In December 2019, an outbreak of a new respiratory infection was registered in the Chinese city of Wuhan. This infection was accompanied with an increase in the number of patients with pneumonia of unknown etiology. In a relatively short time, the outbreak became a pandemic. The patients exhibited symptoms of an upper respiratory tract infection: sore throat and rhinorrhea, as well as fever, cough, myalgia, shortness of breath, and signs of pneumonia visible on the chest x-ray pictures. Subsequently, it was established that the causative agent of this infection is a new coronavirus, dubbed SARS-CoV-2. The disease that followed was named COVID-19 [1].

As part of a large-scale study conducted in China, the researchers analyzed data describing the course of the disease in 1099 patients with laboratory-confirmed COVID-19 diagnosis. It was established that the majority of hospitalized patients (91.1%) were diagnosed with pneumonia [2].

In Russia, the first cases of COVID-19 were diagnosed in February 2020. The infected were citizens of the PRC. By early July, the number cases registered and reported has grown to over 650,000 [3–5].

Every year, there are 1.5 million community-acquired pneumonia (CAP) cases registered in Russia, which translates into approximately 390 cases per 100,000 people.

The average mortality rate is up to 5% of the number of cases [6].

According to epidemiological studies carried out in a number of foreign countries, the incidence rate of CAP varies depending on age, reaching the minimum in young and middleaged populations (1–11.6 cases per 1000 people). In children under 17, the incidence of CAP ranges from 2 to 15 cases per 1000 people in different years. The group most susceptible to CAP is comprised of the elderly people, over 70 years of age:

annually 25–44 cases per 1000 people [7, 8].

The situation with CAP incidence in USA is also alarming. There are 5–6 million CAP cases registered there annually, with 1.5 million of them requiring inpatient treatment [9, 10].

In recent years, the number of deaths from pneumonia has increased. According to the American Thoracic Society, for 18–20% of the total number of CAP patients the disease ends in death [11].

The outcome of CAP depends on a number of various risk factors, which, when exposed to, increase the likelihood of death. Of great importance are the patient's age, clinical form and severity of the disease, comorbidities [12].

According to the research data, young and middle-aged patients with mild and moderate clinical forms of CAP and without concomitant pathologies recover well; for these age groups, the mortality rate is 1–3% [13].

In elderly patients that endure CAP in its severe form and have upper respiratory tract comorbidities, cancers, cardiological diseases, alcoholism in the background, the mortality rate rises up to 15–58% [14].

At the same time, it has been shown that CAP becomes more common when influenza and acute respiratory viral infections (ARVI) are on the rise, and the highest mortality from CAP is recorded 1–2 months after the peaks of influenza and ARVI epidemics [15].

Since COVID-19 is also an acute respiratory infection, it will be relevant to study epidemic features of CAP during the COVID-19 epidemic.

This study aimed to investigate manifestations of community-acquired pneumonia (CAP) epidemic process during the COVID-19 epidemic in the Russian Federation.

METHODS

The long-term dynamics of CAP incidence in the Russian

Federation was analyzed in the context of a descriptive retrospective epidemiological study relying on the data collected with the Federal Statistical Observation Form #2 "Information on Infectious and Parasitic Diseases" (hereinafter — Form #2) in 2013–2018.

Inside a year, the CAP incidence dynamics analysis and the calculation of the seasonal incidence level in Russia relied on the data collected with Form #1 in 2013–2019.

The 2019 incidence rate analysis made use of the data collected with the Federal Statistical Observation Form #1 "Information on Infectious and Parasitic Diseases (monthly)" that covered January–December 2019 (hereinafter — Form #1). We established the yearly CAP incidence level and calculated the prognostic incidence rate for the coming period.

To analyze the incidence of COVID-19, we relied on the official information on the number of cases registered in the Russian Federation [16]. Form #1 data for January–July 2020 allowed assessing the incidence of CAP against the background of the COVID-19 epidemic.

To assess the differences in relative indicators, we calculated the 95% CI (m ± 2.45 × SEM, where m is the mean incidence over the period, SEM is the standard error of the mean). The differences were considered statistically significant at p < 0.05. The least square method enabled calculation of the long-term CAP incidence dynamics, which was assessed by the average annual increase/decrease rate. We compared the value obtained with the gradation suggested by V.D. Belyakov [17]. To assess the relationship between the incidence of CAP and COVID-19, we established the Pearson correlation coefficient (r_xy). The relationship was considered statistically significant at p < 0.05, with Chaddock's scale used to identify the strength of the relationship.

Microsoft Excel 2013 (Microsoft; USA) application was used to process and analyze the data obtained.

RESULTS

The analysis of structure of infectious and parasitic disease cases registered in 2013–2019 revealed that in Russia, acute infections of the upper respiratory tract of multiple and unspecified localization (ICD-10 code: J06) (ARI) are the most common diseases, with their share averaging at 90.7% within the period. The share of CAP is 1.7%, and influenza accounts for 0.6% of cases (fig. 1).

The upward trend with the annual growth rate (AGR) of 6.4% was characteristic for CAP incidence in Russia in 2013–2019. Every year, there are 492–760 thousand new cases of the disease registered among the overall country's population, including 165–291 thousand cases in children under 17.

Children under 14 and up to 17, inclusively, have also exhibited a pronounced CAP incidence upward trend, with the AGR of 6.8% and 5.9%, respectively.

The 7-year analysis of CAP incidence in the Russian Federation showed that, on average, 608345 cases of CAP are registered annually among the adult population (the incidence rate is 416.4 per 100 thousand population), of which 216146 cases are in children under 17 years of age inclusively (753.4 per 100 thousand), including 201,078 cases (817.7 per 100 thousand of the population) in children under 14 years of age (tab. 1).

In general, the CAP incidence in 2019 was 5.3% greater than in 2018. For children, the trend is the same, with the growth at 7.6%.

In the Russian Federation, within the period analyzed 64.7% (95% CI [63.1; 66.3]) of the CAP cases were registered among adults, 2.4% — among children aged 15–17 (95% CI [1.9; 2.9]) and 32.9% — in children under 14 inclusively (95% CI [31.8; 34.1]).

Analysis of the long-term dynamics of CAP incidence reveals a steady growth of the level thereof (approximation confidence factor R² = 0.72), with additional 26.5 cases per 100 thousand people registered every year. These indicators considered, the estimated 2020 CAP incidence rate in the overall population is 522.6 cases per 100 thousand people (95% CI [388.2; 657.1])

(fig. 2).

Analyzing the yearly CAP incidence data of 2013–2019, we established seasonal character of the disease: about 70% of all the cases registered annually belong to autumn and winter periods.

The level of year-round and seasonal incidence of CAP in the overall population of the Russian Federation within the investigated period is 39.2 and 43.8 cases per 100 thousand people, respectively (fig. 3). The obtained indicators allow determining when the incidence starts and ends rising, as well as to establish favorable and unfavorable periods.

Thus, in 2019, within the periods from January to April and from October to December population of the Russian Federation contracted CAP at a greater scale than on average throughout the year. As for the seasonal incidence levels, they are exceeded in January–March and October–December periods.

The analysis of seasonal manifestations revealed a more pronounced epidemiological stress peculiar to the first half of 2019 compared to the second part of the year.

In 2019, CAP incidence peaked in February, when it amounted to 62.4 per 100 thousand people, exceeding the year-round and seasonal levels by 71% and 42.5%, respectively.

Based on the actual CAP incidence recorded in 2013– 2019, we calculated the prognostic level of monthly incidence for 2020. The lowest 2020 CAP incidence level in Russia (overall population) is forecast for July and August, with the figures being 20.7 and 21 cases per 100 thousand people, respectively. The peak is expected in in January, February and November of the year, with 46.2 and 40.0 cases per 100 thousand people, respectively.

The 2020 incidence forecast should approach the average rate recorded in the 2013–2019 period; the expected match value is 89.9% (± 9.6%; p < 0.05).

At the same time, against the background of SARS-CoV-2, 2020 saw a statistically significant (p < 0.05) discrepancy between the actual CAP incidence and the predicted level: in February, the gap reached 27.9%, and in July it has grown to 558.5% (fig. 4).

With the epidemic spread of the new coronavirus infection (COVID-19) in Russia, from the scientific and practical viewpoints it is particularly interesting to study the results of the analysis comparing January–July 2020 CAP incidence data to the figures recorded during January–July 2019, when the COVID-19 epidemic was on the rise.

Within the period from January to July 2020, the incidence of CAP in the population of the Russian Federation increased by 125.2% compared to the same period of 2019, and reached 673.9 cases per 100 thousand people (tab. 2).

Considered on the level of Federal Districts (FD), the greatest CAP incidence growth during the period analyzed (January-July), compared to the same period of the previous year, was registered in the Central FD (+282.4%) and the North Caucasian FD (+254%). In absolute terms, it is 278089 and 41203 cases, respectively.

At the same time, in the Far Eastern FD the CAP incidence dropped insignificantly by –4.1%.

From March to May 2020, the incidence of COVID-19 on the territory of the Russian Federation was growing steadily. In January and February, there were no COVID-19 cases registered. The most significant increase was recorded in May 2020, when the incidence grew 2.7 times compared to April 2020 (from 75.7 cases to 203.6 cases per 100 thousand people, respectively).

It should be noted that the analysis of relationship between CAP and COVID-19 incidence in the population of the Russian Federation within the period from January to July 2020 allowed us to establish a direct, very high and statistically significant link between these indicators (Pearson's coefficient r_xy = 0.932; t = 5.731; p < 0,01).

DISCUSSION

The results of the study allowed investigating manifestations of the CAP epidemic process before and during the COVID-19 epidemic. Given that COVID-19 is a new infectious disease, most studies cover clinical manifestations of this infection [18, 19].

CONCLUSIONS

1. The long-term dynamics of CAP incidence in Russia shows a pronounced upward trend, which is seen in both the overall population (AGR = 6.4%) and among children (AGR = 6.8%). 2. Within the period analyzed, the majority of cases were adults (on average, 64.7% of the registered CAP cases). 3. In the period from 2013 to 2019, the year-round CAP incidence rate in the overall population of Russia is 39.2 cases per 100 thousand people, and the seasonal level is 43.8 cases per 100 thousand people. 4. In 2020, against the background of SARS-CoV-2 circulation, the discrepancy between the actual incidence of CAP and the predicted incidence value reached over 558% (July 2020), which indicates an increase in the incidence of CAP during the COVID-19 epidemic. 5. A direct, statistically significant correlation between the incidence of CAP and COVID-19 reveals the relationship between the development of the epidemic process of these infections.