Over two million people and counting have tested positive for coronavirus in the United States, according to the World Health Organization.
As Americans navigate the virus amid rising case numbers, health officials say it's important to know which symptoms to look out for.
In addition to more common symptoms specified by the CDC, health experts have seen the virus manifest in a number of rarer, odder and more unique ways.
Below are some lesser known symptoms to look out for.
According to U.S. News, several doctors found that rashes inside the mouth have been seen in some people with COVID-19. An American dermatologist looked into the study and found that the rashes are known as enanthem. "An enanthem is a rash [small spots] on the mucous membranes," Dr. Michele Green, who practices at Lenox Hill Hospital in New York City, said.
Green shared that it is very likely in patients with viral infections like chickenpox, and hand, foot, and mouth disease.
The new study was published on July 15 in JAMA Dermatology. Researchers looked at 21 patients diagnosed in early April with coronavirus. These patients also had skin rashes. Six patients (29%) had enanthem on the inside of their mouths. The affected patients ranged in age from 40 to 69.
Nausea, diarrhea and other digestive symptoms
Early in the outbreak of the virus, researchers reported that nearly half of COVID-19 patients complained of diarrhea and other digestive issues.
"Clinicians must bear in mind that digestive symptoms, such as diarrhea, may be a presenting feature of COVID-19, and that the index of suspicion may need to be raised earlier in these cases rather than waiting for respiratory symptoms to emerge," wrote investigators from the Wuhan Medical Treatment Expert Group for COVID-19.
According to findings, these patients with digestive symptoms exhibited various issues, including loss of appetite (nearly 84%), diarrhea (29%), vomiting (0.8%) and abdominal pain (0.4%).
The research also showed that patients with these symptoms waited longer to be admitted to the hospital — 9 days versus 7.3 days — suggesting they took longer to seek care because they didn't display more typical respiratory issues.
Pediatric multisystem inflammatory syndrome
A dangerous inflammation of the heart and other organs has been detected in child patients with COVID-19 across the country.
Just this week, doctors dubbed the symptoms with an official name: pediatric multisystem inflammatory syndrome.
Children exhibiting the rare but dangerous complication have been identified across the country, in at least seven states and the Washington, D.C. area, according to a May 7 report from NBC.
The outlet reports at least 85 such cases in children across the U.S., with the majority out of New York State.
The symptoms, which can inflame blood vessels in the heart, were first reported in late April.
Doctors say that the increased occurrences do not necessarily suggest that the number of cases has grown. Rather, they surmise that it is likely the result of an increased awareness of the strange symptoms.
The syndrome mirrors symptoms of other inflammatory illnesses, such as Kawasaki disease and toxic shock-like syndrome.
"All the kids have some sort of severe inflammation," said Dr. Michael Bell, head of critical care medicine at Children's National Hospital in Washington, D.C., where two cases have been reported, with 15 more children in intensive care displaying some kind of massive inflammatory response to COVID-19.
"I think it's all part of some spectrum of disease that's evolving as we learn more and more about this infection and its consequences,” Bell added.
The new syndrome seems to be the result of a children’s immune systems going into overdrive following a coronavirus infection, although it is too soon to pin all of the cases on the virus.
"We're all still waiting for the smoking gun to be sure it is associated with COVID-19," said Dr. Audrey John, chief of pediatric infectious diseases at Children's Hospital of Philadelphia.
However, the occurrences are "certainly suspicious," John added.
Doctors have been confounded by an odd new coronavirus symptom referred to by some as "happy hypoxia."
Also dubbed with the more neutral term "silent," the symptom is observed in some COVID-19 patients who are talking and in no discernible distress, yet exhibit oxygen levels low enough to cause unconsciousness or death, reports The Guardian.
While a person of normal health can be expected to have an oxygen saturation of 95% or more, doctors who have observed the strange effect have reported coronavirus patients with levels in the 80s, 70s and even 50s or lower in some extreme cases.
It's no wonder that this symptoms is raising serious questions about what physicians know about the virus's effects on the lungs, and whether there could be more effective ways of treating it.
“It’s intriguing to see so many people coming in, quite how hypoxic they are,” said Dr Jonathan Bannard-Smith, a critical care and anaesthesia consultant at Manchester Royal Infirmary in the UK.
He added: “We’re seeing oxygen saturations that are very low and they’re unaware of that. We wouldn’t usually see this phenomenon in influenza or community-acquired pneumonia. It’s very much more profound and an example of very abnormal physiology going on before our eyes.”
Dr. Mike Charlesworth, an anaesthetist at Wythenshawe hospital in Manchester, said that low oxygen levels caused by lung conditions that manifest as hypoxia typically leave patients feeling significantly ill. But this is not necessarily the case with individuals who suffer this strange COVID symptom.
“With pneumonia or a pulmonary embolism they wouldn’t be sat up in bed talking to you,” Charlesworth said. “We just don’t understand it. We don’t know if it’s causing organ damage that we’re not able to detect. We don’t understand if the body’s compensating.”
In fact, Charlesworth lived through the symptom when he was suffering from the virus himself back in March. Sick, with a fever and cough, the doctor spent 48 bed-ridden hours exhibits signs of hypoxia.
“I was sending very strange messages on my phone. I was essentially delirious," he said. "Looking back I probably should’ve come into hospital. I’m pretty sure my oxygen levels were low. My wife commented that my lips were very dusky. But I was probably hypoxic and my brain probably wasn’t working very well.”
Conventional medical wisdom states that as oxygen levels in the body decrease, vital organs like the heart and brain are at risk, with patients typically losing consciousness at sub-75% level saturation.
In such cases, the body is left feeling breathless as higher levels of carbon dioxide make it harder for the lungs to clear oxygen. But in the cases of "happy hypoxia" seen in coronavirus patients, this vital response does not kick in.
One strange side effect of coronavirus could be foot sores, according to a team of Spanish physicians.
The Spanish General Council of Official Podiatrist Colleges has warned experts that some patients have experienced lesions on their feet, the New York Post reports.
The researchers say that the marks are "similar to chickenpox or measles."
“They are purple lesions (very similar to those of chickenpox, measles or chilblains) which usually appear on the toes and normally heal without leaving a mark,” the organization stated.
While the so-called "COVID toe" symptoms have mainly appeared in children and adolescent with COVID-19, it has also been detected in some adult patients.
The council clarified that despite reports, there have been no scientific studies to back up the findings.
Some COVID-19 patients have warned of a peculiar symptom referred to as "fizzing."
The side effect — a buzzing sensation felt throughout the body — has been reported by patients describing symptoms on Twitter.
One user, @miafia, described the "electric feeling on my skin" that she felt from her first day of COVID-19 symptoms.
While doctors who have treated virus patients say it's not common, they surmise it may be an autoimmune response that effects patients’ nervous system.
Dr. Daniel Griffin, who estimates that he’s seen about 50 coronavirus patients daily since the illness gripped New York, says he’s heard mention of the reaction.
“Clearly it’s been identified, but we’re just not sure yet how widespread it is,” Griffin, who is chief of infectious disease at ProHealth Care Associates, told New York Post.
Griffin ponders whether the feeling may result from disease-fighting “antibodies interfering with the way nerves work,” but says neurologists still aren’t sure if it’s the body’s response to the virus or the virus itself causing the feeling.
Loss of smell
“Significant numbers” of known coronavirus patients with lost or reduced sense of smell have been reported by South Korea, Italy and China, according to USA Today.
In a joint statement, Claire Hopkins, president of the British Rhinological Society, and Nirmal Kumar, president of ENT UK, wrote about the occurrence of anosmia (the loss of smell) in patients around the world, including those who otherwise don’t exhibit major symptoms.
"In Germany it is reported that more than 2 in 3 confirmed cases have anosmia,” they wrote. “In South Korea, where testing has been more widespread, 30% of patients testing positive have had anosmia as their major presenting symptom in otherwise mild cases.”
Loss of taste
In addition to loss of smell, COVID-19 patients have reported loss of taste.
NBA player Rudy Gobert of the Utah Jazz revealed he experienced both loss of taste and smell after testing positive for the virus in March.
“Just to give you guys an update, loss of smell and taste is definitely one of the symptoms, haven’t been able to smell anything for the last 4 days. Anyone experiencing the same thing?” Gobert tweeted.
While both loss of taste and smell can be symptomatic of the seasonal flu, they strike a very specific demographic of coronavirus victims, according to Dr. Gregory Levitin, an otolaryngologist at New York Eye and Ear Infirmary of Mount Sinai.
"What is most unusual about this new finding is that the loss of smell or taste was the only presenting symptom in a group of patients under the age of 40 who ultimately tested positive for the COVID-19 virus," Levitin wrote in an email to USA TODAY.
This week it was revealed that coronavirus can spread to the eyes.
On March 24, the American Academy of Ophthalmology shared an alert warning that COVID-19 may cause conjunctivitis, or pink eye, in about 1-3% of infected people, reported TODAY.
Pink eye is inflammation of the clear tissue covering the white part of the eye.
While virus particles have been found in eye secretions, the AAO suggested that the risk of being infected with the virus via tears is low.
The Life Care Center in Kirkland, Washington has been described as “ground zero for the West Coast's coronavirus outbreak.” In an interview with CNN, one nurse from the center described the symptom in her patients.
“They have, like ... allergy eyes,” the nurse said. “The white part of the eye is not red. It's more like they have red eye shadow on the outside of their eyes.”