When viruses collide: Flu season during pandemic


Risks of coinfection

About one in four COVID-19 patients have been diagnosed with an additional respiratory infection, including influenza (JAMA. 2020:323:2085-6). Pulmonologists must keep that in mind when managing COVID-19 suspects, said Dr. Singer.

“While it is true that most of the time COVID-19 travels alone, we have numerous examples in the literature and in our own experience that COVID-19 is accompanied by either another virus or another bacterial infection, including influenza,” Dr. Singer said. “The distinction is important. One is just for diagnostic reasons and public reporting reasons, but also because flu and COVID-19 have different requirements for how you care for patients in terms of the health system.”

Dr. Megan Conroy

Dr. Megan Conroy

Clinical suspicion for coinfection should remain high if the community spread of both COVID-19 and influenza is high, said Megan Conroy, MD, chief pulmonary and critical care fellow at Ohio State University, Columbus. “As the coronavirus first took hold in the United States in March 2020, we were at the tail end of influenza season, so it’s hard to predict what the upcoming influenza season will really look like with regards to coinfection.”

Distinguishing COVID-19 from flu

Multiple signs and symptoms between COVID-19 and the flu overlap. They include fever, chills, headache, myalgia, cough, and fatigue. Nasal congestion and sore throat are characteristic of the flu; shortness of breath and loss of the sense of smell have been widely reported in COVID-19. “While many upper respiratory infections can result in loss of smell, this may be more prevalent in COVID-19,” Dr. Conroy said. Other symptoms unique to COVID-19 are GI symptoms such as diarrhea and skin rashes such as acral ischemia.

Testing, however, is the cornerstone of the differential diagnosis. “You can’t confidently distinguish between them on symptoms alone,” Dr. Conroy added.

“I think the challenge we’ll face as clinicians, is caring for people with nonspecific symptoms of a respiratory viral illness, especially in the early phase of the illness,” said Dr. Solomon.

But even after that, symptoms can be difficult to distinguish.

“Later in the illness, COVID is more associated with a hypercoagulable state,” he said. “It is more associated with viral pneumonia on chest imaging, like the diffuse ground-glass infiltrates that we’ve all gotten used to seeing – but flu can do both of those things as well. So, without a test, it’s impossible to distinguish between the two infections in the clinic.”

But testing can have its shortcomings when flu season clashes with the COVID-19 pandemic. “Getting the test is not the same as getting the test results,” Dr. Solomon added. “Though a lot of people can get a test, if it takes 7 or 8 days to get the test result back, the result is useless.”

Widespread, rapid testing also depends on having adequate supplies of viral media transport and swabs. “I think that this is what we should be focusing on now: scaling up access to rapid turnaround testing,” he said. Distinguishing between the two is also important to preserve hospital resources. COVID-19 has more rigorous standards than flu for personal protective equipment and isolation of patients within the hospital.

Having chronic lung disease isn’t necessarily a risk factor for contracting COVID-19 or the flu, or both, Dr. Solomon said. “It’s a risk factor for having severe disease.” Again, he noted that flu vaccines are still necessary in these patients, as well as patients of advanced age and underlying medical conditions such as heart disease, diabetes, and obesity.

In managing children, it’s important to keep in mind that they communicate differently about their illnesses than adults, said Dr. Kaplan. “They may not have the words to tell you the same kind of thing that the adult tells you.” That’s where family members can help to flesh out the history. “They may present with an initially much milder form, if you will, where they’re not as critical up front, but then that small proportion of them comes back with the multi-inflammatory syndrome and then they are profoundly ill.”

Younger people make up a larger share of COVID-19 patients now, compared with the initial wave that hit the Northeast in the spring, Dr. Kaplan said. “We don’t know if that’s because the virus is a little different or the people that are getting sick are a little bit different.”

The COVID-19 strain now emerging may be less virulent than the strain that hit in early spring, he said. “That doesn’t mean that there aren’t still profoundly critical ill people with COVID of many different age ranges, that is true, but there are a lot of people that we now see will test positive, but aren’t really as profoundly ill as when it first landed here in the United States.”

That may be somewhat welcome as flu season arrives.

The physicians interviewed have no relevant disclosures.


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