Communicable diseases, caused by a specific causative agent, occur as the result of the transmission of the agent or its toxic products from an infected person or other reservoir to a susceptible host, either directly or indirectly, through contaminated food, water, objects in general use, an intermediate host, a vector or inanimate objects/ mater in the environment, or through the exchange of fluid contaminated by the infectious agent .
Every year, around fifteen million people die worldwide from communicable diseases, most commonly from respiratory infections and diarrheal diseases, AIDS, tuberculosis and malaria. In developing countries, communicable diseases make up more than 40% of all causes of death, while in developed countries they make up 1% of causes of death .
In Serbia, infectious diseases make up 0.7% of overall mortality. There were 184 infectious disease-related deaths in Serbia, in 2019, and the greatest number of the deaths can be connected to the flu, AIDS, and tuberculosis .
Infectious diseases remain a significant burden on society, both in Serbia and worldwide. These diseases have been amongst the leading causes of death and invalidity for centuries and have posed a challenge to health safety and human progress. The threat of infectious diseases deepens with the constant appearance of new, unrecognized, and old epidemics of infectious diseases of global significance. During the past three and a half decades, at least thirty new infectious agents which affect humans have emerged, and it has transpired that their origin significantly correlates with socioeconomic and ecological factors. If the situation, caused by these factors, continues to worsen, placing humans in increased contact with disease causing pathogens, there is a concern that communicable diseases may continue to be a formidable challenge. Constant awareness and the implementation of efficient strategies for controlling communicable diseases and the occurrence of disease, remain crucial .
As early as 400 years BC, Hippocrates described a certain number of communicable diseases, and they have remained the focus of scientific development and public health practice to this day. In the 20th century, infectious diseases were considered the key in resolving the health problems of the population, due to the establishing of control of microorganisms and the improvement of results in preventing communicable diseases. We are all witness of the emergence of new communicable diseases which carry new pathogenic threats (SARS, MERS, COVID-19), and which represent a global challenge for public health in the 21st century .
Based on the main entry point of the causative agent, the most important communicable diseases can be categorized into the following groups: respiratory, bowel, parasitic, zoonoses, vector-borne, and sexually transmitted diseases.
Communicable respiratory diseases
Communicable respiratory diseases are predominant in the overall morbidity caused by infectious diseases, and therefore they are of great significance for public health. For most infectious respiratory diseases data are monitored on the basis of passively collected surveillance data, with the exception of seasonal influenza and certain diseases that are preventable with vaccines. The most important infectious respiratory diseases are the following: influenza, acute respiratory infections, tuberculosis, morbilli.
Influenza is a highly infectious viral disease of the respiratory system, which occurs in the population each season, from October until May. According to the estimates of the World Health Organization (WHO), over 100 million people become sick with the flu worldwide, while half a million die as the result of complications related to this disease. Influenza is a great public health and socioeconomic challenge, as it can lead to a decrease in work ability and overburdening of the healthcare system. All countries in the world maintain and improve flu surveillance systems, on the basis of recommendations issued by the World Health Organization and the European Centre for Disease Prevention and Control (ECDC) .
The burden of tuberculosis infection in Serbia has been significantly reduced in the past fifteen years, owing to the consistent implementation of the National Program, which is based on WHO strategies. As a result, there has been a decrease in the tuberculosis case notification rate by 80%, in 2019. Resistant forms of the disease remain a great public health threat .
Communicable bowel diseases
Communicable bowel diseases (bowel infections) are a group of diseases most commonly transmitted through contaminated food, water, objects (indirect transmission), and through direct contact, with dirty hands. They are significant as their incidence can be prevented through the application of very simple measures (hand hygiene, appropriate application of food safety measures). Nevertheless, around a million people all over the world contract these diseases every year. Data for the group of communicable bowel diseases are monitored through passively collected surveillance data. The communicable diseases belonging to this group are the following: salmonelloses, shigelloses, campilobacterioses, yersinioses, lambliases, hepatitis A, botulism .
Communicable parasitic diseases
Communicable parasitic diseases, i.e., parasitoses, are caused or transmitted by parasites. As of 2015, amongst parasitic diseases, mandatory reporting applies only to scabies. Scabies is a frequent cause of epidemics in social welfare institutions, as well as a frequent cause of infection amongst immunodeficient persons. Direct contact is necessary for the transmission of the scabies infectious agent. Poverty, malnutrition, and densely populated collective accommodation contribute to increased incidence of scabies .
Zoonoses are diseases of animals which can also affect people, and which can have one or more entry points. Most diseases in this group have mild clinical presentation and a favorable outcome. However, invasive forms are also registered, which may lead to the lethal outcome, especially in vulnerable population groups, such as newborn babies, aged persons, pregnant women, immunocompromised individuals. Diseases for which there are efficient vaccines (tetanus, rabies) or systematic preventive programs in place, carried out by veterinary services (anthrax, trichinellosis, brucellosis, Q fever, or rabies), have either been eradicated (rabies), or occur sporadically. Data on people contracting zoonoses are collected within passive surveillance of these diseases in the human population .
Communicable vector-borne diseases
Communicable vector-borne diseases are transmitted by vectors, amongst which the most important are the following: lice, mosquitos, fleas, and ticks. The distribution of these diseases depends on both environmental factors and socioeconomic factors. In recent years, globalization and climate change have had a significant impact on the transmission of these diseases. Thus, some diseases, such as dengue, the chikungunya viral infection, West Nile fever, have started to occur in countries where they had previously not been registered. Data for most vector-borne diseases are monitored on the basis of passively collected surveillance data. In addition to vector-borne diseases for which reporting is mandatory, in keeping with the current laws and regulations – malaria, Lyme disease, tick-borne encephalitis, and leishmaniasis, as of 2012, seasonal surveillance has been established for West Nile fever, in the human population .
Sexually transmitted diseases
Sexually transmitted diseases are transmitted via sexual intercourse, and reporting is mandatory for the following: syphilis, gonorrhea, sexually transmitted infections caused by chlamydias, disease caused by the HIV virus .
Other communicable diseases
Other communicable diseases mostly include septicemias caused by different infectious agents. The rise in the incidence of sepsis today represents a global public health problem .
In most countries in the world, reporting infectious diseases is regulated by law. According to the laws and regulations that are currently in force, forty-nine different communicable diseases are reported on in Serbia ,.
The aim of this study is to analyze data on the fluctuation of the overall number of morbidity and mortality, as well as of the morbidity and mortality rates, related to communicable diseases, in the territory of Belgrade, in the period 2015 – 2019.
MATERIALS AND METHODS
This is a descriptive epidemiological study wherein a secondary analysis of data from the Statistical Reviews of Health Activities in Belgrade issued by the City Institute of Public Health of Belgrade, for the period 2015 – 2019, regarding the morbidity and mortality related to infectious diseases, was performed. Data on the number of newly diseased and deceased persons from communicable diseases, as well as the number of newly diseased persons by groups of infectious diseases, in Belgrade, for the observed period (2015 – 2019), were used.
The data flow on communicable diseases in the Statistical Reviews of Health Activities in Belgrade is based on the data from reports (report of disease or death from communicable disease), which health institutions in the territory of Belgrade are obliged to submit to the City Institute of Public Health of Belgrade, according to the Rulebook on Reporting Communicable Diseases in the Republic of Serbia.
The incidence rate was used as an indicator of morbidity. It is calculated in the following way: communicable diseases incidence rate = number of newly diseased persons from communicable diseases in Belgrade in the observed year/population in the territory of Belgrade x 100.000
As an indicator of mortality, the mortality rate was used. It is calculated on the basis of the following formula: communicable diseases mortality rate = number of deceased persons from communicable diseases in Belgrade in the observed year/population in the territory of Belgrade x 100.000
Data on the Belgrade population were taken from the Statistical Yearbook of the Statistical Office of the Republic of Serbia.
In keeping with the defined aim of the study, data are presented in tables and graphs. For assessing morbidity and mortality trends related to communicable diseases, in the observed period, linear trend estimation (curve estimation) was used, whereby the relationship between the two variables was expressed, estimating the value of the dependent variable Y, on the basis of the selected value of the independent variable X.
Linear trend equations were calculated (Y = a + bX), which define the connection between two variables that have a linear relationship, as well as their statistical significance; whereby a is the estimated value of the dependent variable Y where the regression line intersects with the Y axis when X is 0. The regression coefficient (b) is the angle of the line, or the average change of Y for each unit change (increase or decrease) of the independent variable X.
Values of p < 0.05 were considered statistically significant. A positive value of the regression coefficient indicates an upward trend, while a negative value indicates a downward trend.
Data were analyzed with the statistical package SPSS Version 20.0 for Windows (SPSS Inc. Chicago, IL, USA) and with the program Microsoft Office Excel.
In the territory of Belgrade, in the observed period (2015 – 2019), a total of 144,215 persons, newly infected with communicable diseases, was registered. Table 1 presents the number of newly infected persons and the incidence rates of communicable diseases per 100,000 population, in Belgrade, from 2015 and 2019.
In the observed five-year period (2015 – 2019), a downward trend of persons newly infected with communicable diseases is visible. The greatest number of persons newly infected with communicable diseases was in 2016, while the smallest number of newly infected persons was in 2019 (Table 1).
The trend is a decreasing one, for communicable diseases incidence rates in Belgrade, but it is not statistically significant (equation: y = 2158.120 – 134.000 x, p = 0.073) (Graph 1).
In Belgrade, the greatest number of persons newly infected with communicable diseases, in the observed period, related to infectious respiratory diseases. The highest incidence of respiratory disease morbidity was registered in 2018, while the lowest incidence was registered in 2019.
Morbidity related to infectious bowel diseases decreased in the observed period in Belgrade, and the lowest incidence was observed in 2018 and 2019 (Graph 2).
Morbidity related to sexually transmitted diseases, as well as morbidity related to skin, fungal, and parasitic diseases decreased in Belgrade, during the observed period (Graph 2).
The surveillance of certain diseases in the group of communicable respiratory diseases, in Belgrade, in the period 2015 – 2019, shows that the greatest number of newly infected persons contracted the following diseases: chickenpox (varicella), influenza, streptococcal pharyngitis, and tonsillitis.
An epidemic of measles (morbilli) is notable: the greatest number of diseased patients was reported in 2018 (1,893). During 2019, three persons were reported to have contracted measles in Belgrade.
In Belgrade, the number of persons newly infected with tuberculosis declined during the observed period. The highest incidence of persons newly infected with tuberculosis (237) was recorded in 2015, while the lowest incidence (164) was recorded in 2019 (Graph 3).
Amongst sexually transmitted diseases, the number of persons newly infected with the HIV virus had a stable trend during the observed period. The greatest number of persons newly infected with HIV (85) was recorded in 2015, while the smallest number (68) was registered in 2017. A small increase in the number of persons developing AIDS was noted – from 15 cases in 2015, to 19 cases in 2019. Morbidity related to chlamydiosis was almost cut in half in the observed period – from 294 (in 2015) to 151 (in 2019). A slight increase in morbidity related to gonorrhea and syphilis was noted.
In Belgrade, in the observed five-year period (2015 – 2019), an increase of morbidity related to a potentially severe vector-borne disease, West Nile fever (recorded in the group of diseases categorized as ‘Other communicable diseases’), was registered. The greatest number of persons newly infected with West Nile fever (85) was registered in 2018, while the smallest number of them (7) was registered in 2017.
In the observed five-year period (2015 – 2019), 463 persons died from communicable diseases in Belgrade. The number of persons deceased from communicable diseases was noted, with the highest incidence recorded in 2018 and 2019. The greatest number of persons deceased from communicable diseases (107) was recorded in 2018, while the smallest number of persons deceased from communicable diseases (72) was recorded in 2017.
The upward trend in the mortality rate related to communicable diseases in Belgrade was not statistically significant (equation: y = 4.930 + 0.250 x, p=0.369), (Graph 4).
In Belgrade, in the observed period (2015 – 2019), the most common causes of death from communicative diseases were the following: Clostridium difficile, sepsis, AIDS, bacterial meningitis, tuberculosis, and West Nile fever. The percentage of the most frequent causes of death related to communicable diseases in 2019, was as follows: 40% of the deceased died from West Nile fever, 23% died of infection caused by the Clostridium difficile bacterium, 19% of the deceased died from AIDS, 10% died of sepsis, while 8% of the deceased succumbed to tuberculosis.
In the same period, a decrease in the number of persons dying from infection caused by the Clostridium difficile bacterium occurred – from 35 (in 2016) to 21 (in 2019), as well as a decrease in the number of persons deceased from sepsis, by three times – from 27 deceased, in the year 2016, to nine deceased, in 2019.
In the observed period, an increase in the number of persons dying from AIDS was observed – from 10 deceased persons, in 2015, to 17 deceased, in 2019, as was a rise in the number of persons deceased from tuberculosis – from five deceased persons, in 2015, to seven deceased persons, in 2019.
In 2018, 42 persons died from West Nile fever, while in 2019, this number was 36 persons, which makes up around 40% of all causes of death from communicable diseases (Graph 5).
In the territory of Belgrade, in the observed period (2015 – 2019), a decrease in the trend of infectious diseases incidence was observed, however, without statistical significance. The greatest number of newly infected persons was from the group of infectious respiratory diseases. In the group of communicable respiratory diseases, the leading cause of morbidity was related to chickenpox (varicella). The greatest number of newly diseased persons suffering from respiratory infections was registered in 2018, when the highest number of measles cases was also reported. In the group of sexually transmitted diseases, morbidity related to chlamydiosis decreased by 50%. In Belgrade, the number of persons newly infected with the West Nile fever increased manifold in 2018, which was the result of an epidemic of this disease in Serbia, in 2018 and 2019. In Belgrade, an increasing trend in mortality related to communicable diseases was observed, however, without statistical significance. Mortality related to West Nile fever increased manifold in Belgrade, during 2018 and 2019, which affected the upward trend of mortality related to communicable diseases. An increase in the number of persons dying from AIDS and tuberculosis was also noted in 2018 and 2019.
In a study of global societal burden of disease (369 diseases), carried out in 204 countries, in 2019, published by the GBD 2019 Diseases and Injuries Collaborators, six communicable diseases were amongst the ten leading causes of years of life lost due to disability in children under the age of ten years, this being due to the following: lower respiratory infections (ranked second), diarrheal diseases (ranked third), malaria (ranked fifth), meningitis (ranked sixth), whooping cough (ranked ninth), and congenital syphilis (ranked tenth) .
According to the data of the Institute of Public Health of Serbia Dr Milan Jovanović Batut, the number of reported cases of morbidity related to communicable diseases in Serbia was significantly higher in 2020, as compared to 2019. The increase in the number of cases in 2020 was the consequence of the outbreak of a new disease – COVID-19, which accounted for 79% in the morbidity structure .
According to the data published on the site of the City Institute of Public Health of Belgrade, regarding the fluctuation of infectious diseases in Belgrade, for March 2022, it is evident that the incidence of communicable diseases was 367.13 (per 100,000), which is four times less than the observed period in our study. Amongst the newly infected persons in March 2022, most patients were reported to be cases of COVID-19 (4,344), chickenpox (1,150), and influenza (380), which shows that communicable respiratory diseases are the most frequent in the overall morbidity related to infectious diseases .
In the period from October 2021 to the end of July 2022, the Belgrade Institute for Student Health Care conducted a survey amongst 11,147 University of Belgrade students, who were tested for SARS-CoV-2. The survey showed that 3,278 (29.4%) students tested positive for the new virus .
Due to the unavailability of data, the limitations of this study are reflected in the fact that the study has not presented the trend of mortality and morbidity related to communicable diseases in the Belgrade population, by gender and by age, as well as in the fact that we were unable to present the trends of standardized rates of incidence and mortality.
In Belgrade, in the observed period (2015 – 2019), morbidity related to communicable diseases decreased, while mortality increased. The incidence rate of communicable diseases was declining, while the trend of the mortality rate was on the rise, however, without statistical significance. The greatest number of newly infected persons suffering from communicable diseases was related to respiratory infections, amongst whom the majority contracted chickenpox, influenza, streptococcal pharyngitis and tonsilitis. An epidemic of measles was registered during 2017 and 2018, when the greatest number of cases was reported – 1,893 (in 2018). An epidemic of West Nile fever was registered in 2018 and 2019, when the highest incidence of this disease was registered – 85 newly infected persons (in 2018). The most frequent causes of death from communicable diseases were as follows: Clostridium difficile, sepsis, AIDS, bacterial meningitis, tuberculosis, and West Nile fever. During 2018 and 2019, around 40% of all causes of death related to West Nile fever.
Although they are highly preventable, communicable diseases remain a constant threat and a leading cause of mortality. In addition to general and personal hygiene measures, wearing protective masks, avoiding risky behavior and using protection against sexually transmitted diseases, it is also necessary to focus public health measures on environmental protection and the prevention of the spread of infectious agents outside their habitats, as well as on the prevention of the emergence of new infectious agents.