The microbiota and its effect on health has been extensively studied over the past decade. In many studies, the term microbiota has become synonymous with the bacterial component of the microbiota. Other microbes in the microbiota, such as viruses and fungi, have been neglected until recently. This special issue provides some background on the mycobiota and explores the role of gut fungi in human diseases such as cancer, metabolic diseases, and infection by Clostridiodes difficile, and describes the incidence of fungal infections in transplant patients. The mycobiota, once overlooked, now garners increasing attention.

Most patients with severe complications from COVID-19 have underlying conditions such as obesity, diabetes, and hypertension. In parallel, there is growing evidence for a link between periodontitis and non-oral systemic diseases. The oral cavity is also a reservoir for respiratory pathogens, and patients with periodontal disease are more likely to develop hospital-acquired pneumonia than healthy individuals. We therefore hypothesize that improving oral health could decrease the severity of COVID-19 symptoms and reduce the associated morbidity.

Coronaviruses, including SARS-CoV-2, have caused pandemics in the past two decades. The most prevalent SARS-CoV-2 variants of concern can re-infect individuals who have been previously infected with other variants or had protection from vaccines targeting the original SARS-CoV-2 variant. Given the high risk of transmission of coronavirus via aerosols produced during dental procedures, it is important to understand the future risk of coronavirus infection for oral health professionals and to diagnose quickly early stages of outbreaks. Testing of saliva for coronavirus may be the least invasive and most convenient method for following the outbreak at the individual and community level. This review will describe strategies for diagnosis of coronavirus in saliva.