not provide an analysis of the incidence rate in regions and countries of the world in their annual reports in terms of detection methods and the presence or absence of population screening. Therefore, the information provided in the annual reports cannot be considered completely reliable. Nevertheless, WHO has divided the globe into six regions with different incidence rates (the American continents, Europe, the Eastern Mediterranean, the Western Pacific, Southeast Asia and Africa).

But even in one region in different countries these indicators vary significantly. If the average incidence in North and South America was 27 per 100 thousand population, then its spread on the American continent fluctuated from 5 to 135. For example, in 2002 in the USA and Canada the incidence was 5 per 100 thousand population, in Cuba - 8, in Mexico - 17, in Chile - 35, in Panama - 37, in Argentina - 54, in Haiti - 98, in Peru - 135.

In Central European countries, the incidence rates also varied: in Cyprus, Iceland - 3 per 100 thousand, in Sweden - 4, in Malta - 6, in Italy - 7, in Germany and Israel - 8, in Austria - 11, in Belgium - 12, in England - 14, in Portugal - 44. In Eastern European countries, the incidence of tuberculosis was slightly higher: in Turkey and Poland - 26, in Hungary - 27, in Bosnia and Herzegovina - 41, in Bulgaria - 42, in Estonia - 46, in Armenia - 47, in Belarus -52, in Azerbaijan - 62, in Tajikistan - 65, in Lithuania - 70, in Turkmenistan and Latvia - 77, in Uzbekistan - 80, in Ukraine - 82, in Georgia - 87, in Moldova - 88, in Kyrgyzstan -131, in Romania -133, in Kazakhstan -178. In total, in the countries of Western and Eastern Europe, the average incidence rate was 43 per 100 thousand.

In total, according to WHO data, 373,497 newly diagnosed tuberculosis patients, those with relapsed tuberculosis and other patients were registered in the countries of the European Region in 2002. The WHO European Office identified 18 countries with relatively high incidence rates for the European Region, accounting for 295,240 patients. These are the countries of the former USSR, as well as Romania and Turkey, which the WHO European Office declared to be priorities for anti-tuberculosis work in the plan "Stop Tuberculosis in the European Region" for 2007-2015.

In the Eastern Mediterranean countries, the average incidence rate is 37 per 100,000. It is highest in Djibouti with a population of 693,000 people - 461 per 100,000. The lowest is in the United Arab Emirates - 3 per 100,000. In Jordan it is 6 per 100,000, in Egypt - 16, in Iran - 17, in Pakistan - 35, in Iraq - 49, in Afghanistan - 60, in Sudan - 75.

In the Western Pacific countries, the average incidence rate is 47 per 100,000 population, in Australia - 5 per 100,000, in New Zealand - 9, in China - 36, in Malaysia - 60, in Vietnam - 119, in Mongolia - 150, in the Philippines - 151, in Cambodia - 178.

In the countries of Southeast Asia, the average incidence rate is 94 per 100 thousand. The highest incidence rate of 374 per 100 thousand was registered in the small country of East Timor with a population of 739 thousand people, the lowest - 40 per 100 thousand - in the Maldives. In India, the incidence rate is about 101 per 100 thousand. In Sri Lanka, the incidence rate is 47 per 100 thousand, in Bangladesh - 57, in Indonesia - 71, in Thailand - 80, in Nepal - 123, in the Republic of Korea - 178.

Official incidence rates in 2002 in some countries of the African continent: Namibia - 647 per 100 thousand, Swaziland - 631, South Africa - 481, Zimbabwe - 461, Kenya - 254, Ethiopia - 160, Nigeria - 32.

In 2002, the average incidence rate in Africa, according to WHO, was 148 per 100,000. Over the past decade and a half, the number of newly diagnosed patients in Africa has increased fourfold. The annual death rate from tuberculosis is more than 500,000 people. The developing tuberculosis epidemic on the continent forced the health ministries of African countries to declare a tuberculosis emergency in the region in 2005.

The largest number of tuberculosis patients in absolute figures is identified annually in two countries: India (more than 1 million) and China (more than 1.3 million).

Among the regions of the world, the largest number of patients in 2002 was identified in Southeast Asia (1,487,985 people), Africa (992,054 people) and the Western Pacific (806,112 people). For comparison, a total of 373,497 people were identified in Central and Eastern Europe, 233,648 people in North and South America, and 188,458 people in the Eastern Mediterranean countries.

The highest incidence rate is registered in the following countries: Namibia, Swaziland, South Africa, Zimbabwe, Djibouti, East Timor, Kenya. The lowest (up to 4 per 100 thousand population inclusive) is in Grenada, Barbados, Cyprus, Iceland, Jamaica, Dominica, Puerto Rico, United Arab Emirates. "Zero" incidence rate of tuberculosis is registered in Monaco (population 34 thousand people).

Considering that, according to WHO recommendations, tuberculosis in most countries of the world (with the exception of the USA, Russia and the former USSR countries) is diagnosed mainly by means of simple sputum bacterioscopy, the given incidence rates should be considered underestimated - the true incidence rate in many countries of the world is undoubtedly higher.

Multidrug-resistant tuberculosis has been identified in all 109 countries where WHO or its partners keep records. Every year, about 450,000 new patients are diagnosed worldwide. In recent years, so-called "superdrug resistance" or XDR has begun to be diagnosed. It is characterized by resistance to HR, as well as to fluoroquinolones and one of the second-line drugs for intramuscular administration (kanamycin/amikacin/capreomycin). In the United States, XDR accounts for 4% of all patients with multidrug-resistant tuberculosis. In Latvia - 19%, South Korea - 15%.

At the end of the 20th century, humanity discovered a new dangerous disease - HIV infection. When HIV infection spreads among a population of people infected with tuberculosis mycobacteria, there is a significant risk of the so-called latent tuberculosis infection turning into an active form of tuberculosis. Currently, tuberculosis has become the main cause of death among people with HIV infection.

In 2003, 674 thousand patients with a combination of tuberculosis and HIV infection were identified in the world. In the same year, 229 thousand of such patients died. Currently, the growth of tuberculosis in the world is mainly due to African countries with a high prevalence of HIV infection.

Despite the increase in morbidity worldwide, the prevalence and mortality rates of tuberculosis have decreased somewhat. This is due to the introduction of controlled chemotherapy for patients in a number of countries where previously adequate care was not provided to patients, as well as the receipt of more unified figures from a larger number of countries submitting reports to WHO.

The prevalence of tuberculosis in the world in 1990 was approximately 309 per 100 thousand population, in 2003 - 245 per 100 thousand population. For the period from 2002 to 2003, the rate of decrease in the prevalence of tuberculosis was 5%. About 2 billion people on the globe are infected with Mycobacterium tuberculosis, mainly due to the prevalence of infection in the countries of the so-called "third world". The infected population is a passive reservoir of tuberculosis infection.