Last week the number of confirmed cases of the coronavirus passed the 1 million milestone, and it continues to grow at an alarming rate. However, not all of these infections have presented themselves in the same way. Coronavirus patients are showing a wide range of symptoms and the exact reason why is still a mystery — but we do have some clues as to what factors can influence the severity of the disease.
While the most common symptoms are fever, cough and shortness of breath, there are numerous reports of coronavirus patients experiencing nonrespiratory symptoms. A study of 204 patients in Huabie, China, published in the American Journal of Gastroenterology found that just over half of patients experienced gastrointestinal symptoms such as loss of appetite, nausea, vomiting and diarrhea. The New York Times reports that the coronavirus sometimes presents with neurological indications, including swelling of the brain and seizures. Other cases have shown cardiac issues as well as muscle aches and extreme fatigue.
And then there are patients who have tested positive for the virus but report mild symptoms or none at all.
So why does the coronavirus affect people in such different ways?
“The basic premise is that humans are not machines,” says Yahoo News public health contributor Kathryn Jacobsen. “There are many factors that influence how our bodies react to pathogens. For coronavirus, two of the most important seem to be age and health status.”
The effect of age on the severity of coronavirus symptoms is relatively straightforward. “The way our bodies react to infections changes with age,” says Jacobsen. “People of any age can get sick from coronavirus and die from it, but the coronavirus fatality rate is highest in older populations.”
Those with comorbidities — two or more health problems at the same time — are also more susceptible to experiencing additional symptoms. “People with heart or lung disorders, diabetes, or other health problems may get sicker from coronavirus because of those underlying health issues,” says Jacobsen. However, the mechanism that links specific health issues and secondary symptoms has yet to be established.
Another possible factor in what symptoms a coronavirus infection presents is the level of exposure. “As with any other poison, viruses are usually deadlier in larger amounts,” wrote Drs. Joshua D. Rabinowitz and Caroline R. Bartman in an opinion piece for the New York Times.
“Stepping into an office building that once had someone with the coronavirus in it is not as dangerous as sitting next to that infected person for an hour-long train commute,” the two, who do research in genomics, said. “Low-dose infections can even engender immunity, protecting against high-dose exposures in the future.”
For the coronavirus, it is still too early to know exactly what else might influence how the infection presents in a particular individual, but it is likely to be a combination of factors. According to Jacobsen, tobacco use, nutritional status at both the macronutrient level and micronutrient level, medications, individual body chemistry, and genetics are among the many possible factors to consider.
Individuals known to have higher than typical risk of hospitalization if they contract the coronavirus have been advised to take extra care to reduce their risk of exposure to the virus. “That does not mean that people who are not in a high-risk group do not need to protect themselves,” says Jacobsen. “Low risk does not mean no risk.”
“Because it is impossible to know with certainty who will have mild symptoms if they become infected with coronavirus and who will develop severe or fatal disease, the safest option is for everyone to follow national, state and local guidelines for coronavirus prevention.”