Stomach bug or COVID?

Some physicians and public health officials are warning about an uptick in patients with gastrointestinal symptoms that may be linked with the highly contagious Omicron subvariant BA.2. But with many countries abandoning pandemic precautions and testing, it’s hard to separate these cases from resurgences of other illnesses.

Chuck Wurster, an emergency physician in Edmonton, is one of several Canadian and American clinicians on social media who have noted unusual numbers of patients seeking care for nausea, vomiting and diarrhea in recent weeks. “Would not be surprised if this surge is being driven by Covid,” he tweeted.

According to Kami Kandola, chief public health officer for the Northwest Territories, some people recently infected with SARS-CoV-2 are reporting diarrhea as their only symptom, and those who only experience gastrointestinal symptoms may be less likely to test positive on rapid tests using a nasal swab.

However, a spokesperson for the territory’s COVID Secretariat told CMAJ that they don’t have the capacity to track or quantify such cases, and Kandola may be speaking anecdotally.

Zain Chagla, an infectious disease physician in Hamilton, Ontario, has noted a similar uptick in patients with COVID-19 and gastrointestinal illness. “There seem to be a lot of profound GI symptoms,” he said. “Certainly, for some folks, their only presentation was really severe GI and a little bit of fever.”

“We have seen that different variants can often have different symptom presentations,” Chagla said. “There’s always been some gastrointestinal illness associated with COVID, especially in younger populations… but it seems to be coming back now.”

The trend is one to watch, especially as BA.2 is rapidly displacing the original Omicron strain to become the dominant variant in Canada.

At the same time, “there is probably co-circulation of the typical things that cause GI illnesses as well, like Norwalk, rotavirus, and enterovirus,” Chagla said. “They seem to also be circulating now, based on some of the samples we’ve seen come to our lab.”

A spokesperson for Ottawa Public Health noted they have documented 13 outbreaks of gastroenteritis in the city since the beginning of February, in some weeks surpassing the historical three-season average for educational and health care settings.

Meanwhile, Vancouver Coastal Health has seen an increase in norovirus cases associated with the consumption of raw oysters, but not COVID.

Nisha Thampi, a pediatric infectious disease physician at the Children’s Hospital of Eastern Ontario, said norovirus has made a comeback this year after negligible cases during earlier waves of the pandemic. “We’re seeing cases among staff and patients at CHEO, and I think that comes with relaxation in public health measures,” she said.

Throughout the pandemic, Thampi has also seen children test positive for SARS-CoV-2 whose only symptoms were vomiting or diarrhea, and who didn’t have other gastrointestinal infections.

Patchy testing for both SARS-CoV-2 and gastrointestinal pathogens can make it tough to know which is behind the recent anecdotal reports, she says. In the case of BA.2, “we can’t see if more kids are presenting with gastro [symptoms] compared to earlier variants because we’re not testing as comprehensively as we were before.”

And according to Dr. Gerald Evans of Ontario’s COVID-19 Science Advisory Table, “we don’t investigate people with GI illnesses extensively like we have been doing the last two years with respiratory infections.”

“The other problem is that it’s really difficult [to test] if the BA.2 variant is suddenly causing a GI illness,” Evans added. “We test people by sampling [from] their respiratory tract, and if this is now dominating as an enteric pathogen, then maybe we’re not detecting it.”

“Maybe we need to do some stool testing for COVID, [as well as] looking for these other viruses,” he said.

Canada isn’t the only country reporting a dual surge in BA.2 and gastrointestinal symptoms. In the United Kingdom, some doctors say they’re seeing more patients with COVID-19 experiencing vomiting and diarrhea that lasts “for days” — in contrast to other gastrointestinal illnesses, which typically last one or two days.

In May, National Health Service hospitals warned people not to visit if they have COVID or an upset stomach, as outbreaks of SARS-CoV-2 and norovirus have forced some institutions to close hundreds of beds.

According to the UK’s ZOE COVID study, which analyzes the self-reported health data of 4.7 million users of a nutrition app, there was a “sharp increase” in the number of people reporting GI symptoms from mid-December 2021 through January 2022.

Looking at users’ PCR test results, researchers found that a “significant proportion” of people reporting GI symptoms tested positive for SARS-CoV-2. However, “we also saw an increase in the proportion of people with these symptoms who tested negative,” said Tim Spector, a professor of genetic epidemiology at King’s College London. These preliminary findings suggest that “even though Omicron can be associated with GI symptoms, the rates are not higher than what we saw with Delta.”