Thread by @tmhohl71

1/n I am thinking about the various modes of #COVID19 transmission. Although not common, gastrointestinal symptoms are routinely reported by COVID patients. In humans, the SARS-CoV2 receptor ACE2 is not only found in alveolar epithelial cells (lung), but also in cells that line

2/n the small intestine, among other sites (heart and kidneys). Humans shed high levels of #COVID19 in the stool, a finding that raised the question whether fecal-oral transmission may occur. This would be very relevant for measures to limit the spread of disease.

3/n The concern for fecal-oral transmission is clearly outlined in this review. nature.com/articles/s4157…

4/n However, it is really important to distinguish microbiologic tests that quantify microbes on the basis on nucleic acids (DNA or RNA) and those that rely on microbial growth (viability). Tests that rely on quantitation of nucleic acids can detect a signal even if the microbe

5/n is no longer viable. In other words, a positive nucleic acid test does not necessarily equate the presence of a live, transmissible virus. A study published in Nature a few days ago illustrates this point. nature.com/articles/s4158…

6/n In this study, the authors found high viral shedding in the respiratory tract and in the feces of patients. This shedding was quantified by nucleic acid detection. It's the next experiment they did that was so valuable. The authors isolated virus from the respiratory tract

7/n and from the stool of patients and added it to human cells grown in culture. Live virus can infect these cells and destroy them. This finding is called a cytopathic effect and indicates the presence of a virus that can replicate.

8/n It turns out that #COVID19 isolated from respiratory specimens (lung, throat, nose) causes a robust cytopathic effect. This means that #COVID19 isolated from the respiratory tract is highly infectious. However, #COVID19 isolated from fecal specimens did not cause a cytopathic

9/n effect. It did not kill the human cells in culture. The authors interpreted this finding to signify that #COVID19 in the gastrointestinal tract is unlikely to be infectious. I agree. In effect, the authors performed a test that looks at the viability (and transmissibility) of

10/n #COVID19 from different human tissue sources. Lung + respiratory tract -> transmissible, contagious. GI tract, stool -> does not appear contagious. Thus, I believe that fecal-oral transmission of #COVID19 is not a major concern at this time. Kudos to Clemens Wendtner,

11/11 Christian Drosten and colleagues for a terrific study. This is the type of work that is driving #COVID19 science forward and helping us to develop better infection control guidelines to protect patients and HCWs. @sloan_kettering @ChariteBerlin #FlattenTheCurve