DISCUSSION
Our study included 271 patients aged 18–65 years with positive RT-PCR tests for COVID-19 who had symptoms for longer than 5 days at the time of admission. Smoking and the presence of HT were found to be statistically significant in the group that developed pneumonia. Hospitalisation, the need for additional antibiotics, desaturation and bilateral involvement of the lung parenchyma were more common in the pneumonia group. Of the laboratory parameters, initial D-dimer, troponin, neutrophil, NLR, CRP, LDH and ferritin levels were higher in the pneumonia group, and lymphocyte, albumin and haemoglobin values were lower. Older age, presence of HT, dyspnea at hospital admission, low albumin and high troponin were found to be risk factors for the development of pneumonia. Studies have shown that the need for mechanical ventilators, intensive care hospitalisation and death rates are significantly higher in COVID-19 patients over 65 years of age compared to younger patients (6, 7). However, no specific data for the clinical features and treatment of young adult COVID-19 patients admitted to hospitals have been published. As far as we know, although studies on COVID-19 patients under the age of 65 have been published, no comparative studies between young adult patients with and without pneumonia have been published. In a study of patients under the age of 50 with a diagnosis of COVID-19, 56% of the patients were male, their mean age was 44.44 years, and 92.1% had CT lung involvement (3). Our study found that pneumonia developed at a rate of 67.9%, with a mean age of 46.48 ± 11.99 years. In another study, where a median age of 50 years (IQR; 40–68) was found in a pneumonia group, it was stated that older age was a significant risk factor for the development of pneumonia (8). In Jung et al.’s (9) study, the mean age of a group of patients who initially developed pneumonia or during a follow-up was significantly higher (51.5 and 54.9 years, respectively) compared to a group without pneumonia (38.5 years). In our study, in accordance with the literature, the median age was 51 years (IQR; 41.5–58) in the group that developed pneumonia, and older age was statistically significant for the development of pneumonia. In the literature, it has been stated that HT, CVD, DM and smoking are associated with poor clinical outcomes of COVID-19 cases (10, 11). In our study, the most common comorbidities detected in the pneumonia group were HT, DM and CVD, and there was a significant relationship between smoking and the development of pneumonia. The most commonly reported symptoms observed in COVID-19 patients are fever, cough and myalgia (12, 13). In our study, these symptoms were common in the pneumonia group, but only dyspnea was statistically significantly associated with COVID-19 pneumonia. Fever, the most common COVID-19, was not found to be significant in our study, suggesting that it was not a predictor for pneumonia. In another study, approximately 63% of hospitalised COVID-19 patients under the age of 65 had desaturation, and the hospital stay was longer in this group (14). In our study, desaturation and hospitalisation were statistically more significant in the pneumonia group. To date, most studies on prognostic markers have shown an increase in D-dimer and LDH values and a decrease in lymphocyte levels (15, 16), and Zhang et al. (17) emphasised that D-dimer levels are an important marker for determining mortality in cases with COVID-19 pneumonia. Itelman et al. (18) emphasised that patients with severe COVID-19 have higher leukocyte and neutrophil counts and LDH levels. In our study, increased D-dimer and LDH and decreased lymphocyte levels were found to be statistically significantly higher in the pneumonia group. NLR, high CRP and low albumin have high sensitivity and specificity for demonstrating inflammation. Studies have shown that the NLR and the CRP/lymphocyte ratio are independent prognostic markers for many diseases (19, 20). In our study, while the NLR and initial CRP values were high in patients with pneumonia, albumin and lymphocyte values were lower. In a retrospective cohort study involving 191 patients with COVID-19 from Wuhan, China, high LDH and ferritin levels were associated with mortality (21), and Wang et al. (22) reported that 40% of patients with COVID-19 had high LDH values at the time of admission. In a systematic review conducted by Taneri (23), including 189 studies and 57,563 patients, compared to patients with intermediate or low risk of disease, high ferritin and low haemoglobin levels were found in patients with high risk for severe disease (23). Cobre et al. (24) also found that high ferritin and low haemoglobin levels were observed in both COVID-19 patient groups and patients with severe disease (24). In our study, while haemoglobin levels were lower in the group that developed pneumonia, ferritin and LDH levels were higher. In a systematic review of four studies, including 374 patients, troponin levels were observed to be significantly higher in patients with severe COVID-19 infection compared to non-serious patients (25). Zhu et al.’s (15) study also found that troponin values were a prognostic marker for severe disease. In our study, troponin values were higher in the group with pneumonia, and they were found to be a statistically significant risk factor for the development of pneumonia. In various studies, increased liver function markers, particularly ALT, AST, gamma-glutamyl transferase and total bilirubin levels, have been described in COVID-19 patients (26, 27). However, no statistical difference was found in these values in our study. In one study, at the time of diagnosis, 203 patients had bilateral pneumonia, 39 patients had unilateral pneumonia, 6 patients had normal thorax CT scan results and 163 (65.7%) had radiological progression of symptoms on the 7th day in repeated radiological imaging (28). In another study, patients with or without pneumonia at the time of diagnosis had negative or positive CT findings according to the duration of symptoms; it was stated that the presence of pneumonia varied depending on the time after symptom onset, and the non-pneumonia group was characterised by younger patients, normal laboratory findings, and less comorbidity (9). In another study, it was stated that positive CT findings were associated with symptom duration, and 56% of patients showed normal CT findings in the early phase (0–2 days) after symptom onset (29). Patients with symptoms for more than 5 days were included in our study, and in accordance with the literature (30), bilateral involvement was more common in the group with pneumonia, and older age was considered a risk factor for the development of pneumonia.