In the analysis of 1545 individuals who underwent high-resolution chest CT, 53% were men and 47% were women, with respect to the age range, it was significant in all age groups, with a predominance in the age groups between 30-39 and 60-69 years, being higher in the range of 50-59 years.

In the analysis of lung involvement, 32.45% were considered normal, 12.50% showed changes characteristic of other diseases and 55.05% showed changes characteristic of COVID-19. Regarding the degree of involvement, 37.70% had their pulmonary changes characterized as mild involvement (up to 25% of the lung area), 35.76% moderate (impairment of 25 to 50% of the lung area) and 26.54% severe (between 50 and 100% impairment of the lung area).

The age distribution of patients affected by covid-19 was predominantly from 30-39 to 50-59 years, with greater involvement between 50-59 years with 56% of patients classified between moderate (27.6%) and severe (28.0%).

We tested the null hypothesis of equal mean age in male cases and female cases versus the null hypothesis of different means with p 0.408 characterizing the difference between the sexes in relation to the patient's age in the evaluations performed.

The prevalence of COVID-19 was evaluated in relation to the female gender and age group considering the positivity in the PCR/CT scan result, observing a prevalence of 31.6% up to 30 years of age, in the 31 to 50 years range the prevalence was 35.6%, in the 51 to 70 years range it was 25.0% and over 70 years it was 28.0%. (table 7, chart 8)

In males, up to 30 years old was 26.7%, from 31 to 50 years old was 35.1%, from 51 to 70 years old was 32.1%, and above 70 years old was 40.0%. (Figure 7: (A7 and B7)

Images of multiple, unequal areas of ground-glass opacity and consolidation predominantly in the periphery of the lungs are characteristic manifestations at chest CT and are extremely useful in the early detection and diagnosis of this disease, aiding in the immediate diagnosis and eventual control of this global health emergency2. The lesions are mainly distributed in the lower lobes and in the peripheral zone, and most of the peripheral lesions are accompanied by localized pleural thickening adjacent to the subpleural region 91011121314.

Several entities may present with similar imaging patterns, predominantly ground-glass opaque, and within specific contexts, one should include in the differential diagnosis other infections by atypical agents including opportunistic agents (other viral agents, Mycoplasma pneumoniae, Pneumocystis jirovecii and others), inflammatory interstitial involvement of the lung parenchyma (organizing pneumonia, diffuse alveolar damage) determined by collagenosis, drugs or others15,16. However patients with fever and/or cough and conspicuous ground-glass opacity lesions in the peripheral and posterior lungs on CT images, combined with normal or decreased WBCs and a history of epidemic exposure, are highly suspected of having 2019 New Coronavirus (2019 -nCoV) pneumonia17 . Chest CT has high sensitivity for the diagnosis of 2019 coronavirus disease (COVID-19). Chest CT can be considered the main tool for current detection of COVID-19 in epidemic areas 18.

Routine CT for the identification of COVID-19 pneumonia is not currently recommended by most radiology societies19. According to the CBR, the diagnosis of COVID-19 should be based on clinico-epidemiological information associated with RT-PCR and/or serology20. However, the number of chest CT scans performed on people under investigation for COVID-19 has increased. We also anticipate that some patients will have incidentally detected findings that can be attributed to COVID-19 pneumonia, requiring radiologists to decide whether or not to mention COVID-19 specifically as a differential diagnostic possibility19.

Patients with fever and/or cough and conspicuous ground-glass opacity lesions in the peripheral and posterior lungs on CT images, combined with normal or decreased WBCs and a history of epidemic exposure, are highly suspected of having 2019 New Coronavirus (2019 -nCoV) pneumonia21. COVID-19 chest CT detection is very high among symptomatic high-risk individuals, especially with thin-section chest CT. The most common CT features in patients affected by COVID-19 included ground-glass opacities and consolidation involving the bilateral lungs in a peripheral distribution22.

Sensitivity and specificity may vary in different clinical populations, and prevalence is a marker of these differences. Clinicians are advised to base their decisions on studies that most closely match their own clinical situation, using prevalence to guide the detection of differences in study population or study design23.

Diagnostic accuracy plays a central role in the evaluation of medical diagnostic tests. Test accuracy can be expressed as sensitivity and specificity, as positive and negative predictive values, or as positive and negative likelihood ratios. Some feel that the positive and negative predictive values of a test are more clinically relevant measures than sensitivity and specificity. However, predictive values depend directly on the prevalence of the disease and therefore cannot be directly translated from one situation to another. In contrast, it is believed that the sensitivity and specificity of a test do not vary with disease prevalence 24.

Several studies suggest that CT should be a primary diagnostic tool for coronavirus disease (COVID-19), as they have reported sensitivities with CT that are much higher than that of the reverse transcriptase polymerase chain reaction (RT-PCR) test25. The development of faster laboratory tests may limit the role of CT in the diagnostic evaluation of COVID-19. However, baseline CT has other applications and that demonstrate that the extent of lung abnormalities by CT on admission were predictors of recovery in the intensive care unit26. A negative CT should not be used to exclude the possibility of COVID-19, especially early in the disease. Later in the course of the disease, the frequency of consolidation increases27.

In our study, all patients with clinical symptoms were between the 2nd and 6th days from the onset of symptoms, and, for this reason, HRCT was performed together with high-resolution chest CT scan.

The comparison between HRCT and HR-CRP showed a sensitivity of 68.8%, with specificity of 59.5%, accuracy of 91.5%, positive predictive value of 44.3% and negative predictive value of 80.0%, with a prevalence in the study of 31.9%. The significantly higher prevalence compared to that of the Federal District (12.9%)28at that time is due to the fact that the hospital unit is a reference and receives patients from all over the Federal District and surrounding areas.

Regarding risk factors for the worsening of a disease, a review showed that the most severe cases of the disease that evolved to pneumonia were older patients, male and with comorbidities, when compared to milder cases29. Being male was a factor associated with a higher risk of dying from COVID-19. Men had a lower probability of survival than women, as well as a 45% higher risk of death than women. A systematic review with meta-analysis including nine studies described that men represent 60% of patients with COVID-19, indicating a higher susceptibility for virus infection in this population30.

COVID-19 shows a difference in the case fatality rate between men (2.8%) and women (1.7%) 31. When analyzing the female sex we obtained a sensitivity of 55.5%, specificity of 59.3%, accuracy of 82.6%, positive predictive value of 37.1 and negative predictive value of 75.3% with a prevalence in the study of 30.3%. In the male gender analysis, we obtained a sensitivity of 81.6%, specificity of 59.8, accuracy of 100.0%, positive predictive value of 50.6% and negative predictive value of 86.8% with a prevalence of 33.6%. When we evaluate the effect of the sex with the age group, we observed in the female sex a stability of the sensibility in the diverse age groups with a drop above 70 years old and in the case of the male sex a sensibility that increases, reaching 100.0%, above 70 years old in the male sex.

The global case fatality rate for confirmed cases of COVID-19 is approximately 6.9%. Although it is difficult to compare lethality rates between countries due to the different stages of the outbreak, and other variations such as age of patients, health status of the population, and the healthcare systems within each country 34. The southern United States experienced regional outbreaks of COVID-19 in June. In these regions, increases in the percentage of positive SARS-CoV-2 test results among adults aged 20-39 years preceded increases among adults ≥60 years by a mean of 8.7 days (range = 4-15 days), suggesting that younger adults likely contributed to community transmission of COVID-1932 In the study, the specificity analysis always remained above 50% in both sexes reaching 70% in patients over 70 years and under 30 years.

In the municipality of VO (Italy), the prevalence of infection ranged from a central estimate of 1.2% to 1.7% up to age 50 years. Older participants showed a threefold increase in the prevalence of infection. Of the 81 participants positive for SARS-CoV-2 in the two surveys, 13 required hospitalization (16.0%). The age distribution was as follows: 1 (7.7%) aged 41-50 years, 1 (7.7%) aged 51-60 years, 4 (30.8%) aged 61-70 years, 5 (38.5%) aged 71-80 years, and 2 (15.4%) aged 81-90 years 33.

Disease severity and outcome appear to be highly correlated with age of onset, where the most severe forms of COVID-19 were seen for adults ≥ 55 years 34353637. Furthermore, an age-dependent mortality rate has been demonstrated with the lowest risk observed among those aged under 19 (0-0.1%) and 20-54 years (0.1-0.8%); however, the mortality risk gradually increases, affecting 1.4-4.9% in the 55-74 years age range, 4.3-10.5% among those aged 75-84 years, with the highest lethality rate of 10.4-27.3% in those aged ≥85 years ^{(34,36,37,38)}. Individuals with underlying health problems such as cardiovascular disorders, diabetes, liver and kidney disease, malignant tumors, or suppressed immune system seem to contract the severe form of the disease and the increased mortality rate343537. It is interesting that in the study, as of 45 years of age, we observed a decreasing p value, more significant up to 80 years of age, demonstrating the relevance of CT scanning as early as 45 years of age as an important tool in the diagnosis of COVID-19. In male individuals this sensitivity is higher and will certainly add to the clinical management to be taken. In the study we observed that the age averages vary in sensitivity and specificity, characterizing the importance of using high-resolution chest computed tomography in patients as a whole, because in new cases the patient does not present changes, and in cases with a higher age range the possibility of the occurrence of pulmonary changes will be increased. In Wuhan, China 2019, the mean age of patients was 47 years; 41.9% of patients were female. The most common symptoms were fever (43.8% on admission and 88.7% during hospitalization) and cough (67.8%). Diarrhea was infrequent (3.8). On admission, ground-glass opacity was the most common radiological finding on chest computed tomography (CT) (56.4%). No radiographic or CT abnormalities were found in 157 of 877 patients (17. 9%) with non-severe disease and in 5 of 173 patients (2.9%) with severe disease39.

As COVID-19 spreads to areas with large cosmopolitan populations, understanding how ethnicity affects COVID-19 outcomes is essential40. Blacks and ethnic minorities may be at higher risk for acquisition, disease severity, and poor outcomes on COVID-19 for several reasons. Specific ethnic groups, such as South Asians, have higher rates of some comorbidities, such as diabetes, hypertension, and cardiovascular disease, which have been associated with severe disease and mortality in COVID-1941. Ethnicity may interact with the spread of the virus through cultural, behavioral, and social differences, including lower socioeconomic status, health-seeking behavior, and intergenerational cohabitation40. We found significant differences in the number of reported contacts by age, gender, race, and ethnicity. Certain demographic groups, including people younger than 45, black and Hispanic men and respondents, have significantly higher contact rates than the rest of the population. Tracking changes in interpersonal contact patterns can provide rapid assessments of the impact of physical distancing policies during the course of the pandemic and help identify populations at risk42.

Knowledge of populations at higher risk of worsening and death from the disease is of utmost importance and is part of therapeutic strategies to prevent worsening of the disease in these populations43. In Distrito Federal, the prevalence of the Coronavirus disease varied from place to place, having its highest prevalence in Sobradinho with 12.82%28. The risk of contracting a directly transmitted infectious disease, such as Coronavirus Disease 2019 (COVID-19), depends on who interacts with whom. These person-to-person interactions vary by age and location-for example, at home, at work, at school, or in the community-due to different social structures. These social structures and contact patterns vary between and within countries. Although social contact patterns can be measured through surveys, most countries around the world, especially low and middle income countries, lack nationally representative contact surveys44.

There was good sensitivity and accuracy between CT scan and RT-PCR, highlighting that RT-PCR is difficult to perform, and that its detection rate is affected by several factors, such as sampling, storage, and reagent performance, and that in our reality this may have affected the results obtained, reducing this sensitivity obtained by the frequent occurrence of false negatives.

There was significant accuracy of CT scan in symptomatic patients suspected of COVID-19, highlighting that the sensitivity increases with age and in men, more prevalent in the pathology. Considering the prevalence, in low prevalence sites, normal CT scans almost rule out the pathology, whereas in high prevalence sites or situations, we have demonstrated that the presence of pulmonary alterations confirms the disease.