## 3 Results and Discussion
### Viral Load  
Despite the biological sample origin and detection methods, SARS-CoV-2 viral load is a key parameter for virus detection and infectiousness evaluation and risk assessment. Previous studies observed that SARS-CoV-2 viral load is significantly higher in sputum when compared to throat swabs and nasal swabs (17,429 \(\pm\) 6920 copies/test, 2552 \(\pm\) 1965 copies/test, \(p\) < 0.001 and 651 \(\pm\) 501 copies/test, \(p\) < 0.001, respectively) and that viral loads detected in the early and progressive stages of the infection were significantly increased than that in the recovery stage [63]. It is described that viral load kinetics as well as viral shedding duration are key determinants for disease transmission and must be taken into consideration when selecting a biological sampling method. Previous studies have reported that the peak of SARS-CoV-2 titres in the upper respiratory tract occurs in the first week of illness. On the other hand, despite the fact that SARS-CoV-2 RNA shedding in respiratory and stool samples can be prolonged, virus viability may be brief [64]. On the other hand, [PERSON] et al. demonstrated that in SARS-CoV-2 RT-PCR detection the mean cycle threshold values for blood, sputum, faeces, urine, bronchoalveolaravaler lavage fluid and fibro bronchoscope brush biopsy were more than 30 (<2.6 \(\times\) 10\({}^{4}\) copies/mL), while for nasal swabs authors obtained a mean cycle threshold value of 24.3 (1.4 \(\times\) 10\({}^{6}\) copies/mL), which is indicative of a higher viral load. Thus, it is clear that the testing of specimens from multiple sites is preferable in order to increase the test sensitivity and decrease false-negative results [65]. Furthermore, reports regarding rapid antigen tests (RATs) for COVID-19 based on lateral flow technology demonstrated that even the most sensitive RAT was not able to detect SARS-CoV-2 in the samples containing small amounts of virus [66]. Additionally, despite the fact that for the RT-PCR methodology, the sensitivity of rectal stools/swab, urine, and plasma is inferior to sputum and that RT-PCR remains the gold standard for the diagnosis of SARS-CoV-2, the combination of different diagnostic tests has been highly recommended to obtain proper sensitivity and specificity [67]. Currently, SARS-CoV-2 detection can be performed utilizing techniques such as reverse-transcription loop-mediated isothermal amplification (RT-LAMP), enzyme-linked immunosorbent assay (ELISA), lateral flow assay (LFA), chemiluminescent immunoassay (CLIA), and neutralization assay and new technologies such as sensor-based or CRISPR applications are also been developed for the rapid detection of SARS-CoV-2 [68]  
Overall, our results demonstrated that NPSs, OPS, and BAL have the maximum score in RNA Extraction Type. However, BAL has high associated costs. Concerning sputum and saliva, all the aspects were evaluated with a score of 5.0 except for RNA Extraction Type in sputum. Regarding the total scores of the multiple specimens, the lowest corresponds to BAL with a score of 1.7, followed by blood with 3.1 and NPSs and OPSs with 3.6 and 3.7, respectively. Urine and faeces have the same value, 4.4, sputum has 4.9, and the highest and maximum possible corresponds to saliva with 5.0, making this last specimen the most suitable one in all aspects to proceed COVID-19 diagnosis. Nevertheless, it is important to note that this biological sample also imposes risks for health personnel with occupational direct contact [69]. Importantly, even though SARS-CoV-2 testing has currently decreased, other respiratory viruses are still very active, particularly in children, including respiratory syncytial virus (RSV), influenza and parainfluenza viruses, and adenoviruses, among others. Even though these infections are usually diagnosed clinically based on symptoms and local epidemiology, the identification of the specific pathogen may affect clinical management and be crucial for containing potential outbreaks [70].