COVID-19 and flu have very similar symptoms. Winter season in the northern hemisphere is a flu season. At the same time, we now have COVID-19 pandemic going on. Clinical features of flu have been well studied over the last few decades. COVID-19 clinical features are becoming more evident in the recent past as more and more people got affected.
Clinically, it is not easy to differentiate COVID-19 from flu. Both these conditions are caused by respiratory viruses with similar presentations. Modes of transmission, clinical features, and complications are similar. There are subtle differences between these two diseases. Flu is more common in children and young adults more than COVID-19. The time between exposure to infection and developing symptoms (incubation period) is about 1-4 days for flu and 2-14 days for COVID-19. While fever and cough are common in both COVID-19 and flu, sore throat is more common in flu than COVID-19. Redness in the back of the throat (pharyngeal erythema) is the most common sign found in people affected with flu. Sore throat occurs in only 14% of the COVID-19 affected people. Runny nose and nasal congestion are seen only in 5% of the patients with COVID-19 illness. These symptoms are seen more often with flu. Gastrointestinal symptoms like nausea, vomiting, diarrhea and abdominal pain are seen in around 4-10% of the COVID-19 affected people. These symptoms are usually not seen in individuals affected by flu. Even though laboratory findings like low lymphocyte count and low platelet count are seen with flu, these findings are more often with COVID-19.
The differences in the clinical features between COVID-19 and flu are so subtle that it is not easy to differentiate between these two conditions. Besides, both these conditions can coexist making things more complicated. The best way to differentiate is to do flu test and COVID-19 test. RT-PCR test used to detect these viruses is probably the best approach to diagnose flu versus COVID-19. Flu has an effective antiviral drug which may help to reduce the severity and the duration of the illness, whereas COVID-19 treatment options are still evolving.
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