WASHINGTON - Carbon monoxide can be fatal, and sometimes difficult to detect.

According to data by the Centers for Disease Control and Prevention, January is the worst month of the year for carbon monoxide poisoning.

Unintentional carbon monoxide exposure accounted for 15,000 emergency room visits annually between 1999 and 2004 with an average of 439 people dying each year.

Kanta Sircar, an epidemiologist with the CDC, says this is the time of year when risk factors are at their highest.

"In the winters, we have seen more cases of carbon monoxide poisoning than any other time of the year - one, because of when the weather gets low, we use our furnace and heating systems more," she explains. "Furnaces, if they are not properly maintained, can emit carbon monoxide poisoning. "

While carbon monoxide is odorless, it is sometimes associated with the smell of natural gas. The CDC recommends you seek prompt medical attention if you feel dizzy, light-headed or nauseated and suspect it to be CO poisoning.

Sircar says there are a number of ways to protect yourself from what some dub the silent killer, including avoiding heating your house with a gas oven and never running a car or truck inside a garage attached to your house, even if you leave the door open.

Sircar highly recommends updating or purchasing a carbon monoxide detector.

"First and foremost, install a battery-operated or battery-backup CO detector in the home," she says. "Or, if you have one already, the battery-operated, you know, replace the battery. Usually, you want to do that in spring or fall, when you change your clock, but this is a great time to do it."

Sircar says the most common symptoms of CO poisoning are headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion.

If you experience any of those common symptoms, she says to immediately leave the residence and call 911.