The hygiene hypothesis and the COVID-19 pandemic

Covid-19

by Dr Genelle Healey

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Dr Genelle Healey, PhD

Created 23 November 2021

Updated 07 February 2022

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

Over the last few decades, a significant reduction in microbial diversity and the overt extinction of ancestral microbes has occurred due to improvements in hygiene (e.g. hand washing and sanitizer), modern medications (e.g. antibiotics) and urban living.¹⁷

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.

Sources

^{14 Gupta A, Madhavan MV, Sehgal K, et al. Extrapulmonary manifestations of COVID-19. Nat Med. 2020 Jul;26(7):1017-1032.}

^{15 Zuo T, Zhang F, Lui GCY, et al. Alterations in Gut Microbiota of Patients With COVID-19 During Time of Hospitalization. Gastroenterology. 2020 Sep;159(3):944-955.e8.}

^{16 Finlay BB, Amato KR, Azad M, et al. The hygiene hypothesis, the COVID pandemic, and consequences for the human microbiome. Proc Natl Acad Sci U S A. 2021 Feb 9;118(6):e2010217118.}

^{17 Blaser MJ, Falkow S. What are the consequences of the disappearing human microbiota? Nat Rev Microbiol. 2009 Dec;7(12):887-94.}

^{18 Lambrecht BN, Hammad H. The immunology of the allergy epidemic and the hygiene hypothesis. Nat Immunol. 2017 Sep 19;18(10):1076-1083.}

^{19 Murdaca G, Greco M, Borro M, et al. Hygiene hypothesis and autoimmune diseases: A narrative review of clinical evidences and mechanisms. Autoimmun Rev. 2021 Jul;20(7):102845.}

Microbiota, a diplomatic immunity?

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The hygiene hypothesis and the COVID-19 pandemic

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Over the last few decades, a significant reduction in microbial diversity and the overt extinction of ancestral microbes has occurred due to improvements in hygiene (e.g. hand washing and sanitizer), modern medications (e.g. antibiotics) and urban living.¹⁷

Microbiota, a diplomatic immunity?

Introduction

Intestinal Immunity

Gut microbiota influences respiratory immunity

Role of the microbiota in skin immunity and atopic dermatitis

Conclusion

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The hygiene hypothesis and the COVID-19 pandemic

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About this article

Author

Over the last few decades, a significant reduction in microbial diversity and the overt extinction of ancestral microbes has occurred due to improvements in hygiene (e.g. hand washing and sanitizer), modern medications (e.g. antibiotics) and urban living.17

Microbiota, a diplomatic immunity?

Introduction

Intestinal Immunity

Gut microbiota influences respiratory immunity

Role of the microbiota in skin immunity and atopic dermatitis

Conclusion

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Over the last few decades, a significant reduction in microbial diversity and the overt extinction of ancestral microbes has occurred due to improvements in hygiene (e.g. hand washing and sanitizer), modern medications (e.g. antibiotics) and urban living.¹⁷