A review of nasopharyngeal swab and saliva tests for SARS‐CoV‐2 infection: Disease timelines, relative sensitivities, and test optimization

Abstract

Testing is an essential part of containment of the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pandemic. This review summarizes studies for SARS‐CoV‐2 infection and testing. Nasopharyngeal samples are best at sensitivity detection, especially in early stages of disease and in asymptomatic individuals. Current swab processing involves a 100‐ to 1000‐fold dilution of the patient sample. Future optimization of testing should focus on using smaller volumes of viral transport media and swab designs to increase comfort and increased viral adhesion.

INTRODUCTION

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) was first reported by the World Health Organization (WHO) in December 2019 in China. By January 1, 2021, the coronavirus dis- ease 2019 (COVID‐19) amounted to 83.9 million cases and 1.8 mil- lion deaths worldwide,¹ with the United States accounting for 25% of the total cases.² The virus is transmitted via small liquid aerosols or larger respiratory droplets that are released by breathing, talking, sneezing, or coughing. SARS‐CoV‐2 enters the body when small, airborne viral particles contact a person’s mouth, eyes, or nose.

The SARS‐CoV‐2 virus is particularly dangerous because it can persist asymptomatically in individuals for up to 14 days, providing substantial opportunity for undetected transmission.³ Lives can be saved by identifying and isolating those infected through accurate testing at an early stage. Many different tests for SARS‐CoV‐2 have been advanced for clinical use, which vary from intranasal pharynx swab tests administered by trained healthcare providers to self‐ administered saliva tests. In this review, we summarize available knowledge of the pathophysiology of this disease and data for commonly administered tests, to determine the best current

practice. The goal is to highlight potential areas for improvement in testing to bring more sensitive, accurate, and comfortable tests for future use in detecting SARS‐CoV‐2 and other upper respiratory infections.

METHODS

PubMed, Web of Science, and Google Scholar were searched for papers published between September and November 2020. Keywords included: “COVID‐19,” “coronavirus,” “SARS‐CoV‐2”, “asymptomatic”, “saliva test”, “nasopharyngeal swab”, “COVID swab”, “ACE 2 cell infection”, “viral load,” and variations.

Papers were screened for relevance based on if they listed the relative sensitivities of various tests, dealt with symptomatic/asympto- matic patients, and provided sufficient details of the study. References in chosen studies were also searched for other relevant studies.

In addition to databases, preprints and hospital bulletins were also consulted. Documents and guidelines from international orga- nizations, such as WHO, and national institutions, such as the Center for Disease Control (CDC) and the Food and Drug Administration