COVID-19 Epidemiology in Türkiye

Abstract

The World Health Organization declared the current pandemic, known as severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection, which began in China in December 2019. SARS-CoV-2 has the third highest recorded pathogenicity, with mortality rates varying from 6 to 10.5% based on comorbidity of the individual infected with the virus. Epidemiologic studies have critical importance in the fight against any disease. This chapter discusses demographic and epidemiologic literature data including age, gender, reinfection, death, and vaccination rates reported in numerous articles during the pandemic process from Türkiye.

1. Introduction

Epidemiology is critical in the fight against any disease. Epidemiology, which is the study of how diseases spread, and why, has played a significant role in the effort to understand, contain, and respond to COVID-19. The pandemic has altered epidemiology and expanded its scope. It is a cornerstone of public health, determining health policy and evidence-based practice by identifying disease risk factors and preventive healthcare targets.

The World Health Organization (WHO) declared a coronavirus pandemic in March 2020, following the outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in Wuhan, China, in December 2019. SARS-CoV-2 is one of the members of coronavirus pathogens, e.g., SARS-CoV-1, MERS-Co-V (Middle East respiratory syndrome) with mortality rates ranging from 6 to 10.5% depending on the infected individuals [1, 2]. As long as SARS-CoV-2 continues to spread rapidly around the world, a better understanding of the underlying level of transmission and infection severity is critical for guiding the pandemic response [3].

The value of quick diagnoses has been proven by the COVID-19 pandemic.

2. Characteristics of the SARS-CoV-2 and interaction with the host

SARS-CoV-2 is the one of the single-stranded RNA viruses in Coronavirus family, which includes nearly 40 species [2].

As a result of sequencing analysis, between SARS-CoV-2 and SARS-Co-VS proteins similarity was detected up to 80%. Based on this analysis, SARS-CoV-2 is classified in the β-coronavirus cluster [2]. The SARS-CoV-2S protein has a 15-fold higher affinity for the human angiotensin-converting enzyme 2 (ACE2) receptor [4]. ACE 2 receptor as well as transmembrane protease serine 2 (TMPRSS 2) enzyme plays a role in the induction of S protein. The S protein’s scission regulates the entire mechanism.

3. Transmission

The primary mode of SARS-CoV-2 transmission is person-to-person respiratory transmission [5]. It is considered to spread mainly through intimate interaction via respiratory particles; a virus released in respiratory secretions in an infected person coughs, sneezes, or speaks can infect another person if inhaled or comes into direct contact with mucous membranes. Transmission can also occur via touching contaminated surfaces.

SARS-CoV-2 has been detected in non-respiratory specimens including stool, blood, ocular secretions, but their role in transmission is unknown.

4. Incubation period

The incubation period of an infectious disease is the time between exposure to an infectious agent and the appearance of signs and symptoms of the disease. A disease’s incubation period can vary greatly from person to person. Understanding the incubation period data for a novel infectious agent is useful for estimating the transmission potential and pandemic, locating active cases, assessing the effectiveness of entry screening and contact tracing, and determining the pathogen’s relative infectiousness. It is assumed to have a 14-day incubation period after being exposed to the pathogen [6].

5. Cytokine storm of SARS-CoV-2 infection

The severity of SARS-CoV-2 disease is linked to cytokine storming, which occurs when IL-2R, IL-6, IL-10, and TNF-a levels rise [7]. It is linked to the development of severe alveolar damage and lung inflammation as a distinct pathological picture of acute respiratory distress syndrome [7].

6. Incidence of SARS-CoV-2 infection in Türkiye

On March 10, 2020, the first COVID-19 case was diagnosed in Türkiye. Since the outbreak’s inception, the city with the highest population density in the country, Istanbul, has reported the greatest number of cases [8]. According to last data, in Türkiye, coronavirus cases 17.042.722 and 101.492 coronavirus deaths were reported (https://www.worldometers.info/coronavirus/country/turkey/).

7. Clinical findings and symptoms

SARS-CoV-2 infection causes acute and highly fatal pneumonia with fever (83–99%), dry cough (60–82%), dyspnea, and bilateral ground-glass opacity on radiological thorax imaging [9]. The severity of the disease was determined primarily by clinical features and laboratory testing and was categorized as asymptomatic infection, mild, moderate, severe, and critical disease [10].

8. Distribution by age and gender in SARS-CoV-2 infection

COVID-19 can be seen in all age groups. In elderly persons and patients suffering from chronic diseases, COVID-19 may be more severe and mortal. The number of reported cases in pediatric population and the rate of serious illness are low. COVID-19 is commonly asymptomatic in children, and it is an important matter of attention during the pandemic. This situation contributes to the spread of infection.

The infection fatality ratio is estimated to be lowest among 5- to 9-year-old children, with an increased rate by age among individuals older than 30 years [3].

In Türkiye, children account for around 1–5% of COVID-19 cases [11]. Considering SARS-CoV-2 patients, it is noteworthy that the number of pediatric patients is considerably less than adults. The first reason that comes to mind to explain this situation is ACE activity [6]. It appears that COVID-19 causes less severe disease in children than in adults. The asymptomatic, mild, or moderate disease affects an estimated 90% of pediatric patients. Even so, 6.7% of the cases were severe. Severe disease has been reported in patients younger than one year of age, including children with an underlying disease [11, 12]. Various studies on the disease management strategies in pediatric patients are being conducted. One research examined 220 pediatric COVID-19 patients, 48.2% of whom were male, with a median age of 10 years, and 9.5% of whom had underlying diseases. The authors concluded that the course of COVID-19 seemed to be mild and management strategy primarily should consist of supportive care [13].

The death rate in men is higher than in women. As an explanation for this situation, the contribution of smoking rate, consumption of alcohol rate, and other risk factors to disease severity were considered in the etiology.

9. Protection

Based on previous experience with other respiratory virus, it is critical to use personal protective equipment (PPE) on a consistent basis to reduce nosocomial transmission [14].

10. COVID-19 prevalence in healthcare workers

According to the data of the Ministry of Health, research assistant doctors (12.3%) and nurses (11.1%) had the highest seropositivity rates, respectively. It has been suggested that the reason for this may be that health workers who actively participate in patient sampling, diagnosis, and treatment have greater rates of SARS-CoV-2 exposure [15].

11. MIS-C syndrome

Multisystem inflammatory syndrome in children (MIS-C) is a rare post-infectious hyperinflammatory disorder associated with SARS-CoV-2 [16]. MIS-C syndrome should be considered as a differential diagnosis in cases where persistent fever, fatigue, hypotension, cardiac dysfunction, and gastrointestinal symptoms are prominent [17]. Referring to research done on 101 patients in Türkiye, the median time of hospitalization was reported as 10 days. In the same study, the rate of need for intensive care was reported as 37.6% and the rate of need for mechanical ventilation was reported as 10.8% [17]. Procalcitonin, C-reactive protein, international normalized ratio, D-dimer, and creatinine levels were also found to be higher in children who needed intensive care unit stay [17]. Nearly half of the patients received anticoagulants and aspirin to prevent the potential risk of thrombosis caused on by SARS-CoV-2 infection. Intravenous immunoglobulin was applied to treat the majority of patients; the dosage was 2 g/kg in 82% of cases and 4 g/kg in 10%. Echocardiography was performed in 85 patients and abnormal findings were noted in 45 (52.9%) patients [17].

12. Anosmia

Anosmia and ageusia are particular symptoms reported in COVID-19 patients. According to the data obtained by examining a large case series across Türkiye, anosmia (43.3%) and ageusia (44.5%) were frequently observed after general symptoms [18]. There is no definitive treatment regimen specified in the guidelines against anosmia associated with COVID-19. It was observed that anosmia resolved at a rate of 91.6% [18].

13. Vitamin D status

As a result of the study conducted with 155 participants (COVID-19 patients n:75, control group n:80) in Türkiye, mean vitamin D level was greater in the control group than the COVID-19 patient group [19]. There are other study results confirming this situation [20]. Patients with low vitamin D levels experienced greater instances of respiratory distress, weakness, anosmia, headache, myalgia, and ageusia but significantly lower instances of fever and cough [19]. Comparing the low vitamin D group to the normal vitamin D group, the mean lymphocyte count was considerably lower in the low vitamin D group [19]. The number of days of hospitalization was negatively correlated with vitamin D levels [19].

14. Mental health

In order to establish COVID-19 precautions in Türkiye, a scientific committee was set up. The day following the first case was announced, on March 12, all schools and institutions were closed. Online education for students was quickly put in place. Anxiety brought on by COVID-19 has affected everyone’s mental health. During the lockdown, people began to experience tension in their relationships with others as a result of increasing anxiety. As people attempt to adjust to the new circumstances, a variety of different behaviors have been reported. These behaviors include communication issues between spouses, conflict between parents and children, an increase in irritability and outbursts, depressive and anxious moods, excessive use of social media, and binge eating. Additionally, eating and sleeping habits significantly disturbed [21].

15. COVID-19 incidence in chronic disease patients in Türkiye

At least one-quarter of patients with COVID-19 have one of the chronic diseases as a comorbidity such as diabetes mellitus, hypertension, and asthma [22]. In a Turkish study, the most common comorbidities were hypertension (9.1%), diabetes (7.6%), and coronary artery disease (6.9%) [23].

16. Mortality in Türkiye

In Türkiye, which has a powerful health system, the majority of hospitals have been converted into pandemic hospitals, scheduled procedures have been postponed, and medical professionals have been reassigned to treat COVID-19. According to study, the overall mortality rate was 1.4% [23]. Re-infection caused death in 2% of the cases [23].

17. What is a reinfection and how are the rates in Türkiye?

A reinfection occurs when an individual becomes infected with COVID-19, recovers, passes a certain amount of time, and later becomes infected again. If a person tests positive again in ≥90 days after their first-positive SARS-CoV-2 RT-PCR test, they are considered to have been reinfected. The study included 58,811 patients diagnosed with COVID-19 between March 2020 and August 2021. Re-infection rate was reported in 421 patients (0, 7%) [23]. The cases had an average age of 38.0 ± 16.0 years, with 51% of them being female. About 17.6% of all re-infected cases were healthcare workers. The prevalence of chronic diseases was reported to be 31.1% [23]. While the hospitalization rate for the first infection was 15.9%, it was 9.1% for re-infection. The re-infection admission rate to the intensive care unit was higher (2.9%), than the first infection (0.5%) [23].

18. Vaccination in Türkiye

The SARS-CoV-2 pandemic, which started in 2019, has been a very difficult global pandemic process. Vaccination is among the most effective public health interventions that modern medicine has to offer [24]. Vaccination is regarded as the most important tool in controlling the pandemic [25].

In addition to vaccination, vitamin D supplementation plays an important role in immune system modulation by suppressing proinflammatory cytokines [26, 27]. There were no hospitalizations or deaths among fully vaccinated patients. Furthermore, none of the fatal cases had completed their vaccination schedule [23].

Unvaccinated individuals make about 2/3 of re-infection cases. About 5.6% of cases were fully vaccinated. In fully vaccinated patients, no hospitalization or mortality was observed. Some of them, which were fully vaccinated, were performed a chest CT and had no radiological sign was found in any of them [23].