The hygiene hypothesis and the COVID-19 pandemic

COVID-19, a highly contagious respiratory disease caused by the novel SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) primarily affects the respiratory tract but gastrointestinal symptoms (i.e. diarrhea, constipation, nausea) have also been reported in some patients.¹⁴

Preliminary studies have found that the gut microbiota is altered in patients with COVID-19 and that its composition correlates with infection severity, suggesting crosstalk between the gut microbiota and lung in response to SARS-CoV-2 infection.¹⁵

It should be noted that the changes in lifestyle adopted to curb the COVID-19 pandemic could also have a negative impact on the gut microbiome of uninfected individuals.¹⁶

These changes in hygiene, and a corresponding increased incidence of several autoimmune and allergic diseases,^18,19 have given rise to the hypothesis that they are causally linked (hygiene hypothesis). Notably, practices implemented to prevent the spread of COVID-19, such as physical distancing, frequent hand washing and sanitizer use, reduced travel and face mask wearing, will likely lead to further loss of key gut microbes.¹⁶

Taken together, the preventative health practices that have been implemented due to COVID-19 may exert collateral damage on the gut microbiome as well as long term health outcomes, particularly in children born just prior to or during the pandemic.¹⁶ Utilizing approaches known to enhance microbial diversity and support a healthy microbiota balance may prevent the negative health impacts associated with the enhanced hygiene practices implemented to prevent the spread of COVID-19.