What Is the Difference Between Viral and Bacterial Infection?

Both can make you sick, but here's what separates the two.

Both a virus and bacterium are smaller than the naked eye can see. But they have more differences than just their size. 

You may know that a virus can cause a cold or COVID-19, and bacteria can lead to foodborne illnesses. Still, you may not know much more about those submicroscopic dangers. 

Viruses and bacteria are all around us. While we can't see them, they can make themselves known if they infect us. Here's what you should know about the differences between viruses and bacteria and why it's important to understand them.

What Are Viruses?

Viruses are microorganisms made of genetic material called nucleic acids, either DNA or RNA, and surrounded by a coat of protein, Charles Bailey, MD, infectious disease specialist based in California, told Health.

Viruses can take over the cells in your body. When infected, viruses use your cells to make copies of their genetic material. The virus multiplies, overtakes other cells, and continues to reproduce. That process can damage or kill your healthy cells, leading to illness.

Some infectious illnesses caused by viruses include:

  • Common colds
  • COVID-19
  • Flu 
  • Warts
  • Human immunodeficiency virus (HIV)
  • Ebola

What Are Bacteria?

In contrast, bacteria—larger (but still submicroscopic), single-celled microorganisms—don't need a host to reproduce. Bacteria are capable of living in various types of environments, said Dr. Bailey.

The human body is full of bacteria. Your gut microbiome balances healthy and harmful bacteria and regulates your gut health.

But some bacteria cause illness by replicating quickly in our bodies, damaging or killing cells and tissues. Many disease-causing bacteria produce toxins, powerful chemicals that damage cells and make you sick.

Some infectious illnesses caused by bacteria include:

  • Staphylococcal (staph) infections, like skin infections, food poisoning, and pneumonia
  • Streptococcus (strep) infections, like strep throat, scarlet fever, and impetigo
  • E. coli infections, like food poisoning

Viruses vs. Bacteria: What Is the Difference?

"When people wonder what the difference is between a virus and bacteria, it's like comparing the difference between a roach and a shark," Theresa M. Fiorito, MD, a pediatric infectious disease specialist at NYU Langone Hospital—Long Island, told Health. "There are many differences: where they live, what they eat, and—probably what's most relevant to us—how to kill them." 

One thing viruses and bacteria have in common is that they both have the potential to cause infections and lead to mild, moderate, or severe illness.

Bacteria and viruses are different in terms of molecular structure. Still, they can cause infections with similar symptoms, such as fever, sore throat, and cough. Those symptoms vary depending on the specific infection and how severe it is.

"In recent years, as well as throughout history, we have seen pandemics and epidemics caused by viruses [like the COVID-19 pandemic] and bacteria," said Dr. Bailey.

When a virus causes an illness, it is known as a viral infection. And when a bacterium causes an illness, it is known as a bacterial infection.

Secondary Infections

Although bacterial and viral infections are different, they have some connections. For instance, viral respiratory infections can sometimes lead to bacterial infections. Changes in the immune system may cause those secondary infections.

A study published in 2021 in Scientific Reports found that of 642 patients hospitalized with COVID-19, 12.6% developed a bacterial infection. And of 742 patients hospitalized for the flu, 8.7% developed a bacterial infection.

That secondary bacterial infection—commonly caused by Staphylococcus bacteria—increases the risk of death. Staphylococcus bacteria causes pneumonia after having a viral illness, like the cold, flu, or COVID-19.

Common Colds and the Flu: Viral or Bacterial?

The common cold is one of the most prevalent viral illnesses globally. There are over 200 different viruses responsible for colds. But rhinoviruses are usually the culprit. Other viruses that cause colds include:

  • Respiratory syncytial virus (RSV)
  • Parainfluenza viruses
  • Adenoviruses
  • Coronaviruses
  • Metapneumoviruses

Like the common cold, the flu is also a viral illness. There are two main types of flu viruses: types A and B. Most commonly, the flu spreads during the fall and winter months.

Both the cold and the flu have similar symptoms, including:

  • Stuffy, runny nose
  • Sneezing
  • Sore throat
  • Cough
  • Chest discomfort
  • Muscle aches and pains
  • Fatigue
  • Fever, which are more common with the flu than colds

Because those symptoms are similar, it can be difficult to tell the difference between a cold and the flu. In general, flu symptoms feel more severe than the cold.

How Viruses and Bacteria Spread

How do viruses and bacteria infect people in the first place? Well, depending on the type, viruses can spread through the following modes:

  • Skin-to-skin contact
  • Respiratory secretions, like a cough or sneeze
  • Droplets when someone speaks or breathes
  • Vomit, diarrhea, urine, or feces (either through the particles in the air or if someone contaminates food with it)
  • Saliva
  • Semen or vaginal discharge
  • Blood

Additionally, most people come in contact with bacteria through the following modes:

  • Direct contact with an infected person or animal
  • Contact with bacteria in the air or droplets
  • The bite of an insect, such as an infected tick
  • Contaminated food, water, or utensils

Treating Viral and Bacterial Infections

You might require treatment if infected with a virus or bacterium and become sick. But how viruses and bacteria respond to medication is another difference between them.

"Viruses are treated by antiviral agents, while bacteria are treated by antibacterial agents [antibiotics]," said Dr. Bailey.

Some examples of antivirals that treat viral illnesses include:

  • Tamiflu (oseltamivir) treats the flu.
  • Remdesivir can treat COVID-19.
  • Biktarvy (bictegravir/emtricitabine/tenofovir alafenamide) is a combination of antiretroviral drugs that treat HIV.

And some examples of antibiotics—all of which can treat various bacteria-caused infections—include:

  • Amoxicillin
  • Doxycycline
  • Cephalexin

"Bacteria have cell walls and internal structures that can be targeted by antibiotics to either kill the organism or interrupt its life cycle," explained Dr. Bailey. "Viruses are simpler with fewer structural targets. But since they must enter into other cells to reproduce themselves, this offers antiviral agents an opportunity to work by interfering with these elements of the viral life cycle."

The Centers for Disease Control and Prevention (CDC) also points out that antibiotics are not always needed to treat all bacterial infections. For instance, many bacteria-caused sinus infections and some ear infections typically get better on their own.

Taking antibiotics when unnecessary provides no benefit and might even result in harmful side effects, like antibiotic resistance.

How To Protect Yourself

Personal hygiene is key for protecting against both bacteria and viruses. For example, regular handwashing helps get rid of any germs that live on your hands.

Vaccination is another way to protect yourself against both bacteria and viruses. According to Dr. Bailey, some viral and bacterial illnesses that you can prevent with vaccines include:

  • Viral infections: COVID-19, the flu, mumps, and polio
  • Bacterial infections: Pertussis, diphtheria, tetanus, pneumococcal pneumonia, and meningococcal disease

As such, the CDC recommends sticking to a regular, up-to-date immunization schedule to protect yourself against those illnesses.

Per the National Library of Medicine, covering up your coughs and sneezes and wearing personal protective equipment (like masks and globes) can also help.

You can also eliminate viruses and bacteria by sanitizing and disinfecting objects. According to the Environmental Protection Agency (EPA), you can use chemicals that sanitize surfaces to kill bacteria, not viruses. In contrast, disinfecting gets rid of both microorganisms. The EPA regulates products to ensure that what you're using is effective.

When To See a Healthcare Provider

If you feel ill and think you might have an infection, consulting a healthcare provider can confirm a diagnosis. Seeing a healthcare provider is especially important if you experience symptoms like:

  • Fever, which is sometimes the only sign of an infection
  • Chills and sweats
  • Change in cough or a new cough
  • Sore throat or new mouth sore
  • Shortness of breath
  • Nasal congestion
  • Stiff neck
  • Burning or pain while urinating 
  • Unusual vaginal discharge or irritation
  • Redness, soreness, or swelling in any area, including surgical wounds and ports

If you have an infection, a healthcare provider can determine whether it's viral or bacterial. To do that, a healthcare provider will ask about your symptoms. 

Additionally, they might run diagnostic tests, like taking samples of your urine, stool, or blood or a swab from your nose or throat. The results can help a healthcare provider determine how to best treat your infection.

A Quick Review

While viral and bacterial infections share similarities, it is important to know their differences for prevention, diagnosis, and treatment. Both can cause infections with similar symptoms but vary depending on the infection and its severity.

Personal hygiene, vaccination, and sanitizing methods are some of the best ways to prevent infection with either germ. If you feel ill and think you might have an infection, a healthcare provider can determine your infection and how to treat it.

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Health.com 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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