I applaud this very nice essay in ACSH output for today on how to distinguish the flu–caused by influenza virus, from colds caused by any number of viruses.
Flu is a much more serious and debillitating illness than a cold and we always distinguish it by presence of a fever.
People with flu say they feel they’ve been hit by a truck they are not having a cold.
Influenza viral pneumonia and pneumonia after Influenza are bad news, particularly problematic in children, older and pregnant patients, serious, and produce the deaths from flu epidemics. The Swine Flu epidemic after WWI around the world probably kill more than 25 million.
The big thing is fever and severity of systemic symptoms. Here’s the ACSH essay.
There are a few other viruses like Respiratory Syncytial Virus (RSV) that cause illness that is worse than a cold, in the case of RSV Bronchiolitis, that looks like asthma. I have seen epidemics of RSV that impacted adults–not a happy thing–looks like an epidemic of asthma. Croup with the stridorous breathing and barking cough is caused by para influenza virus, adenoviruses and sometimes RSV, sounds scary, easy to treat usually and short-lived, no fever. A croupy cough with fever could be a troublesome tracheal infection so high fever with croupy cough is not benign and should be seen by a doc.
Colds are caused by all kinds of viruses, rhino, adeno. most be distinguished from allergic rhinitis with cough or it doesn’t go away. Same is true of cough related to asthma–such as nightime cough–winter does produce some allergens, outside and inside.