The Week That Wasn't in COVID-19: Stool Surveillance, Smoking, 11-Days Infectious

Ellie Kincaid

May 29, 2020

This week in COVID-19 news, scientists quantified the presence of SARS-CoV-2 in Connecticut sewage, there were more headlines about fewer smokers getting hospitalized, and the number of days after which COVID-19 patients are no longer infectious was specified as 11. But you didn't see these headlines on Medscape. Here's why.

Stool Surveillance

Measuring the presence of genetic material from SARS-CoV-2 in sewage could be a tool to predict local outbreaks or support decisions to ease restrictions, researchers from Yale University propose in a preprint. The scientists measured the concentration of RNA from SARS-CoV-2 in primary sewage sludge from a treatment plant in New Haven, Connecticut and compared their measurements to data on local COVID-19 cases and hospitalizations. They found that the changes in SARS-CoV-2 RNA concentration in the sludge over the course of the local outbreak closely matched the curves of the case and hospitalization data, but the sewage data "was a leading indicator" by 7 and 3 days, respectively. 

This research is an ingenious application of the knowledge that people with COVID-19 shed the coronavirus in their stool, and the methods indeed could be useful in outbreak surveillance. But because the research hasn't been peer-reviewed yet, and it doesn't have clear implications for clinical practice, we didn't think it was vital information for our readers.  

Smoking, Again

A new preprint from Italian physicians notes that the prevalence of smoking is lower in hospitalized COVID-19 patients than in the general population, and it's not the first. "The current study suggests that smokers might carry some type of protective mechanism from symptomatic SARS-CoV-2 infection," the authors write, "although this should be confirmed in specifically-designed, controlled studies."

Again, this preprint hasn't been peer-reviewed yet, and the observational data it presents cannot establish causal relationships. The pattern the researchers are tracing is certainly interesting from a scientific perspective to pursue novel treatments for COVID-19, but it's not yet clear what to make of such observations. Because they shouldn't change practice — clinicians won't advise patients to start smoking because of a theoretical protective mechanism for one disease — we didn't write a story about this preliminary report. 

COVID-19 Patients Not Infectious After 11 Days 

The headline statement that "COVID-19 patients are not infectious 11 days after getting sick" comes from a report from Singapore's Academy of Medicine, National Centre for Infectious Diseases and Chapter of Infectious Disease Physicians summarizing available data on the period during which people with symptomatic COVID-19 could spread infectious SARS-CoV-2 to others. 

Specifically, the "11 days" figure comes from the report's description of a study of 73 COVID-19 patients in which researchers could not isolate or culture virus from the patients "after day 11 of illness." This is consistent with epidemiologic data, the report states, and indicates that "while viral RNA detection may persist in some patients, such persistent RNA detection represents non-viable virus and such patients are non-infectious." 

The Singapore report's summary of available data on the infectious period of COVID-19 patients is useful, but it does not cite the study from which the "11 days" figure comes, so the source for the number — and any scientific limitations of the observation –– are unclear. Zeroing in on a specific number of days, rather than a range, for a COVID-19 patient's infectious period is unlikely to be accurate for every patient, probably isn't what the underlying study did, and therefore isn't useful for clinicians. The overall point that positive results from PCR tests for SARS-CoV-2 RNA do not mean a person is still infectious is a good one; however, we covered this based on other data

Ellie Kincaid is Medscape's associate managing editor. She has previously written about healthcare for Forbes, the Wall Street Journal, and Nature Medicine. She can be reached at or @ellie_kincaid on Twitter.

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