Detecting people with SARS-CoV-2 infection helps to reduce the transmission of the virus that causes COVID-19 disease, therefore to control the spread of the viral infection. For that purpose, there are different diagnostic tests for the detection of this disease. One of the most used, due to its specificity and high sensitivity, is the detection of the virus by PCR, in which the smear for the collection of the sample can be carried out using the following alternatives: oropharyngeal swab, nasal swab and nasopharyngeal swab ; Nasopharyngeal swab being the gold standard for detecting SARS-CoV-2.
Figure 1. Differences between nasal swab and nasopharyngeal swab
There is evidence that the precise identification of the virus is affected by the source of the samples. Thus far, it was known that the chances of obtaining a more accurate diagnosis were increased by collecting the sample using a nasopharyngeal swab compared to nasal or oropharyngeal swab. The difference between the different swabs lies in the place where the smear is made, to collect the sample While the nasal swab is done in the inferior turbinate; the nasopharyngeal swab it is carried to the back of the nostrils until it touches the wall of the pharynx; and the oropharyngeal swab is done in the back of the throat.
WHO has recommended nasopharyngeal swabbing as a gold standard for detecting SARS-CoV-2, based on several studies. This suggests that the use of nasopharyngeal swabs is a specific detection method, which provides greater sensitivity. However, a recent study published in the American Society for Microbiology compares the sensitivity between nasal samples and nasopharyngeal samples in a group of patients. These patients were subjected to molecular testing, using one nasopharyngeal swab and one nasal swab per patient. Finally, the study validates that the use of the nasal swab has a sensitivity almost equivalent to the nasopharyngeal swab.
In short, a high sensitivity and specificity in the detection of SARS-CoV-2 from nasal samples is evidenced, and it can be used instead of the nasopharyngeal swab in the identification protocol of the virus causing the COVID-19 infection, if you want to avoid the discomfort and irritation caused by this last procedure or the need for more specialized personnel in taking the sample.