Bacterial vs. Viral Infection: Tips for Identification and Treatment

Bacteria and viruses are often the cause of common infections. However, they differ in structure and life cycle, infection types, and treatment methods, making the management and treatment different for each. With the antimicrobial resistance crisis currently gaining momentum, it is becoming more important than ever to be able to distinguish between viral and bacterial infection.

What are bacterial infections?

Bacterial infections are caused by microscopic, single-cell organisms (microbes, more commonly known as ‘germs’) called bacteria, which invade the body. Various different kinds of bacteria cause diseases, called pathogenic. Common bacterial infections include urinary tract infections (UTIs), pneumonia, Lyme disease, tetanus, salmonella infection, and streptococcal infections including strep throat. Bacteria are transmitted to humans through air, water, food, or direct and indirect contact. Bacteria can also be passed from mother to baby during pregnancy, childbirth, or breastfeeding, and through insect bites. Common bacteria include:

  • Streptococcus spp
  • Salmonella spp
  • Clostridium difficile spp
  • Staphylococcus spp

What are viral infections?

Viral infections are also caused by microscopic infectious agents (microbes), which invade host cells (such as cells within the human body) and replicate and spread. Viruses cause diseases such as the common cold, influenza (flu), measles, chickenpox, COVID-19, herpes simplex virus (HSV), and gastroenteritis. Viruses are also accountable for AIDS and SARS. Viral infections have multiple modes of transmission, similar to those of bacteria, including air, droplets, direct contact, food, water, or insect bites. Viruses typically enter the human body through one of numerous portals of entry, including the skin, respiratory tract, gastrointestinal tract, genital tract, eyes, or placenta. Common viruses include:

  • Influenza virus
  • Human respiratory syncytial virus (RSV)
  • Measles
  • Varicella-zoster virus (VZV)
  • Herpes simplex virus (HSV)
  • Human papillomavirus (HPV)

Bacterial vs. viral infection: what’s the difference?

Bacteria consist of single cells capable of surviving on their own, both in and outside the body. Most bacteria carry a single molecule of DNA, which carries all the information needed for reproduction. Alternatively, some bacteria also contain additional genetic elements such as plasmids which aid in this process of reproduction, survival, or infection.

The majority of bacteria are not harmful, and numerous beneficial species of bacteria live on and within the body, particularly in the gastrointestinal tract, aiding in important bodily functions such as digestion, immune system response, and skin and oral health. However, harmful bacteria can cause infection by producing harmful substances called toxins, invading tissues, or both.

Viruses are tiny, ranging in size from about 20–400 nanometers in diameter, billions of which can fit into the head of a pin. Viruses lack cellular structure, consisting of genetic material, either DNA or RNA, enclosed in a protein shell. Unlike bacteria, viruses rely on a living host, such as a human or animal, to multiply. Viruses initiate infection by infiltrating and replicating within the healthy cells of the body. Understanding these differences is vital for the development of effective treatments and preventive measures against viral and bacterial infections.

Infection symptoms

The symptoms of viral infection often have a more gradual onset, resolving on their own over time, while bacterial infections may have a more rapid onset, typically persisting longer without treatment.

Typical symptoms of both can include:

  • Fever
  • Chills
  • Sore throat
  • Nasal congestion
  • Runny nose
  • Body aches

Some symptoms are more typical of viral infection than bacterial, and vice versa. For example, some viral infections can cause a characteristic rash. Bacterial infections may result in higher-grade fever than viral infections, and some bacterial infections cause redness, swelling, and pain in specific infected areas of the skin. However, as many of the symptoms overlap, it is important to seek medical advice, especially if symptoms persist and become severe.

Often, bacterial infections can be secondary infections, meaning the virus or other pathogen came first, and bacteria followed. In these instances, the symptoms get progressively worse rather than better and are more severe, especially when left untreated. Some bacterial infections can result in severe complications such as sepsis, pneumonia, or meningitis, which can adversely affect multiple organ systems. Some viral infections that remain untreated can result in more severe and persistent infections and complications, and some remain in the body for life. One specific example of this is when HIV is left untreated, it can become AIDS.

Diagnosis of viral or bacterial infections

Diagnosis of viral or bacterial infections is multifaceted and includes a physical exam, symptom history, analysis of recent travel, and diagnostic tests.

Diagnostic tests include blood tests, throat swabs, or cultures. Other tests can be utilized based on the presenting symptoms, which include urine tests, saliva or mucus cultures, and X-rays.

Certain tests can help differentiate between viral and bacterial pathogens, allowing targeted treatments to be prescribed, such as bacterial culture and drug sensitivity testing, blood cultures, polymerase chain reaction (PCR), or rapid antigen tests. Some infections have very specific physical symptoms that make them easier to diagnose, such as measles or chickenpox, abscesses, or urinary tract infection.

Treatment of viral or bacterial infections

The treatment for viral and bacterial infections varies significantly.

Treating viral infection

When it comes to treating viral infections, there is often no specific treatment; treatment is focused on relieving any associated symptoms. In the majority of cases, treatment can be managed at home, through the use of supportive care and home remedies, including:

  • Drinking plenty of water to prevent dehydration
  • Resting
  • Taking over-the-counter pain medications, such as paracetamol, to relieve any aches, pain, or fever
  • Taking over-the-counter cold decongestants if advised by your healthcare professional

In some cases, antiviral medication can be prescribed, which may impede the life cycle of the virus, inhibiting virus attachment to healthy host cells, virus entry, or disrupting viral replication machinery. The use of antivirals can be discussed with your healthcare professional.

Active immunization by vaccine has been a globally useful strategy in preventing common epidemics caused by highly infectious viruses. One common example of this is the influenza (flu) vaccine, recommended by the Centers for Disease Control and Prevention.

Treating bacterial infection

Antibiotics are the mainstay of medications used to treat bacterial infections and may be prescribed when a bacterial infection is not going away with other management techniques. Not all bacterial infections require antibiotics. Some mild bacterial infections such as ear or sinus infections may resolve with home management techniques, emphasizing the importance of appropriate antibiotic use and the role of healthcare professionals in determining when antibiotics are required.

Antibiotics work by killing bacteria or stopping them from multiplying by affecting crucial parts of their structure needed to survive.

Doctors often classify bacterial infections as being caused by gram-negative or gram-positive bacteria. This distinction is important to note because each classification often requires treatment with different types of antibiotics.

In some cases, bacterial infection can lead to severe or life-threatening complications, resulting in hospitalization and intensive care management. Examples include severe pneumonia, meningitis, and sepsis. In such cases, IV antibiotics, IV fluids, and intensive care treatment may be required. Bacterial and viral pathogens differ in structure and life cycle, infection types, and treatment methods.

Antimicrobial resistance: global health crisis

According to the World Health Organization (WHO), antimicrobial resistance is one of the top global public health threats, estimated to be directly responsible for 1.27 million global deaths in 2019, and a contributing factor in around 4.95 million deaths.

Antimicrobial resistance arises when bacteria, viruses, fungi, and parasites lose their sensitivity to antimicrobial medications, rendering antibiotics, antiviral, and antifungal treatments ineffective. This antibiotic resistance can make infections extremely challenging or even impossible to treat.

One of the most common causes of antimicrobial resistance is the overuse of these medications, specifically the misuse of antibiotics to treat viral infections. To appropriately prescribe tailored treatment and limit antimicrobial resistance, it is extremely important to distinguish between bacterial and viral infection.

Stay informed

Distinguishing between viral and bacterial infections can be difficult due to their similar symptoms. Common infections encompass a wide range of illnesses and include respiratory infections, gastrointestinal infections, urinary tract infections, skin and soft tissue infections, ear infections, sexually transmitted infections, and eye infections.

Antibiotics do not work on viruses, which are fundamentally different from bacteria in their structure, replication mechanisms, and biochemical processes, because of which antibiotics do not affect them.

Staying informed of the differences between bacterial and viral infection ensures a proactive approach to infectious disease management and utilization of healthcare and will help reduce the impact of antimicrobial resistance on public health outcomes around the world.


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