Introduction
Coronavirus is a type of virus belonging to the Coronaviridae family, which is phylogenetically classified into four groups: Alpha, Beta, Gamma, and Delta. The reservoirs of coronaviruses have been identified in mammals and birds, including bats, rodents, pigs, dogs, cattle, poultry, horses, and humans [۱]. A novel coronavirus, termed “SARS-CoV-2,” was first identified in Wuhan, China, on December 31, 2019, and was later designated as “COVID-19.” Human coronaviruses (HCoVs) are associated with a range of respiratory diseases of varying severity, including the common cold, pneumonia, and bronchitis [۲]. Individuals of all ages are susceptible to COVID-19; however, the risk of severe infections, complications, disabilities, and mortality is significantly higher in the elderly population [۳، ۴]. Physiological changes associated with aging, along with chronic diseases, such as cardiovascular and pulmonary conditions, diabetes, dementia, and polypharmacy, contribute to poor disease outcomes in older adults [۵].
Respiratory diseases typically exhibit a U-shaped mortality curve, with higher mortality rates observed among children and the elderly. However, in the case of COVID-19, this pattern differs, with mortality rates increasing significantly in older adults while children exhibit lower susceptibility to fatal outcomes [۶]. Various comorbidities, such as renal failure, diabetes, hypertension, arthritis, cardiovascular diseases, and chronic obstructive pulmonary disease are more prevalent in the elderly. The present study examines the epidemiological profile of COVID-19 in the elderly population of Guilan Province, Iran. The findings of this study provide valuable insights into infectious disease prevention and the development of targeted intervention programs for elderly populations, particularly during epidemic and pandemic periods.

Methods
This cross-sectional, multicenter study was designed based on the medical care monitoring center surveillance and registry system to assess the epidemiological profile of COVID-19 in Guilan  Province, Northern Iran, from March 2019 to March 2021. The study employed a census sampling approach, including all hospitalized elderly patients diagnosed with COVID-19 within the given time frame.
A checklist comprising different variables, such as age, sex, city of admission, disease onset date, clinical manifestations, underlying conditions, final health status, and vaccination history was completed by researchers in collaboration with healthcare professionals from the Deputy of Treatment at Guilan University of Medical Sciences. The data were entered into SPSS software, version 24 for statistical analysis.

Results
A total of 42481 elderly patients aged 60 years and above were hospitalized due to COVID-19 in Guilan  Province, Iran, over the 24-month study period. Among them, 22026(52%) were male, and 20455(48%) were female. Regarding age distribution, 18342(43%) patients belonged to the 60–69 age group (8864 females and 9478 males), 13 531(32%) were in the 70–79 age group (6 675 females and 6 856 males), 9 143(22%) were in the 80–89 age group (4273 females and 4870 males), and 1465 (3.5%) were aged 90 years and above (643 females and 822 males).
A chi-square statistical analysis revealed a significant association between age and sex among hospitalized patients (P<0.001). However, no significant association was found between mortality and sex (P>0.5). In contrast, a significant association was observed between mortality and age, with the probability of death increasing with advancing age (P<0.001).
Among all hospitalized elderly patients, 8176(19%) had received at least one dose of a COVID-19 vaccine at the time of admission. The highest vaccination rate was observed in patients aged 90 years and above (317 cases, 21%), while the lowest rate was recorded in the 60–69-year age group (3,329 cases, 18%). The most prevalent comorbidities among elderly COVID-19 patients were cardiovascular diseases and hypertension (10739 cases, 25.3%), followed by diabetes (10302 cases, 24.3%).
A chi-square analysis examining the relationship between clinical symptoms and mortality demonstrated a significant association between mortality and symptoms such as fever, myalgia, cough, respiratory distress, and decreased consciousness (P<0.001).

Conclusion
Overall, 13.9% of the elderly population aged 60 years and above in Guilan  Province were hospitalized due to COVID-19, with a higher hospitalization rate observed in males (9.78%) compared to females (8.52%). Guilan  Province (Iran) has a total elderly population of 465487 individuals, distributed as follows: 271578 in the 60–69-year age group, with 18 342 hospitalizations (6.75%); 131 411 in the 70–79-year age group, with 13531 hospitalizations (10.30%); 52801 in the 80–89-year age group, with 9143 hospitalizations (17.32%); and 9807 in the above 90-year age group, with 1465 hospitalizations (14.94%). The frequency of hospitalization increased with advancing age.
Among all hospitalized elderly patients, the highest vaccination rate (21%) was observed in individuals aged 90 years and above, while the lowest rate (18%) was recorded in the 60–69-year age group. This discrepancy may be attributed to national vaccination strategies prioritizing older age groups. Of the 42481 hospitalized elderly COVID-19 patients, 6289(14.8%) died. Among them, 3084(49%) had a positive polymerase chain reaction test result. Mortality rates among different age groups were as follows: 1099(51.6%) in the 60–69-year age group, 1044(50.8%) in the 70–79-year age group, 796(45.1%) in the 80–89 age group, and 145(42.1%) in the age group above 90 years.
This study highlights the increased vulnerability of the elderly to COVID-19, with advancing age correlating with higher infection and mortality rates. Male elderly individuals were at greater risk of infection compared to females. Additionally, the presence of comorbidities such as diabetes and cardiovascular diseases significantly impacted patient outcomes. Timely initiation of vaccination and achieving full coverage among high-risk groups remain crucial public health priorities during epidemics and pandemics. Training healthcare personnel in private hospitals to enhance preparedness during outbreaks is essential. Lastly, implementing a referral system within primary healthcare services is critical for reducing the burden on hospitals and optimizing healthcare resource utilization.

Ethical Considerations

Compliance with ethical guidelines
The study was approved by the Ethics Committee of Guilan University of Medical Sciences, Rasht, Iran (Code: IR.GUMS.REC.1401.295).

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
Conceptualization and study design: Ali Davoudi Kiakalayeh, Zahra Mohtasham-Amiri; Data acquisition, analysis, and interpretation: Mehdi Karjooyan and Sajad Davoudi Kiakalayeh; Drafting of the manuscript: Ali Davoudi Kiakalayeh; Critical review of the manuscript for important intellectual content: Ali Davoudi Kiakalayeh; Statistical analysis: Sajad Davoudi Kiakalayeh; Supervision: Zahra Mohtasham-Amiri.

Conflicts of interest
The authors declared no conflict of interest.

References