A positive nasopharyngeal swab is when neo-coronavirus RNA is detected in a specimen collected through a pharyngeal swab.

Nasopharyngeal swabs are the predominant method of specimen collection

According to the HSC guidelines, pathogenic testing is primarily done by real-time fluorescence-polymerization chain reaction (RT-PCR) or/and "next-generation" sequencing technology to detect neointestinal RNA in specimens such as nasopharyngeal swabs, sputum and other lower respiratory secretions, blood, and stool.

The guidelines include a statement that "lower respiratory specimens are more accurate". This statement was made in the context of repeated negative nasopharyngeal swabs in critically ill patients who were diagnosed with viral RNA from specimens collected from the lower respiratory tract.

In a comprehensive view now, this statement is not accurate.

In fact, many cases have only upper respiratory tract infection and no lower respiratory tract infection. Therefore, for the overall picture, collection of upper respiratory specimens is rather more accurate; only in some severe cases, where upper respiratory specimens do not detect the virus (negative), collection of lower respiratory specimens has the potential to improve the detection rate.

Importantly, from several specimens, upper respiratory specimens are the most convenient to collect, easier to manipulate, non-invasive and more acceptable.

How is an upper respiratory tract specimen collected?

It is by using a nasopharyngeal swab in the nasal cavity and pharynx to obtain exfoliated cells and viral particles from these areas, which are then tested.

The so-called nasopharyngeal swab is a long cotton swab.

This swab is inserted through the nasal or oral cavity into the pharynx for sample collection.

The samples collected in this way are called nasopharyngeal swab specimens and oropharyngeal swab specimens, respectively.

Theoretically, nasopharyngeal swab samples have a higher virus detection rate than oropharyngeal swabs.

However, nasopharyngeal swabs are too irritating for many people to tolerate; in contrast, oropharyngeal swabs are more easily accepted.

This is the reason why more oropharyngeal swab specimens are collected in China.