## 3 Results and Discussion
### Respiratory System  
Published RT-qPCR assays have demonstrated excellent analytical sensitivity and specificity for respiratory samples. However, false-negative tests remain a concern, especially in patients who have distinctive symptoms of SARS-CoV-2 infection in high-prevalence settings or who have consistent findings on chest imaging that lead to the suspicion of viral pneumonia. In the case of NPSs, a false negative result can be a consequence of several factors, such as poor quality of collection, test performance during the incubation period, or sample processing errors [23]. As previously mentioned in the introduction, the specimens currently recommended and used for the diagnosis of COVID-19 are from the upper respiratory system, in particular NPSs and/or OPS. The collection of these types of samples requires a proximity between the patient and the healthcare professional that naturally increases the risk of infection for both [8], having a score of 3.0 assigned in these two parameters. In addition, the two types of samples are considered invasive, and the collection may imply several adverse effects to the patient that may span from discomfort to more serious complications. As far as OPS is concerned, it consists of collecting biological material from the region of the palatine tonsils and the posterior wall of the orophynx [24]. For this purpose, the patient must completely remove their mask and open their mouth wide enough [8; 25]. Besides being uncomfortable for the patient, the collection may induce the gag reflex, leading to reduced participation and compliance [8; 26]. In addition, completely removing the mask implies an increased risk for the healthcare professional, as not only does the collection require proximity but it also involves the removal of personal protective equipment on one side. Unlike the OPS, in the nasopharyngeal specimen collection, it is possible for the patient to partially remove the mask, exposing only the nose [25]. However, even with this advantage, this collection is still considered more invasive when compared to the OPS, essentially due to the complications to which is associated: not only does it trigger some reflexes, such as sneezing and/or coughing, but it may also cause epistaxis and other minor adverse effects, such as nasal discomfort, headache, earache and rhinorhoea [27; 28]. So, because of that, when it comes to the collection criteria, NPS is rated as 3.0 and OPS as 4.0, as is seen in Table 1. These complications are due to nasal mucosa being extremely fragile, sensitive, and very vascularized; therefore, there is a tendency for mild bleeding as a consequence of superficial trauma [28]. In addition to this natural sensitivity of the mucosa, patients infected with SARS-CoV-2 also have greater fragility, since the upper respiratory system is inflamed, leading to more prominent bleeding, as may happen in patients with rhinitis and sinusitis [28; 29]. In both samples, the reflexes induced by the collection may originate droplets, possibly endangering the healthcare professional responsible for the procedure; this transmission is favoured by the total or partial removal of the patient's mask [30]. However, according to [PERSON] (2020), several studies have shown that there is a more prolonged detection by RT-qPCR in specimens from the lower than from the upper respiratory system [23]. This would lead us to choose a collection from the lower respiratory tract, but several factors need to be meticulously evaluated to conclude which type of sample best suits the patient and the workflow of each hospital and laboratory. Among the many factors that influence the choice of the specimen are the invasiveness of the collection and the risk of infection to the patient and healthcare worker. Several studies have looked for methods to decrease all associated risks, searching for a balance between a less invasive collection procedure and the obtainment of high-quality samples.