What we know so far

Respiratory symptoms, such as coughing or breathing problems, are the most common symptoms of COVID-19.

But early reports from China made it clear that COVID-19 could also cause symptoms of GIT. The GI system contains:

• the mouth
• esophagus, the tube that connects to the stomach
• stomach
• small intestine
• the anus

The first person with a confirmed COVID-19 in the United States also experienced nausea and vomiting for two days before developing diarrhea. And one of the earliest U.S. studies found that about 32% of patients with the disease experience diarrhea, nausea, or loss of appetite.

The research is evolving. However, according to a review published in 125 articles and a total of 25,252 patients, the most common GIT symptoms associated with COVID-19 are:

• lack of appetite (19.9%)
• lack of smell or taste (15.4%)
• diarrhea (13.2%)
• nausea (10.3%)
• vomiting of blood or gastrointestinal bleeding (9.1%)

Another review published in late January found much wider variations in the incidence of symptoms, such as:

• diarrhea (9-34%)
• nausea, vomiting or both (7–16%)
• abdominal pain (3–11%)

Less commonly, COVID-19 can also cause:

The disease can also destroy intestinal tissue and reduce bowel movement.

At present, it seems that most people who experience GI symptoms with COVID-19 develop it along with respiratory symptoms.

A late 2020 survey found that about 20% of people with COVID-19 infections experience GI symptoms only. And sometimes these symptoms develop before respiratory symptoms or fever develop.

Early studies suggest that GI symptoms usually occur in the early stages of the infection. But more research is needed to confirm when GI tract symptoms develop in COVID-19 cases when there is a specific time frame.

Researchers are still learning more about how infection with SARS-CoV-2 affects different parts of the body.

There is evidence that SARS-CoV-2 can infect cells in the respiratory tract and GIT, as well as cells elsewhere in the body.

Most studies show that the SARS-CoV-2 virus invades intestinal cells, or enterocytes, and respiratory cells by using the angiotensin-converting enzyme 2 (ACE-2) protein as a receptor. The ACE-2 receptor is embedded in cellular membranes. It helps regulate blood pressure by controlling the levels of the protein angiotensin, which encourages blood vessels to lower and increase blood pressure.

The virus enters intestinal cells after binding its characteristic vein proteins to ACE-2. Once inside the cell, the virus uses the cells’ own machinery to produce copies of viral proteins and ribonucleic acid (RNA). RNA is the genetic material of retroviruses, such as SARS-CoV-2, much like human DNA.

When SARS-CoV-2 particles leave an infected cell, it causes the release of cytokines, small proteins that play a role in inflammation. This process can cause GI tract symptoms.

GI symptoms can also occur if viruses destroy or damage GIT tissues, especially pain, nausea and diarrhea. Some research shows that COVID-19 can also alter the intestinal microbiota, the community of microbes that normally live in the gut or stomach.

Once in the GI tract, the virus can also move through the portal vein, the vein that draws blood from the digestive tract. This can cause viruses to affect the vagus nerve, causing nausea.

Nausea and diarrhea are also common symptoms of medications that health professionals often use to treat COVID-19, such as antivirals and antibiotics.

There is increasing evidence that SARS-CoV-2 can transmit to others via fecal-oral transmission. This means that people can contract infection by accidentally ingesting or inhaling droplets of infected feces.

In fact, fecal samples from the first person with confirmed COVID-19 in the US contain virus particles. Other coronaviruses can also cause viral shedding, with reference to the release of viral particles in feces.

Some research even suggests that humans may shed viral particles in their feces after the virus is not noticed in the upper respiratory tract, such as the lungs, nose or throat.

If true, it can change how someone can spread the virus to others and for how long. But researchers have yet to determine if the proteins and particles shed in feces are contagious or can actually cause disease.

People who experience GI symptoms with COVID may be more likely to develop adverse health complications or risks.

A November 2020 study found that experiencing these symptoms had the risk associated with developing acute respiratory distress syndrome, as several studies have done since then.

The study also found that experiencing GI symptoms increased the risk of undergoing procedures with major health risks, such as non-invasive mechanical ventilation and tracheal intubation.

And an October 2020 report found that children with COVID-19 who develop GI symptoms are more likely to experience serious, critical infections and heart failure.

Another study from late January 2021 concluded that experiencing these symptoms also appears to increase the likelihood of serious illness and death in adults. An even more recent review found that people with COVID-19 and gastrointestinal symptoms when admitted to the hospital are also more likely to develop acute heart and kidney damage or die from the disease.

Dozens of studies have also found that people with previous GI tract conditions are more likely to experience serious illnesses and negative complications.

Research published this month found that people with gastrointestinal conditions, such as Barrett’s esophagus, are at increased risk of developing severe COVID-19 symptoms and diseases.

Some researchers speculate that this connection probably exists because gastrointestinal diseases can cause intestinal metaplasia, replacing the stomach wall with cells similar to intestinal tract.

Many GI conditions can also make it easier to develop GI infections because they damage the intestinal or stomach wall. Some of these conditions, such as irritable bowel syndrome, also cause over-expression of ACE-2, giving viruses more opportunities to enter cells.

Medications used to treat gastrointestinal diseases or symptoms can also lower stomach acid levels, making it easier to get the virus through food or other ingested substances. Normally, the high acid levels of the stomach are strong enough to deactivate viral particles.

There is less speculation as to why experiencing GI symptoms with COVID-19 increases the risk of serious illness and poor outcomes in the absence of underlying conditions.

People with viral infections in their respiratory and intestinal tract are exposed to increased viral load compared to people with infections in only the respiratory tract.

There are also about 100 times more ACE-2 receptors in the GIT than respiratory organs, so it can house more viruses if it gets infected.

People with symptoms that affect multiple organs also tend to experience worse diseases and poorer outcomes.

Early evidence seems consistent. But on a broader scale, long-term studies should determine the true link between GI symptoms, GI conditions, and COVID-19.

For example, some research suggests that people who develop GI symptoms with COVID-19 may experience milder illness.

Knowing how often, when and why COVID-19 causes GI symptoms can have significant benefits.

If these symptoms are as common as research shows, doctors and nurses can start testing people with these indicators, namely loss of smell and taste, fever, anorexia and diarrhea, which are very specific to COVID-19 infection – even in people without respiratory symptoms. This may help identify potentially millions of COVID-19 cases earlier, including otherwise asymptomatic cases.

Tracking GI symptoms in a population can also help identify disease outbreaks before they occur.

In a study comparing the number of Internet searches for these symptoms commonly associated with COVID-19 in 15 countries, it was found, in some countries, increases in searches occurred 3-4 weeks before increases in case levels.

Researchers also need to know if GI diseases that already exist increase the risk of getting serious illnesses, negative complications and death. They will also need to find out if gastrointestinal conditions make someone more susceptible or susceptible to the development of COVID-19. It can teach healthcare professionals how to better handle potential, active or resolved cases of COVID-19 in people with gastrointestinal diseases.

It is also important to learn whether COVID-19 can spread through feces and how long someone stays contagious.

In a review in early February, 26.7% of fecal samples from individuals with confirmed COVID-19 viral RNA contained and shed contaminating particles for approximately 19 days.

If the disease can spread through feces, it can change current hygiene and self-isolation recommendations.

The Centers for Disease Control and Prevention (CDC) currently also only recommends that people isolate themselves 10-20 days after the onset of symptoms. If someone’s feces can spread infection longer, public health agencies should consider reviewing their guidelines.

If feces containing the new coronavirus can spread the infection, it is also important to monitor and possibly treat wastewater to reduce transmission. The CDC already has the tools to help states create their own sampling strategies for monitoring.

Researchers also need to know more about the long-term GI impact associated with COVID-19.

Some preliminary studies show that certain symptoms may persist for weeks to months after recovery from the disease. A recent survey found that about 16% of people may still experience nausea and vomiting after recovering, while 12% may experience digestive disorders.

It will take time to really discover when and why COVID-19 causes GI symptoms, and how it affects the severity and outcome of diseases. And it will probably take much longer to figure out if and how often, symptoms become long-term.

But scary as it may sound, this knowledge can bring about significant improvements in the way we diagnose, treat, monitor, and detect COVID-19.

For live updates on the latest developments regarding the new coronavirus and COVID-19, click here.