1. Introduction:
Severe Acute Respiratory Coronavirus 2 (SARS-CoV-2), a newly identified coronavirus with size of 60–140 nm similar to SARS-CoV (approximately 80% similar), caused the most severe pandemic disorder of 21st century called COVID-19 (Lipsitch, Swerdlow, & Finelli, 2020; Malik et al., 2020). SARS-CoV-2 attaches to Angiotensin Converting Enzyme 2 (ACE2) receptor with 10–20 folds higher affinity than SARS-CoV (X. Xu et al., 2020). Today, massive antibiotic therapy is considered for some COVID-19 patients that result in more susceptibility to subsequent infections (Mak, Chan, & Ng, 2020); one of the most irritant complications is antibiotic-associated diarrhea (Wei et al., 2020). In this situation, probiotics may be a reasonable choice; they were defined as “Live microorganisms which when administered in adequate amounts confer a health benefit to the host” (Bahreini-Esfahani & Moravejolahkami, 2020). on the other hand, Probiotics have shown useful effects on treatment and prevention of viral infections (Mousa, 2017) due to the proven immunomodulatory activity and ability to stimulate interferon production; gut–lung axis explains the possible relations between respiratory disorders and gut microbiome (Marsland, Trompette, & Gollwitzer, 2015).
Recently, some COVID-19 patients showed microbial dysbiosis with decreased Lactobacillus and Bifidobacterium (K. Xu et al., 2020). Several different probiotics, including Lactobacillus acidophilus, Bifidobacterium and Saccharomyces boulardii , along with minerals & vitamins were given to a COVID-19 case; this type of nutritional support lowered the complication of massive antibiotic therapy (Horowitz, Freeman, & Bruzzese, 2020). As well, COVID-19-like symptoms disappeared after two days administration of oral probiotic in a 9 years-old boy (Ji et al., 2020). Results of a case series consist of 62 SARS-CoV2 infected patients in Zhejiang province were interesting; probiotics were administered as adjunct (X.-W. Xu et al., 2020). Other reports showed significant effect of probiotics; Compared to patients with non-severe disease, patients with severe disease had significantly more frequency to receive probiotics tablets (87.5% vs 40.4%, p=0.037) (Xiufeng Jiang et al., 2020). Results from another research suggested concurrent use of probiotics in COVID-19 patients to decrease the risk for Candida albicans (caused by prophylaxis with azithromycin) (Block, 2020).
Up to April 2020, two clinical trials have been registered regarding the probiotics supplementation in COVID-19 patients (Lythgoe & Middleton, 2020), however, more information is needed for designing research protocols. We tried to summarize the possible relationships between probiotics and viral infections especially SARS-CoV-2-related literature in this systematic review.