When the morning starts with enough symptoms for a cold-remedy commercial - cough, sneezing, headache, muscle aches, fever - the big decision is whether you should go to work or call in sick.

Most people who get a cold bundle up and go to work. But doctors say that's not always the best thing to do. Sometimes it's best to stay home and get some rest in the name of personal and public health.

"You stay home because you feel bad and you want to get better faster," said Justin Spring, author of "The Little Cold Book: Advice, Remedies & Bedside Amusements" (Quirk Books, 128 pages, $9.95). "But in terms of being polite . . . it's all about courtesy. There's also the question about how tough is your boss going to come down on you if you miss a day's work."

He said he thinks most bosses "feel that if you're really sick, and you're coughing and sneezing and releasing all sorts of viruses, (you) actually do the organization a better turn by staying home than going into the office."

If you do stay home, you're not alone. Federal agencies reported that in 2001, about 75 million workdays and 22 million school days were lost due to colds and flu.

So, when are you contagious enough to stay home? How do you tell if your cold is something more insidious? Often, the bad stuff - influenza, upper-respiratory infections, bronchitis and even meningitis and pneumonia - starts life resembling a cold.

In the best-case scenario, staying home actually helps you heal faster, said Dr. Mark Mengel, professor of family practice at St. Louis University School of Medicine. "You're putting all your energy into fighting the cold," he said. "The benefit is you don't spread it around."

Still, "It's a difficult question," said Dr. Janak Koirala, assistant professor of infectious disease at Southern Illinois University School of Medicine in Springfield. "On one hand, you don't want to miss work, or stay away from school and miss classes. On the other hand, you want to think about the health of the public."

Doctors have an informal hierarchy of symptoms that signal it's time to stay home. Most of all, if you feel miserable, as opposed to somewhat uncomfortable, stay home.Mengel said people often don't take cold symptoms seriously. Most respiratory illnesses start with cold symptoms, but they worsen steadily, sometimes rapidly. If you suspect that you have a contagious disease worse than a cold, don't go to work. "If you feel so rotten that you won't be able to focus on work, stay home and rest, because you'll wind up having to re-do what you messed up anyway," Mengel says."A sore throat, stuffy nose, cough and sneezing can be symptoms of both a cold and the flu," he added. "However, if you have the flu, you feel a lot worse and are likely to have other symptoms, such as a high fever that lasts three to four days, a headache, muscle aches, exhaustion and weakness."

Other red flags can signal your bug is worse than a cold.Fever is the king. It's the one symptom that signals you might want to stay in bed and eat chicken soup. Contagious illnesses more serious than colds tend to cause higher fevers. Doctors say that in general, fevers due to colds peak at 102 degrees.Public enemy No. 2 is a headache. Pair a fever and a headache and you're headed for a rough week.Other symptoms that signal worse-than-a-cold illnesses are: muscle aches, joint aches, fatigue, dizziness, rash, vomiting and diarrhea.Coughs that get worse can signal bronchitis. Meningitis starts with flu symptoms. Pneumonia starts out seeming like bronchitis.

Shool systems generally have the same recommendations - which seem based on common sense - for parents. They are: a temperature of 100 degrees or higher and/or any of these symptoms: nausea, diarrhea, vomiting, sore throat, lack of energy, bad coloring and headaches.Richelle Clark, director of health services for St. Louis Public Schools, said students should not return until they're symptom-free for 24 hours without the use of medication.

This time of year, the big question is whether you've caught influenza. The shortage of flu vaccine this year adds another level of tension.Once the flu takes hold, it's no longer a decision of whether to go to work. You don't go because you can't.The best way to fight the flu is to avoid it, doctors say. Along with frequent handwashing and avoiding touching your eyes, nose and mouth, caution starts with reading the news."Influenza epidemics always start in the schools," said Dr. Michael Cooperstock, professor of pediatric infectious diseases at the University of Missouri School of Medicine in Columbia.Once schools report rising absentee rates - especially when those rates approach 15 percent - the rest of the community won't be far behind, Cooperstock said. At that point doctors see increased emergency-room and office visits.For some people, especially older individuals and those with compromised immune systems, the flu can be fatal. Cooperstock recommends they seek out the vaccine. The shots are still available; your doctor or local health department should know where to get them."We started out thinking there was going to be a shortage, but now we have vaccine still available; that means all of the people who are at risk haven't been vaccinated," Cooperstock said.While Cooperstock's hospital has not seen an ominous rise in flu infections, the heaviest part of the season occurs from January through March. As of early January, area doctors hadn't reported an unusual rise in cases of flu.

If you do decide to go to work and you later find out you're carrying more germs than you thought, don't feel guilty if your co-workers end up sniffling, doctors say. There's no way to tell where anyone got a germ. In an interactive society, germs regularly use people for mass transportation-children especially."People's lives are so complicated, no one is completely isolated from other people," said Cooperstock. "Even kids who stay home have siblings in school and parents who go to work."People get infections from countertops, friends, doorknobs, desks, grocery carts, other people's hands - anywhere people touch each other or touch things other people have handled. And there are lots of germs to pass around."There are 300 different viruses that can cause upper-respiratory infections," said Cooperstock.They're in the environment year-round, although infections are more prevalent in winter.

Most contamination comes from touching contaminated surfaces, the most common being hands. People sneeze and cough into their hands, then touch other things - including people.Because of that, the Centers for Disease Control and Prevention has coined a new term, "respiratory hygiene," Cooperstock said.It could just as well be called respiratory courtesy. Here are some measures you can take to reduce the spread of germs:If you don't have tissue, cough or sneeze into the bend of your elbow, not into your hands. This keeps the hands from carrying germs around the office, home or school.Remember that a sneeze or cough has range of about three feet. If you're going to sneeze or cough, try to back up and cover your mouth and nose.Wash your hands frequently for about 20 seconds with soap and water. Most infections are spread through the hands. Touch a contaminated surface and then touch an entry to your insides - scratch your nose or eye, or lick your finger - and you're going to get a bug.If washing isn't an immediate option, invest in hand sanitizer. The alcohol actually works better than soap for killing germs, and the sanitizer contains emollients that protect the skin.