Q: If you are feeling sick, is there a way to determine if you have a bacterial versus viral infection without going to the clinic? For example, temperature? Swollen glands? Green snot? Coughing up stuff?

A: The short answer is no. There is no sure-fire way to tell without going to the clinic. However, if I were a betting woman, I’d put money on a virus, and I’d win big. Viruses cause the vast majority of respiratory infections. That includes most colds, sinus infections, bronchitis and most ear and eye infections. It includes most cases of fever, swollen glands, green snot and coughing up stuff.

Viruses and bacteria are two kinds of infectious organisms. The practical difference between them comes in with the question of antibiotics. Antibiotics kill bacteria. Antibiotics do not kill viruses. Your body does kill viruses, for free. No clinic charge, no waiting in lines, no pharmacy charge. All it needs is some rest and time.

Now, everyone has a story of going to the doctor for a respiratory infection and leaving with a prescription for antibiotics. We hear it all the time. “Last time I had the same symptoms, and I got antibiotics and it cleared right up.” Naturally, the patient wants the same treatment this time. The truth is she probably would have gotten better anyway. The timing of the antibiotics with her improvement convinced her that the antibiotics were responsible for her recovery.

Since you brought up the color of your secretions, allow me a brief digression on the subject. Mucous color is a commonly misused criterion for when to see the doctor, or when to expect antibiotics. Your nasal passageways normally produce clear mucous.

This helps moisturize the tissues and wash out debris and germs.

When you get sick, your immune system responds by sending in white blood cells. This adds a yellow color to the mucous. At the same time, the amount of mucous produced goes up as your body rids itself of the infection. When that happens, the bacteria that normally live in your nose get very happy, because mucous supports them. They multiply, and this turns everything green.

So yes, technically, green snot means bacteria are present, but usually they are just squatters taking advantage of the situation and not the cause of the problem at all. Taking an antibiotic can change the mucous color back to yellow but that does not mean it cured the underlying problem, which is a virus infection.

Unfortunately, sometimes doctors prescribe antibiotics when they aren’t needed, “just in case.” This causes a couple of problems. For one, it sets up a patient like the one above to expect antibiotics for viral infections. That creates busy clinics and dependent patients, who think they can’t get over a simple cold without professional help.

On a wider scale, when we carpet bomb bacteria with antibiotics, most bacteria will get killed. But a few will develop resistance to the antibiotic, and survive. The survivors can multiply and create a whole new group of tougher germs. Now science has to create a stronger antibiotic to kill these super-bugs. There have been some very scary germs created by this exact scenario.

I trust I’ve made my point about viruses. But remember, I said most respiratory infections are caused by viruses. That means some are caused by bacteria. For example, the bacterium Streptococcus pyogenes causes a throat infection commonly called strep throat.

That definitely requires an antibiotic, to kill the bacteria and prevent dangerous consequences of the infection. Most kinds of pneumonia require an antibiotic, as do some ear and eye infections and, rarely, sinus infections.

If you’re looking for criteria, I suggest the following. If you get a respiratory infection, with the usual sore throat, congestion and cough, give your body a few days to work on it.

Take over the counter remedies if you like. Drink lots of liquids to keep the mucous flowing. Try a sinus rinse.

But if you have a high fever, a really bad sore throat that lasts for more than a few days, trouble breathing, or symptoms that last longer than a week, come in to the clinic for evaluation. Err on the side of caution, and come in to SHAC if you have doubts. Call 277-3136 for advice or for an appointment.

Dr. Peggy Spencer is a physician at Student Health and Counseling. She is also co-author of the book “50 Ways to Leave Your 40s.” Email your questions directly to her at pspencer@unm.edu. All questions will be considered, and all questioners will remain anonymous.