Background Earlier studies suggest that probiotics have protective effects in the prevention of respiratory tract infections (RTIs). Whether such benefits apply to RTIs of viral origin and mechanisms supporting the effect remain unclear. Aim To determine the role of gut microbiota modulation on clinical and laboratory outcomes of viral RTIs. Methods We conducted a systematic review of articles published in Embase and MEDLINE through 20 April 2020 to identify studies reporting the effect of gut microbiota modulation on viral RTIs in clinical studies and animal models. The incidence of viral RTIs, clinical manifestations, viral load and immunological outcomes was evaluated. Results We included 58 studies (9 randomized controlled trials; 49 animal studies). Six of eight clinical trials consisting of 726 patients showed that probiotics administration was associated with a reduced risk of viral RTIs. Most commonly used probiotics were Lactobacillus followed by Bifidobacterium and Lactococcus. In animal models, treatment with probiotics before viral challenge had beneficial effects against influenza virus infection by improving infection-induced survival (20/22 studies), mitigating symptoms (21/21 studies) and decreasing viral load (23/25 studies). Probiotics and commensal gut microbiota exerted their beneficial effects through strengthening host immunity. Conclusion Modulation of gut microbiota represents a promising approach against viral RTIs via host innate and adaptive immunity regulation. Further research should focus on next generation probiotics specific to viral types in prevention and treatment of emerging viral RTIs. Supplementary Information The online version contains supplementary material available at 10.1007/s00394-021-02519-x.

The mandatory classification of household waste forms the foundation and prerequisite for the waste recycle and reuse. This paper takes Xiamen’s local rule on the municipal household waste as a positivistic case, analyzes the results of the provision stipulating the mandatory obligation of household waste classification and the causes, and proposes relevant advices to improve the situation.