Viral vs. Bacterial Infection: What’s the Difference?

Viral and bacterial infections can both make you sick. Symptoms of viral and bacterial infections can range from mild to severe. Without treatment, some can even threaten your life.

A viral infection is an illness caused by a virus. Common viral infections include COVID-19, influenza (the flu), and chicken pox. Bacterial infections are caused by bacteria. These types of germs cause ailments that include strep throat, tetanus, and anthrax.

While all illnesses have many things in common, it's important to find out what germ you have to get the treatment you need. When you are sick, antibiotics can kill bacteria, but not viruses. It is one of the key ways these two germ types differ.

This article contains details about the ways these infections vary and how they affect your body. It also highlights symptoms, treatments, testing, and ways to prevent them.

Woman shielding herself from a virus

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Difference Between Viruses and Bacteria

Viruses and bacteria are two types of microscopic pathogens. While both types of germs can trigger an immune response and produce similar symptoms, their structures and the ways they react to medication set them apart from each other.

Viruses vs. Bacteria

A key difference between viruses and bacteria is that antibiotics are effective against bacteria, not viruses. Antibiotics do not work on viruses.

Viruses are infectious parasites that require a living host to survive and multiply. They are the smallest germs, whose only components include genetic material encased in protein. When viruses infect a host, they grow and reproduce inside the cells. In doing so, they can damage, kill, or change the cells they infect.

Viruses also have the following characteristics:

  • Smaller than the smallest bacteria
  • Specific to the area of the body they attack
  • Can't survive without a host cell or from an animal, human, or plant

Bacteria are single-celled organisms that exist and reproduce almost anywhere alone. Most bacteria don't make you sick. Our bodies naturally have about 10 times more bacterial cells than human cells, many of which support your digestive system.

Other characteristics of bacteria include:

  • Able to live on its own without a host
  • Can cause illness after a viral infection, creating a secondary infection
  • Can exist for weeks to months on surfaces or materials, depending on the type of bacteria

Viral vs. Bacterial Infection Diagnosis

Getting an accurate diagnosis of a bacterial or viral infection requires laboratory testing. This is usually conducted by a healthcare provider.

The type of specimen collected depends on the type of germ that is suspected. Specimens collected to confirm viral or bacterial diagnosis are often taken from one of the following areas:

  • Throat
  • Rash
  • Nose
  • Urine
  • Stool
  • Vomit
  • Sputum
  • Blood
  • Wound
  • Body tissue
  • Vomit
  • Spinal fluid

Viral Infections

Diagnosing viral infections is most commonly done by virological tests that look for the virus's DNA or RNA (genetic makeup) in the sample. Some tests identify antibodies that your body has made against a virus after the incubation period. When antibodies of a specific virus are found, it can indicate that you have immunity to the virus.

Nucleic acid amplification tests (NAATs) are generally accurate and highly sensitive. They are regarded to test for viral infections. Other tests used to identify viruses include:

Bacterial Infections

Diagnosis of a bacterial infection often involves the use of a bacteria culture test. This test involves taking a sample of your urine, blood, or tissue from the site where you are having symptoms. The sample is then sent to a lab. There, the cells are allowed to grow for a couple of days until there is enough to test for the presence of bacteria.

A blood test called a complete blood count (CBC) may also be used to diagnose a bacterial infection. This test measures counts for white blood cells, red blood cells, and blood platelets. In searching for an infection, your healthcare provider will review your white blood cell count because these cells increase when they are fighting an infection.

When a specific infection is suspected, your blood test may be ordered as a CBC with differential. This can help specify the number of each type of white blood cell in your blood so the infection can be identified. This is key to getting the right treatment for the infection involved.


While they occur from different types of germs, viral infection symptoms and bacterial infection symptoms are often similar in the early phases of illness. This is why it's necessary to use laboratory testing to confirm the source of your disease.

Common symptoms of both types of infections include:

Common Viral Infections

With so many different viruses and bacteria, it's difficult to determine what type of germ is causing your symptoms without a medical exam. Some diseases, like meningitis, can be caused by either bacteria or viruses. Though people may exhibit symptoms differently based on age and general health, a bacterial infection may be suspected when the illness has the following characteristics:

  • Symptoms that last longer than the 10 to 14 days that are typical with a virus
  • A fever that is higher than the temperature of one that occurs with a virus
  • A fever that worsens rather than improving over time

Common Bacterial Infections

Examples of common bacterial infections include:


The method for treating viral vs. bacterial infections is one of the key factors that distinguish these two types of infections. Treating an infection caused by a virus is more challenging than treating one caused by bacteria.

Antibiotics are powerful drugs that kill or stop the growth of certain infections caused by bacteria. They can treat serious bacterial infections like sepsis and pneumonia. They can also treat common infections like UTIs, strep throat, and Escherichia coli (E. coli).

Examples of antibiotics include:

Because antibiotics are so powerful, many patients seek them out for the treatment of any type of infection. However, taking antibiotics for a viral infection is useless and can even threaten your health. It can increase your risk of side effects and antibiotic resistance, a situation in which bacteria are no longer vulnerable to the antibiotics designed to kill them.

There are no equivalents to antibiotics for viral infections. While some viral infections can be treated with antiviral drugs, these are disease-specific drugs and are ineffective against other diseases caused by viruses. When effective, these drugs work in slowing viral replication.

Examples of antiviral medications include:

  • Tamiflu (oseltamivir) for influenza
  • Valtrex (valacyclovir) for herpes simplex or herpes zoster

Treatment for most viral infections involves the management of symptoms while your immune system works to fight the infection.


Preventing the transmission of viral and bacterial infections can be challenging. Many infections are contagious and can be spread through person-to-person or indirect contact before symptoms occur.

The following steps can help prevent the spread of viral and bacterial infections:

  • Get vaccinated for viral and bacterial infections and ensure that your vaccination status remains current with boosters.
  • Wash your hands thoroughly and often.
  • Cover a cough or sneeze into your elbow.
  • Pay attention to food safety when storing and preparing food.
  • Avoid close contact with wild animals.
  • Practice safer sex by always using a condom in every intimate encounter.
  • Don't share items like combs, toothbrushes, glasses, and straws.


Viral and bacterial infections are caused by germs. While these germs differ in the way they attack your body, they can both make you sick with symptoms that can range from mild to severe. Getting a lab test is often the only way to diagnose your illness.

Finding out which type of germ is making you sick is key to getting the right treatment. If your illness is caused by bacteria, antibiotics can kill the germs and make it hard for them to grow. If a virus is causing your sickness, you may have to wait for your immune system to fight the germs while you take steps to ease your symptoms.

You can reduce your risk of these types of ailments by taking steps to prevent the spread of disease. Vaccines can prevent or reduce the impact of the germs they target. Other safeguards, like washing your hands and having safe sex, can also reduce your chances of catching these ailments.

A Word From Verywell

Viral and bacterial infections are so common that it's likely you've had several by the time you reach adulthood. That doesn't mean that you should take your symptoms lightly any time they occur.

Without a physical exam and lab test, it's usually not possible to diagnose the source of your illness. Knowing the type of germ causing your infection helps your provider determine whether you can benefit from an antibiotic, a treatment that only works on bacterial infections.

These powerful drugs aren't effective against viruses, but if you have a virus, your provider can recommend ways to stay comfortable and reduce your symptoms. If you have one of a few specific viruses, you may qualify for treatment with an antiviral drug.

If you recognize symptoms of a viral or bacterial infection, contact your healthcare provider to find out whether testing is advised based on your symptoms and other factors about your health. This can give you the best chance of feeling better faster.

Frequently Asked Questions

  • What are the signs of a viral infection?

    Signs of a viral infection vary based on the type of virus you have and how your body reacts. Common symptoms include fever, muscle aches, cough, sore throat, nasal congestion, and/or headache. Symptoms can last from three days to around a week, then get better on their own.

  • Do antibiotics treat viral infections?

    Antibiotics only treat bacterial infections. They don't work against viral infections. Taking antibiotics for a viral infection can increase your risk of side effects and contribute to antibiotic resistance.

  • What is the main difference between a bacterial infection and a viral infection?

    The main difference between a bacterial infection and a viral infection is that a bacterial infection can be treated with antibiotics. A viral infection is usually left to run its course, with treatments often only used to help alleviate symptoms. Some viral infections can be treated with antiviral medications.

19 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Anna Giorgi
Anna Zernone Giorgi is a writer who specializes in health and lifestyle topics. Her experience includes over 25 years of writing on health and wellness-related subjects for consumers and medical professionals, in addition to holding positions in healthcare communications.