Fever, runny nose, sore throat, headache, fatigue -- just another run of the mill cold or flu virus, right?
Perhaps, but sometimes these rather nonspecific symptoms are harbingers of something else. A number of illnesses, particularly viral infections, can begin with symptoms that are similar to a cold or the flu but, upon closer inspection or further progression, can prove far more serious than a flu bug.
Part of the reason many infections can be mistaken for a cold or a flu is because their symptoms are fairly non-specific. And they like to infect similar areas of the body.
"Flu, until it lays you out in the bed ... it really doesn't have a completely distinct set of symptoms. There's a lot of overlap," said Dr. William Schaffner, chair of the Department of Preventive Medicine at Vanderbilt Medical School in Tennessee.
Many of these symptoms are respiratory in nature -- nose, throat, and breathing-related -- because those are the places where viruses invade the host and begin to infect, prompting the immune system to try and fight them of.
But there are a few things to look out for that can alert you to something unusual.
In general, the longer an illness lasts, the more serious it may be. This criteria is different for different age groups. Children, for example, tend to have about eight colds or flu viruses each year, lasting a few weeks. Adults, on the other hand, have about three of these infections each year and they might last about one week.
The time of year is a factor. Getting a cold or flu-like symptoms in the spring or summer months might be treated with more suspicion than in the winter months, when it is more likely that illness is the result of a virus that is going around.
Finally, changes in symptoms, such as a second fever, a new rash, or developing symptoms out of the blue are a major indication that something out of the ordinary is going on.
"You know your body better than anyone," said Dr. Erica Brownfield, associate professor of medicine at Emory University School of Medicine in Atlanta. "Not that you should go for those rare zebras right up front, common things are common, but if there is something that doesn't make sense or doesn't seem right ... it could be something else."
"Pneumonia can be very difficult to differentiate between the flu and the common cold," Brownfield said.
According to Dr. Owen Hendley, professor of pediatrics at the University of Virginia School of Medicine, a typical patient story may begin with complaints of a runny nose, a cold and a fever. After several days, a second fever and perhaps coughing up more phlegm could indicate pneumonia, an illness that can lead to difficulty breathing, pain, bouts of coughing and more acute fevers.
Pneumonia is secondary to the alteration of a host's defenses. That is, once a virus has already weakened a person's immune system, pneumonia is able to infect.
In addition, it may be wise to consider what time of year it is and if people around you are sick.
In the winter, doctors may see many flu patients, all with the same symptoms, Shaffner said.
"If the ER is full of flu patients, and it's flu season, the doctor is likely to say: If it walks like a duck, quacks like a duck, and looks like a duck, it's probably influenza."