Judy Skeie-Voss doesn’t know what kind of sick bug has been bugging her for so long, but whatever it is, she’s tired of it.

“I’ve been sick since Black Friday,” she said. “It’s lasting forever.”

Piles of tissue testify to her symptoms: constant runny nose, coughing and hacking up phlegm from deep inside her chest. Right now, she’s surviving on cough drops and liquids.

“I really don’t think there is anything I can take. It’s just going to have to run its course,” said Skeie-Voss, 52, who suspects a virus is to blame for her misery.

If it was a bacterial bug, she reasoned, she’d feel a whole lot worse. She’s giving it one more week to clear out before heading to the doctor.

Pinpointing the culprit behind your winter crud — virus or bacteria — is the first step in understanding how to treat it. At a time when public health officials warn that antibiotics are overused, getting the right diagnosis takes on new significance. Antibiotics work on bacterial infections but not on viruses.

“It boils down to that one decision: Are you going to treat with antibiotics or not?” explained Dr. Frank Rhame, a physician specializing in infectious disease at Allina Health Uptown Clinic in Minneapolis. “It’s not always easy. You don’t want to miss a bacterial infection, and you don’t want to overtreat a viral infection. But we’re helped by the fact that they’re usually viral.”

Even doctors have trouble nailing down the sick bug. With no surefire test to find out if it’s a bacteria or a virus that’s attacking your body, they rely on symptoms to make a diagnosis.

“We spend a lot of time thinking about it, and we agonize a lot about it,” he said.

A matter of time

Symptoms for viral and bacterial infections are often very similar in the early stages of an illness. Mucus, sneezing, congestion, cough and sometimes even a fever are common.

“The ones that are easy are the people who have mostly runny noses, a little sore throat, maybe a little cough. They’re in their first week of illness,” Rhame said. “They don’t have a fever. They don’t have chest pain. You don’t hear anything when you listen to their chest. You don’t feel swollen lymph nodes in their neck. You don’t see any pus in their throat. Their ears are not red. You know that person has just got a cold. Those are the easy ones. And most people are like that.”

Up to 15 different viruses can cause the “common cold,” he said. But the real world does not always present such clear-cut cases.

If the person has a fever or their cough is especially bad, doctors worry more. If they have a ferocious sore throat or a painful headache, doctors wonder if it could be something serious.

“All of those things would point you away from a pure virus,” Rhame said. “If any of those things are present, it makes you worry that there’s a bacterial infection.”

Duke University researchers are working on a blood test that could issue a verdict on the viral vs. bacterial question with the same speed and accuracy of a pregnancy test. The tool works by taking a snapshot of what certain genes are doing. The researchers have learned that during a viral attack, some 30 genes react by defending the body from the invader. A different set of genes responds when it’s a bacterial infection. The test is still under development.

In the meantime, Rhame said, he will sometimes order a white blood cell count to help render a ruling.

During a bacterial infection, the body produces a particular type of white blood cell to counter — and that increases the total number of white blood cells.

Heating up

Still, one of the best clues to figuring out if a patient has a bacterial infection is simple: time. After about a week, most cold symptoms go away — except for the cough. That can last for two to three more weeks, Rhame said. He said he usually advises patients to call or come back if they’re not feeling better after a week’s time.

A high fever — greater than 101.5 degrees — is a strong indicator of a bacterial infection, said Dr. Peter Bornstein, an epidemiologist with Health­East. “It’s not always easy to tell,” he said. “This time of year we have a couple different viruses going around.”

The flu is caused by a virus, and Minnesota, like much of the rest of the country, is grappling with a flu epidemic. For that, Rhame and Bornstein said, a flu shot is still the best prevention. There are also anti-viral medications that can be prescribed. Telltale signs include: body aches, sore throat, fever and headache.

“If you’re not sure if you have it, then you probably don’t have it,” Bornstein said. “You feel like you’ve been hit by a truck.”

Skeie-Voss, of Woodbury, says her unnamed illness hasn’t knocked her off her feet. But it has slowed her down some, and its tenacious grip on her body is frustrating and perplexing.

“It’s just this nagging crud that won’t go away,” she said.