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How Can I Tell If My Infection Is From a Virus or Bacteria?

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Updated November 21, 2011

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Question: How Can I Tell If My Infection Is From a Virus or Bacteria?
As you may know, bacterial infections can be treated with antibiotics. However, antibiotics are often overused and authorities now caution against using them for things like viral infections, which aren't affected by antibiotics. So, how can you tell the difference?
Answer: You can't. At least, you can't without help from a doctor.

You may be tempted to try diagnosing your own infection at home without seeing the doc, either because you want to save money or time. You might figure if it's a viral infection and you can't get any help from antibiotics, what's the reason for going to the doctor?

I'm not suggesting everyone with a common cold needs to go running to the doctor, but there are a couple of problems with making your decision based whether or not you think it's a viral infection or not.

  1. Depending on the type of viral infection, there may still be medications that can help. The meds specifically targeting viruses are called antivirals. They're not used as often as antibiotics, but in some cases they help a lot.

  2. There's absolutely no way to tell if an infection is caused by bacteria without a test. There are some telltale signs that help point us in the right direction, but unless it's life-threatening, most docs will take a sample before doling out antibiotics. The sample taken depends on the suspected infection, and can include a blood sample, throat culture, skin swab, or more.

I understand the desire to diagnose at home, but rather than wondering if the infection is viral or bacterial, instead focus on whether you need to see a doctor.

Here are some good rules of thumb when trying to decide whether to see the doc. Make an appointment if you see any of the following:

  • Dehydration. Mom always wants to bring you chicken soup when you're sick. The doctor always tells you to drink clear fluids (chicken broth counts). Staying hydrated helps you thin out the mucus your body is producing. While your immune system fights infection -- of either type -- it uses mucus to carry away the virus or bacteria from the body. If the mucus is too thick, say from dehydration, the infection could get worse. Indeed, bacteria can take hold in mucus that was originally produced while your body was fighting a virus.
  • Shortness of breath. If an infection is attacking your lungs or airways, it's time to see the doc. Pneumonia or asthma with bronchitis can become life-threatening if not treated promptly and appropriately.
  • Weakness, confusion or fainting. Combined with the usual suspects of fever, chills and body aches, any version of fatigue or weakness is a sign of serious infection.
  • Suddenly getting worse. If you're plugging along, especially if it feels like you might be beating this thing, and suddenly you feel worse, it's probably time to see the doctor. Sometimes one infection opens the door to another. Like I said already, mucus produced by viral infections can sometimes be a great place for bacteria to grow.
  • Kids with fevers. Fevers are a common part of viral illnesses in children -- most of which improve with supportive care (fluid, medicine to bring down the fever, and perhaps a big dose of TLC). Talk to your doctor about situations that might require a visit to the doctor.

You may have heard that green mucus or a wet cough is a sign of a bacterial infection. It might be true that green snot is a sign that something is growing in there, but it doesn't exclude the possibility that something else caused the infection in the first place. Either way, base your decision of whether to go to the doctor or not on how you feel.

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