DENVER -- This fall offers a cornucopia of viruses, everything from the H1N1 flu to the common cold.

It can be difficult to tell if those sniffles are something to be concerned about.

"Colds and other illnesses we see this time of year are also caused by viruses, so there is some overlap in symptoms, but there are some very big differences," said Dr. Dianne McCallister, chief medical officer at Porter Adventist Hospital.

In general, the flu causes high fevers (over 101 degrees fahrenheit), severe aching in the muscles, dry cough and a great deal of fatigue.

H1N1 also has some gastrointestinal symptoms.

Fever usually does not accompany colds. People usually experience mild achiness, runny nose, scratchy throat and feeling run-down -- but able to function.

"Most healthy adults and children will recover with acetaminophen to treat the aches, lots of liquids, rest and TLC. However, there are a group of people that the CDC is recommending get antiviral medication right away for their flu," said McCallister.

Those include children younger than 2 years old, adults over 65 years old, pregnant women, persons of any age with certain chronic medical problems and people with immunosuppressive disorders or medications.

"Children and teenagers should not receive aspirin while sick -- it can lead to a dangerous side effect called Reyes syndrome that damages the heart," said McCallister.

If any of the following symptoms occur, you should get immediate medical attention:

difficulty breathing or chest pain

fever lasting more than three days

purple or blue discoloration of the lips

vomiting and inability to keep liquids down

signs of dehydration, such as feeling dizzy when standing or being unable to urinate

confusion or increasing lethargy (sluggishness)

flu-like symptoms improve but then return with fever and a worse cough

For information about seasonal or 2009 H1N1 influenza, call CoHELP at 1-877-462-2911 or visit the CDPHE Web site at www.colorado.gov/nofluforyou.

Red Cross flu information: www.redcross.org/pandemicflu.

Visit McCallister's blog at blog.porterhospital.orgfor more information.