When people are sick, the last thing they want is a science lesson, but sometimes it can be important to understand if the illness was caused by a virus or by bacteria. The most important reason why it matters is because the treatment options are often different.

The Commonalities

Most obviously, both bacterial and viral infections can be extremely unpleasant and even dangerous to your health. These infections can be latent, acute, or chronic, and they can range from mild to fatal.

Bacteria and viruses are both microbes. They can be spread through coughing and sneezing; contact with infected people, pets, livestock, or pests; and/or contact with contaminated food, water, or surfaces.

The Differences

Bacteria are single-celled organisms and they are fairly complex. Most bacteria have a rigid wall, a fluid center, and a thin rubbery membrane surrounding that fluid center. They can reproduce on their own and they are able to survive challenges such as extreme temperatures and radioactive waste. Fossils show that bacteria have been in existence for at least 3.5 billion years.

Viruses are much smaller than bacteria, and they consist of a core of genetic material (either RNA or DNA) surrounded by a protein coat. They cannot survive without a host and they cannot reproduce on their own. They do attack specific cells in the human body and they can even attack bacteria.

Why They Matter

Both bacterial and viral infections can produce similar symptoms, such as fever, inflammation, aches and cramps, nausea and vomiting, and diarrhea. Some diseases, such as pneumonia and meningitis, can be caused by either bacteria or viruses. Tests such as blood tests, urinalysis, culture tests, and biopsies can be used to determine the origin of an illness.

Viral infections do not respond to antibiotics, but bacterial infections do. Antibiotics have saved many millions of lives, but the overuse of antibiotics can lead to antibiotic-resistant disease strains. It is important to only prescribe antibiotics when they can help, such as when an infection is clearly bacterial, and this is why it is important to know the cause of the illness.