User Reviewed

How to Tell a Viral from a Bacterial Infection

Three Methods:Recognizing a Viral InfectionRecognizing a Bacterial InfectionSeeking Medical Care

Everyone has gone through it—one day you are going along doing your routine, when all of a sudden you start to get a hint that you might be sick. Over the next 24 hours you develop a fever, runny nose, or sore throat (and sometimes all three). The question remains—what is making you feel so sick? Chances are it is either a viral infection (like the common cold) which will go away on its own, but it is also possibly a bacterial infection (like strep throat), which will require prescription medicine to treat. To learn how to differentiate between a viral and bacterial infection, scroll down to Step 1.

Method 1
Recognizing a Viral Infection

  1. Image titled Tell a Viral from a Bacterial Infection Step 1
    Know what a virus is. Viruses are basically some simple genetic material (nucleic acid) with a protein coat. They are not complete cells and therefore are smaller than bacteria. Viruses cannot reproduce on their own, so they must use the cells of a host body (in this case, us) to reproduce for them, usually killing the cell and making us sick in the process. The symptoms of a viral infection generally diffuse throughout the body, rather than causing pain or irritation in only one specific part of your body.[1]
    • As they cannot live and multiply on their own and are harmful to the host, they are considered parasitic.
  2. Image titled Tell a Viral from a Bacterial Infection Step 2
    Be aware of how long a viral infection lasts. Viral infections are self-limiting (which means that they generally go away on their own within 3 to 10 days). The first few days of the infection are usually the worst but you will see gradual improvement over time.
    • This is one of the best ways to know if you have a viral or bacterial infection--if your symptoms last for longer than a week without getting better, you most likely have a bacterial infection. However, symptoms lasting longer than 14 days can be a sign of a complication of the viral illness, such as a secondary bacterial infection.
    • For viral sinusitis, symptoms can last 3-4 weeks, but also will improve gradually over time.
  3. Image titled Tell a Viral from a Bacterial Infection Step 3
    Look for signs of a low-grade fever. One of the most common symptoms of a viral infection is a low-grade fever. When your body gets infected by a harmful organism (in this case a viral pathogen), it will increase its internal temperature in an attempt to burn out and destroy the virus. Fevers also help to slow down certain enzymes in your body that would otherwise unknowingly help the virus to multiply. However, when your body is responding to a virus, it generally keeps the fever at a low temperature.
    • Symptoms of a fever: Check your temperature using a thermometer; if your temperature is above 98.6ºF (37ºC), but below 100.4ºF (38ºC), you have a low-grade fever[2]. You might also experience sweating, shivering, muscle ache, a loss of appetite and generally feeling weak.[3]
  4. Image titled Tell a Viral from a Bacterial Infection Step 4
    Keep track of any pain in your head. Headaches will generally develop if you have a viral infection. Most of the time, a headache will come on if you have a fever or if your body is secreting some compounds that are making your insides inflamed.
    • Symptoms of a headache: With headaches brought on by viral infections, you will almost always feel them in the front of your head (your forehead). It can be a sharp, pulsing pain or a continual dull ache.
  5. Image titled Tell a Viral from a Bacterial Infection Step 5
    Look out for a runny nose. One of the most common symptoms of an upper-respiratory viral infection is getting a runny nose. You might have a lot of fluid dripping out of your nose or down your throat. Runny noses can also feel like your nose is stuffed up and you can’t get much air through your nose.
    • A runny nose can lead to a cough because the fluid draining out of your nose can drip down your throat (known as postnasal drip) and can irritate the lining of your throat and lungs, causing a cough.
  6. Image titled Tell a Viral from a Bacterial Infection Step 6
    Know that you might develop a cough. Sometimes, an upper-respiratory viral infection can lead to you developing an annoying cough. This is because your body is secreting extra mucus because of the virus. This mucus irritates and inflames the lining of your throat and lungs, causing a cough.
    • Symptoms of a cough: A cough caused by a viral infection will generally develop and get worse over the course of a day or two. It will generally be productive, meaning you will be coughing up phlegm or mucus. While your viral infection might clear up within a couple of days, your cough might last for up to four weeks because the inflammation in your throat takes longer to recover than the rest of your body.[4]
  7. Image titled Tell a Viral from a Bacterial Infection Step 7
    Look at the mucus that you cough up. While this might sound like a gross thing to do, the color of the phlegm (medically referred to as sputum) will help you figure out if you have a viral or bacterial infection. Sputum caused by a viral infection is almost always clear and runny.
    • Sputum caused by a bacteria infection is generally firm and can be yellowish, greenish, orange, or even rust-colored.
  8. Image titled Tell a Viral from a Bacterial Infection Step 8
    Watch out for a sore throat. Viral infections that affect your upper-respiratory tract (which encompasses your nose, nasal passages, and upper pharynx) generally lead to you having a sore throat. This is because the virus causes inflammation in your throat, which irritates the lining that covers your throat.
    • Symptoms of a sore throat: Your throat may feel swollen and you might feel pain when you swallow. Your throat might also feel scratchy or hot and irritated.
  9. Image titled Tell a Viral from a Bacterial Infection Step 9
    Monitor any feelings of fatigue you develop. When your whole body is putting its energy towards fighting off a viral infection, you are most likely going to feel very tired. The best thing you can do is give your body the rest it needs.
  10. Image titled Tell a Viral from a Bacterial Infection Step 10
    Be aware of whole-body muscle aches. Viral infections generally diffuse throughout the body, affecting your whole body rather than one specific part. One of the ways that a virus shows up throughout your body is by creating muscle aches. All of your muscles, from your head to your toes, will feel achy and tired.
    • Myalgia refers to pain that affects all of your muscles. Some people describe it as a muscle-crushing pain.
    • Arthralgia refers to joint pain that can also occur.
  11. Image titled Tell a Viral from a Bacterial Infection Step 11
    Check for a rash if your child is the one who is sick. Viral infections can cause a widespread rash to form. However, this generally only happens to children with a viral infection. The rash will generally appear red and bumpy. The viruses that create these rashes include:
    • Measles virus, Rubella virus, Parvovirus, and Human Herpes virus 6 and 7.
  12. Image titled Tell a Viral from a Bacterial Infection Step 12
    Look out for signs of a gastrointestinal virus. You also may experience some digestive symptoms like nausea, vomiting or diarrhea; these symptoms will appear if you have contracted a virus that affects your gastrointestinal system (including your stomach and intestines). Common gastrointestinal viruses include:
    • Rotavirus (this generally only infects children), Norovirus (this is the most common virus and is referred to as the stomach bug), Adenovirus (this also generally only infects children), and astrovirus (this is generally a shorter, milder stomach bug).[5]
  13. Image titled Tell a Viral from a Bacterial Infection Step 13
    Know what the symptoms of some specific viral infections are. While knowing the general symptoms of a viral infection can be very helpful, you might also want to know what some specific viral infections look like.
    • Respiratory viral infections: Common symptoms include runny nose, mild to moderate sore throat, cough, mild to moderate fever (less than 101ºF or 38.3ºC in adults), fatigue and general body aches.
    • Sinusitis (inflammation of the membranes within the sinuses) is also often caused by a viral infection. Symptoms of sinusitis include sinus headache, nasal congestion, cloudy or discolored drainage, sinus pressure and facial pain.
    • Gastrointestinal symptoms can include mild to moderate fever, fatigue, nausea, cramping and diarrhea.

Method 2
Recognizing a Bacterial Infection

  1. Image titled Tell a Viral from a Bacterial Infection Step 14
    Know what bacteria is and does. Where viruses are not complete cells and require a host, bacteria are typically single-celled organisms that can exist on their own without the benefit of a host (us). Bacteria exist in numerous places, including soil, water on our skin and within our bodies. Symptoms caused by a bacterial infection generally stay in one part of your body, rather than spreading throughout your body like a viral infection.[6]
    • Most bacteria are harmless and some are beneficial to us, such as the naturally occurring bacteria within our intestines that help us digest food. However, there are several common bacteria that can cause respiratory and gastrointestinal infections.
  2. Image titled Tell a Viral from a Bacterial Infection Step 15
    Know how long a bacterial infection lasts. In general, bacterial infections can last 5-14 days with medication depending on the type and site of infection. Your individual health and immune system will also affect how long you feel sick for. One common characteristic of bacterial infections is that they may actually get worse over time (as opposed to viral infections which tend to gradually get better each day). Bacterial infections will generally only go away if you take medication (usually antibiotics).
    • Any medical treatment received, such as antibiotics, will also affect the duration of the infection.
  3. Image titled Tell a Viral from a Bacterial Infection Step 16
    Look for a high-grade fever. While fevers are also a sign of a viral infection, bacterial infection fevers are generally high-grade, meaning that they are generally at or above 101ºF (38.3ºC). Your body will increase its internal temperature in an attempt to destroy the invading bacteria.
    • Symptoms of a high-grade fever that stays around 101ºF (38.3ºC): Sweating, chills, headache, muscle aches, feeling weak, and loss of appetite.
    • Symptoms of a high-grade fever between 103ºF and 106ºF (39.4ºC to 41.1ºC): Hallucinations, dehydration, convulsions, and irritability.
  4. Image titled Tell a Viral from a Bacterial Infection Step 17
    Watch out for pain felt in only one spot. Bacterial infections can cause really severe pain that is felt in only one part of your body. For example, if you have an ear infection, you might feel a very sharp, constant pain in only one of your ears (the ear with the infection).
  5. Image titled Tell a Viral from a Bacterial Infection Step 18
    Check to see if your lymph nodes are swollen. When your body tries to fight a bacterial infection, your lymph nodes begin to work overtime. This can cause them to become swollen. Your lymph nodes are located in your neck, directly below your ears, and in your armpits, elbow crease, groin, and behind the knee. To check your lymph nodes[7]:
    • Place your fingers over your lymph nodes located in front, below, and behind your ears. Rub them in a gentle circular motion. If they are swollen, they will feel firm and about the size of a pea. For more information on how to check your lymph nodes, click here.
  6. Image titled Tell a Viral from a Bacterial Infection Step 19
    Talk to your doctor about abscesses. An abscess is a swollen lump filled with pus that can form on the surface of your skin or on an internal organ, depending on where your bacterial infection is located. Abscesses are another way that your body fights an infection—white blood cells flock to the infection site and essentially do battle with the bacteria located there. The dead white blood and bacteria cells form the pus.
    • Symptoms of abscesses: Swelling (the abscess will look like a swollen bump), a reddish color, heat in and around the abscess, pain where the abscess is located, and potential loss of function of the spot where the abscess has formed.
  7. Image titled Tell a Viral from a Bacterial Infection Step 20
    Know the symptoms of specific bacterial infections. Symptoms related to bacterial infections can vary depending on the type of bacteria, the location of the infection and whether the infection is localized (just in one area) or has spread to become systemic (affects the whole body). It may be helpful to know the symptoms of some of the most common bacterial infections.
    • Strep throat: The symptoms are typically a sudden onset of a severe sore throat, a fever that is above 101 degrees F (38 degrees C), headache, nausea, swollen lymph nodes in your neck, inflamed tonsils that may have white spots and a light skin rash.
    • Bacterial sinusitis: These symptoms are similar to viral sinusitis although there may be fever and the nasal drainage may be a bright green or yellow in color.[8]
    • Bacterial pneumonia: This is a serious illness and is accompanied by high fever (101-104 degrees F), chest pain, shortness of breath, a deep productive cough, loss of appetite and severe fatigue.
    • Salmonella: Gastrointestinal symptoms of Salmonella include abdominal cramping, fever, (watery and bloody) diarrhea, vomiting, nausea and headache.
  8. Image titled Tell a Viral from a Bacterial Infection Step 21
    Know that bacterial infections may be the result of a "secondary" infection. In these cases, the infection started out virally and progressed to a bacterial infection. Here's how to tell this may be going on:[9]
    • A virus tends to last less than two weeks. These will persist longer.
    • Fever is higher than expected from a normal virus.
    • Instead of improving, the fever gets worse a few days into the illness .

Method 3
Seeking Medical Care

  1. Image titled Tell a Viral from a Bacterial Infection Step 22
    Treat the symptoms of a viral infection. While viruses will generally clear up on their own, you might want to treat the symptoms that could be causing you pain and discomfort.
    • Take acetaminophen (like Tylenol) or ibuprofen (like Advil) to reduce the pain caused by headaches and muscle aches. These medications will also lower your temperature if you have a fever.
    • Drink lots of water. Viral infections can make you very dehydrated so it’s important that you drink a lot of water to keep yourself hydrated. Drink more than eight glasses of water each day.
    • Sleep as much as possible. You will need to rest as much as possible so that you can put your body’s energy towards fighting the viral infection.
  2. Image titled Tell a Viral from a Bacterial Infection Step 23
    Go see a doctor if you think you have a bacterial infection. Ultimately, getting examined by a doctor is the most sure-fire way to figure out whether or not you have a bacterial infection. Your doctor will most likely take a small blood sample to examine the types of white blood cells present in your blood (your body uses different kinds of white blood cells to fight bacterial infections versus viral infections).[10]
  3. Image titled Tell a Viral from a Bacterial Infection Step 24
    Take antibiotics to treat a bacterial infection. Visit your doctor in order to get a prescription for antibiotics. The type of antibiotic will depend on the type of bacterial infection you have. Once you have the prescription, follow it through to the very end. This means taking a pill each day until the medication has run out, even if you start to feel better within the first couple of days. You need to complete the course of the antibiotics to ensure that the infection doesn’t come back.[11] Common antibiotics that are prescribed include:
    • For strep throat: amoxicillin, penicillin, cephalexin, and erythromycin.[12]
    • For bacterial sinusitis: Amoxicillin, trimethoprim-sulfamethoxazole, or Doxycycline.[13]
    • For very severe Salmonella: Ampicillin, fluoroquinolones, and third-generation cephalosporins.[14]
  4. Image titled Tell a Viral from a Bacterial Infection Step 25
    Know that some bacterial infections can be contagious (such as strep throat). In these cases, you should also seek medical care as treatment with antibiotics may be warranted. Once diagnosed and prescribed an antibiotic for a contagious bacterial infection, you should avoid direct contact with others for 24 hours after starting the antibiotic because you can give them the bacteria.
    • Once you do start the antibiotic, however, you will not be contagious. Another reason to seek treatment immediately!
  5. Image titled Tell a Viral from a Bacterial Infection Step 26
    Take caution, regardless of what you have. When you first get sick, wondering whether you have a simple cold (virus) or something more serious (such as strep throat or bacterial sinusitis) is very common. By understanding the similarities and differences between viral and bacterial infections, this may be a bit easier to determine. However, even doctors sometimes get confused. When in doubt, assume you're contagious and take care of yourself.


  • Getting the flu vaccine can help prevent you from getting viral infections.
  • The most common kinds of viruses include rhinoviruses (cold), rotaviruses (gastroenteritis), noroviruses (also gastroenteritis) and influenza viruses (flu).
  • One of the most common bacterial infections affecting our upper respiratory tract is strep throat, caused by group A Streptococcus bacteria.
  • Other bacterial infections include bacterial sinusitis and bacterial pneumonia (often caused by Streptococcus pneumoniae or Haemophilus influenzae).
  • Common gastrointestinal bacterial infections include food-borne Salmonella, diarrheagenic E. Coli infection (caused by several types of the Escherichia coli bacteria) and Clostridium perfringens food poisoning.


  • Go see a doctor right away if you think you have a bacterial infection.
  • If your symptoms worsen, visit your doctor. If symptoms worsen after getting better initially, symptoms become severe or do not gradually subside or you have systemic affects such as dehydration and low blood pressure, then you should seek medical care.
  • Get plenty of rest regardless of whether you have a viral or bacterial infection.

Article Info

Categories: Infectious Diseases