Epidemiological assessment of acute viral respiratory infections with the improvement of surveillance and response measures: 331.01 – Epidemiology: Summary of the PhD thesis in medical sciences

Abstract

Relevance of the Topic. Influenza, acute respiratory infections (ARI), and severe acute respiratory infections (SARI) are globally widespread infectious diseases, accounting for up to 95% of infectious diseases in some regions. These infections, characterized by high levels of morbidity and mortality, have a significant impact on public health, and considerable pressure on the healthcare system, resulting in substantial economic losses. [1,2]. Globally, influenza epidemics affect approximately one billion people annually, with three to five million developing severe forms of the disease, and between 290,000 and 650,000 losing their lives [3]. Up to 20% of the general population is infected with influenza annually [4]. A study highlighted that influenza-associated respiratory infections in children under five years old account for 7% of total cases, 5% of hospitalizations, and 4% of deaths globally, with the majority occurring in low- and middle-income countries [5]. Lafond K. et al. demonstrates that influenza viruses are responsible for over five million hospitalizations worldwide annually, including more than two million in Europe [6]. People with lower socioeconomic status are disproportionately affected by influenza due to limited access to healthcare. In low- and middle-income countries, hospitalizations in intensive care units due to influenza are approximately seven times more frequent compared to high-income countries, with case severity increasing with age and the presence of comorbidities [7]. Influenza has severe complications, which increase hospitalization and mortality rates [8]. Influenza viruses frequently undergo mutations and recombinations, influencing the evolution of epidemics and the distribution of cases. Genetic monitoring of influenza viruses is essential for detecting mutations and ensuring effective infection and epidemic management [9,10,11]. Seasonal influenza epidemics typically occur during the winter months [12,13]. Antiviral resistance complicates the treatment and control of epidemics, and continuous surveillance of resistance is crucial for adjusting therapeutic strategies [14]. In 2019, the World Health Organization (WHO) identified influenza as a major global threat and established partnerships to ensure equitable access to diagnostics, vaccines, and antivirals, particularly for developing countries [15]. The WHO is implementing the Global Influenza Strategy (2019-2030) to optimize surveillance and promote research and innovation in this field. The study conducted by Kiseleva I. et al. in 2022 reveals that ARIs are among the most common infections globally. Although they are generally mild and self-limiting, their behavior can vary under pandemic conditions, such as the replacement of influenza viruses by Rhinoviruses and Respiratory Syncytial Virus in some regions [16]. The prevalence of ARIs is influenced by pathogen variability and rapid transmission, especially airborne. Immunity is often incomplete or short-lived, leading to frequent reinfections and temporary immunosuppressive effects [17,18]. The WHO has established criteria for SARI to facilitate the monitoring of influenza-associated hospitalizations, and the definition has been widely adopted for assessing its public health impact [19]. The results of a 2023 study in Tunisia indicate an increase in post-pandemic SARI cases, with influenza A and B strains as the primary causes, highlighting the need for proactive strategies [20]. Another observational study, conducted in 23 countries, reports an overall mortality rate of 9.5%, with the highest rate among individuals over 60 years of age (18.6%) and children under five years old (1%) [21]. Recent studies highlight the significant economic impact of influenza. A 2019 study from Turkey reported an average hospitalization cost of $3,274 for influenza patients, compared to $2,880 for those not confirmed. Influenza vaccination reduced these costs by 4.8 times, with hospitalization costs for vaccinated individuals amounting to $780, compared to $3,762 for those unvaccinated. Community costs exceed $22 million for individuals aged 18-65 and $15 million for those over 65, emphasizing the need for targeted surveillance and prevention [22]. Acute upper respiratory infections generate global costs of approximately 25 billion dollars [1,2]. A study in 20 countries reported average hospitalization costs of €17,804 for adults over 50 and €129 for outpatient care. Costs increase significantly for elderly patients and those with comorbidities [23]. Another 2022 study showed that patients with SARI confirmed with influenza virus had direct medical costs of $700, and total costs amounted to $848 per patient, being three times higher in the elderly [24]. These results underline the economic burden of respiratory infections and the need for effective prevention and control measures to reduce the global economic impact. Seasonal influenza vaccination is the most effective method for preventing influenza [25,26]. Although these programs have been implemented for decades in high-income countries [27], vaccine uptake remains low in low- and middle-income countries, where mortality and hospitalization rates are higher [28,29,6,30]. In 2022, out of the 194 WHO member states, 128 (66%) had seasonal flu vaccination policies [31]. Low vaccination rates in low- and middle-income countries are influenced by factors such as lack of government involvement and competition for limited health resources. In contrast, high-income countries have higher vaccination rates, associated with a higher socioeconomic status [32]. According to estimates, approximately one in five unvaccinated children and one in ten unvaccinated adult contract seasonal influenza annually [33]. Seasonal influenza vaccination has demonstrated a significant impact in reducing the incidence of influenza, particularly among vulnerable groups, by decreasing severe cases and deaths. Continuous evaluation of program effectiveness is crucial for improving vaccination strategies [34]. Surveillance of viral respiratory infections remains a global challenge due to the unequal capacities of national influenza centers, limited resources, and inefficient monitoring mechanisms [35]. The WHO recommends monitoring influenza, ARIs, and SARI to reduce morbidity and mortality, focusing on geographical spread, epidemic intensity, viral strain prevalence, and antiviral resistance. These require dedicated research projects to improve prevention, surveillance, and response strategies. Aim of the research: Assessment of the epidemiological and virological characteristics that are associated with the morbidity and mortality caused by influenza, acute respiratory infections (ARI), and severe acute respiratory infections (SARI), depending on the circulating strains of the influenza virus, to improve prevention, surveillance, and response measures at national level [...].