Viral Infection or Bacterial Infection? Know the Difference

You are feverish with a wicked sore throat, stuffed up nose, and body aches. Last time you had a sore throat and fever, the doctor prescribed you an antibiotic and you felt better after two or three days of taking the medicine. This time, however, after the examination, she simply instructs you to take ibuprofen for pain, to get plenty of rest and fluids, and let your body fight it off, which might take several days.

You have almost identical symptoms to the last time you were ill, so why no antibiotic this time? Because last time, your doctor found evidence of a bacterial infection (let’s say it was strep throat), but this time, the lab tests for a bacterial infection came back negative. Your doctor diagnoses you with the flu and tells you that an antibiotic won’t help you. Ever wonder why?


Bacteria are microscopic single- celled organisms that can thrive in just about any environment. They can survive on their own, whether inside or outside other living organisms.

Most bacteria are harmless, and some are actually good for us by helping us digest food and destroying disease-causing cells (including certain types of cancer). In fact, fewer than 1% of bacteria cause diseases in people.

Viruses are also microscopic organisms, even smaller than bacteria, but they behave differently. Scientists
even debate whether viruses should actually be called living organisms. Unlike bacteria, viral cells cannot grow or
reproduce independently from living cells. While many viruses might be able to live for a brief time outside of their host (e.g., on a doorknob immediately after an infected person touches it or in the air right after someone sneezes), they can only flourish inside of a living thing, whether plant, animal, or bacteria. Also, unlike bacteria, most viruses do cause disease and are very specific regarding the cells they attack.


After entering the body, unwanted bacteria quickly begin to divide and spread, disrupting the normal functioning of the host tissue and/ or, in some cases, destroying the host tissue. Strep throat and urinary tract infections are examples of infections caused by bacteria. Bacteria can kill host cells and destroy tissues outright and even make toxins in our body that can paralyze, disrupt the proper functioning of cells, or cause a massive immune reaction that is itself toxic to the host body. Your doctor can usually identify a bacterial infection using lab tests. For example, to determine if your sore throat is actually strep, the doctor will swab the back of your throat and do a throat culture to check for the presence of the streptococcus bacteria.

If your test is positive for a bacterial infection, that’s when the doctor usually prescribes the antibiotic. An antibiotic will kill the bacteria. Viruses also make us sick by killing cells and/or disrupting cell function. However, once a virus gets in your body, the viral cells must latch onto and then recode healthy cells, so that instead of doing what they are supposed to do, they will produce viral particles and replicate the viral cells. Some viruses can be treated with antiviral medication; however, antivirals cannot eliminate viruses the way antibiotics do bacteria; antivirals can only ease symptoms and prevent viral replication…It’s up to the host body’s immune system to actually destroy the viral invaders. Also, unlike unhealthy bacteria, once you’ve been infected by a certain virus, after your body initiates the immune response, part of that response entails “remembering” that virus. Thus, if you are ever exposed to that particular virus again, your body knows exactly what to do and can fight off the infection much more quickly than it did the first time (i.e., you become immune to that virus). But you can be infected with the same type of bacteria over and over again, particularly if your immune system has been weakened.

Sometimes, a bacterial infection will occur as a “secondary” infection, meaning that you were infected with a virus first and then a bacterial infection followed. You should suspect that a bacterial infection has joined the viral infection party in your body if 1) symptoms of illness worsen or persist longer than the expected 10 to 14 days that symptoms of a virus tend to last, and/or 2) your fever returns and/or gets worse after a few days rather than improving.

At that point, you should go see the doctor so that she can test you for a bacterial infection and prescribe an antibiotic, if necessary.

While symptoms of a bacterial infection might be similar in a number of ways to symptoms of a viral infection (for example, they both can cause sore throats, vomiting, diarrhea, fever, and coughing), there are also some differences:

  1. Symptoms of a viral infection tend to be less severe than those of a bacterial infection, but
    they can last longer. For example, with a viral infection, you’ll probably feel better in 2 or 3 days, but you might hang onto a bit of a cough for 7 to 10 days. On the other hand, with a bacterial infection, symptoms tend to be more severe, but clear up more quickly once you’ve been treated with an antibiotic (for a normally healthy person, usually within 2 to 3 days); the symptoms shouldn’t linger.
  2. Mucus from a viral infection tends to be clear, whereas mucus from a bacterial infection tends to be dark greenish or brownish in color.
  3. Bacterial infections of the throat typically cause pussy white spots to appear inside your throat; viruses usually don’t. Also, sore throats due to viral infections tend to come with other symptoms, like a stuffed up nose and cough, whereas if the sore throat is caused by
    a bacterial infection, the sore throat and fever are usually the only symptoms.
  4. With a viral infection, fevers tend to go away on their own after
    2 or 3 days; however, with an untreated bacterial infection, fevers usually get worse and you feel sicker as time goes on.

Remember! If you are prescribed an antibiotic, it is important to take all of the medicine as prescribed. This will ensure that the bacterial infection is completely eliminated. If you don’t finish the course of antibiotics as prescribed, it’s likely that not all of the bacteria will be eliminated. The remaining bacteria can then develop their own immunity to the antibiotic, allowing them to thrive again and become resistant to additional antibiotic treatment. An antibiotic-resistant strain of bacteria is much harder to eliminate, and you might have to take several rounds of different antibiotics before the unhealthy bacteria is killed off. This can be particularly dangerous in those individuals with an already weakened immune systems, such as those with HIV/AIDs or the elderly). Antibiotic resistance has become a world-wide problem.

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