Infectious disease is a major cause of social and economic instability, with pathogenic bacteria and viruses accounting for most cases worldwide. That said, colonization does not necessarily cause infectious disease, as some viruses and bacteria can multiply within the body without causing harm.

Bacteria and viruses exert their effect in similar ways, for example, by killing cells. However, bacteria can also cause the body to mount an excessive immune response, which in itself can cause significant damage to the body.

In order to reduce the rate of bacterial and viral infections, scientists spend a lot of time learning how these pathogens interact with the body. Only then can they sufficiently prevent or treat the spread of disease.

Read on to learn more about the difference between bacterial and viral infections.

Bacteria and viruses are two types of microbes. The table below outlines the differences between them.

Bacteria Viruses
10–100 times larger than viruses Very small and are 20–40 nanometers (nm) in diameter
Some are treated with antibiotics Some are treated with antiviral medications
Reproduce by dividingEnter a living organism’s cells and use the cell’s machinery to reproduce

Initially, the body responds in a similar way to a bacterial or viral infection.

Early symptoms usually indicate the body is trying to rid itself of a pathogen. A high temperature, for example, can inactivate viruses and help to denature bacteria, which is why fever is an initial infection symptom.

Another immune response is to produce more interferon, a substance that plays a part in the body’s defense system. Interferon helps to stop viruses and bacteria from reproducing. However, in concentrated amounts, it can make someone feel tired and achy.

venn diagram showing differences in viral and bacterial infectionsShare on Pinterest
Infographic by Bailey Mariner

Common differences between bacterial and viral infections are the following:

Bacterial infection

Key signs include:

  • symptoms lasting longer than 10–14 days
  • fever can become exceptionally high
  • fever gets worse over time rather than improving

Viral infection

Key signs include:

  • if due to influenza virus (“the flu”), symptoms respond well to antiviral medication (within the first 48 hours)
  • fever eases with time
  • fever is uncomfortable but usually not dangerous

Bacterial infection occurs when one or more bacteria have entered the body and begin to multiply. However, not all bacterial infections cause disease.

Bacteria have evolved to evade or manipulate the body’s immune system. So when pathogenic bacteria enter the body, they:

  • release toxins
  • may multiply very quickly to dominate an area
  • kill cells
  • can lead to a dangerously high immune response

Common bacterial infections include:

Bacterial skin infections

Staphylococcus and Streptococcus cause skin infections, such as:

  • impetigo
  • cellulitis
  • methicillin-resistant Staphylococcus aureus (MRSA)

Bacterial respiratory infection

Streptococcus pneumoniae bacterium commonly causes pneumonia.

Pneumonia presents with lung inflammation and is a very serious and sometimes lethal infection.

Other symptoms include:

  • fever
  • coughing up blood
  • labored breathing
  • breathlessness
  • rapid heartbeat

Bacterial sexually transmitted infections (STIs)

Bacterial STIs include:

  • chlamydia
  • gonorrhea
  • mycoplasma genitalium
  • syphilis
  • bacterial vaginosis

Viruses are packets of DNA or RNA encased in a protein shell.

Outside of the body, they lack the ability to reproduce. However, upon entering a living organism, the virus invades its cells and seizes control over the cell’s metabolic machinery to make copies of itself.

After the virus makes enough copies, the cell bursts releasing them to infect more cells.

There are many different types of viral infections.

Viral skin infections

Common viral skin infections include:

  • chickenpox
  • molluscum contagiosum
  • shingles
  • roseola

Viral respiratory infections

Common respiratory viruses include:


According to the Centers for Disease Control and Prevention (CDC), there are multiple different types of coronavirus. Some cause minor cold-like symptoms, while others result in severe health complications.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a new type of coronavirus. People exposed to the SARS-CoV-2 virus may go on to develop the novel coronavirus disease (COVID-19).

Influenza and cold viruses

Influenza viruses cause influenza, also called “the flu.” People who get flu typically experience:

People with a common cold experience less severe symptoms and rarely develop fever.

Viral STIs

Viral STIs include:

  • HIV
  • hepatitis B virus
  • herpes simplex virus
  • human papilloma virus (HPV)

Bacteria and viruses move from one person to another by:

  • Touch: If people do not wash their hands, they can transmit bacteria and viruses onto other surfaces, including food.
  • Droplets: When a person sneezes or coughs, they create droplets that carry viruses and bacteria, which another person can inhale.
  • Injury: Some bacteria and viruses enter the body through cuts and puncture wounds.

To determine if a person has a viral or bacterial infection, a doctor will usually ask questions about their symptoms and perform a physical exam.

To confirm a diagnosis, they may request tests, such as:

  • Enzyme-linked immunosorbent assay (ELISA): This test can help to detect infection due to many viruses, including HIV and bacterial infections such as Lyme disease.
  • Polymerase chain reaction (PCR): This test sequences the DNA of microorganisms, and can detect viral infections, such as HPV, in addition to bacterial infections including, Escherichia coli (E. coli).
  • Electron microscopy: This type of imaging can be used to identify rare viral and bacterial infections that require high resolution to detect. However, because electron microscopy is an expensive diagnostic tool, doctors rarely request it.

Treatment for bacteria and viruses is different, and consequently, a prompt diagnosis is very important.


Antibiotics are medicines that either kill or stop bacteria from reproducing.

Different types of antibiotics target different bacterial infections. Antibiotics are not effective against viral infections.

Antibiotics are available in the following forms:

  • oral forms, such as pills, capsules, and liquids
  • ear drops and eye drops
  • topical forms, such as creams, ointments, and sprays

If the infection is more severe, a doctor may recommend an antibiotic injection, intravenous infusion, or drip.


Antiviral drugs are medicines that work to stop viruses from reproducing. Each antiviral medication usually works on one specific virus or only a group of viruses.

Remdesivir was the first antiviral to receive approval for the treatment of COVID-19 in October 2020.

Preventing bacterial and viral infections is the best action to take to stop the spread of disease.

Steps people can take to protect themselves include:

  • washing their hands
  • bandaging cuts
  • covering their mouths when they cough or sneeze
  • receiving vaccinations
  • seeking advice before traveling to tropical destinations

Bacteria and viruses are different types of microorganisms, and some cause disease.

Doctors typically use antibiotics to treat bacterial infections and antivirals for some viral infections. However, some infections are untreatable.

The best way to prevent any type of infection is with good hygiene. Vaccines are an effective method for preventing certain viral and bacterial infections.

A person should speak with their doctor if they think they have an infection.