Viral Infection
Illness caused by a virus invading the body's cells
Quick Facts
- Type: Infectious illness caused by a virus
- Examples: Cold, flu, COVID-19, stomach viruses
- Spread: Air, droplets, contact, fluids, food, or water
- Antibiotics: Do not work against viruses
Overview
A viral infection is an illness caused by a virus, a tiny germ that can only multiply by entering the cells of a living host. Once inside the body, a virus hijacks cells to make copies of itself, which can damage those cells and trigger the immune system to respond. The symptoms of a viral infection often come from this immune response as much as from the virus itself.
Viruses cause a huge range of illnesses, from common, self-limiting conditions like colds and many sore throats to more serious diseases. Because viruses are very different from bacteria, antibiotics do not work against them. Most everyday viral infections improve on their own with rest and supportive care, while some are prevented by vaccines or treated with specific antiviral medications.
Symptoms
Symptoms depend on which virus is involved and which part of the body it affects, but common patterns include:
- Respiratory viruses: Runny or stuffy nose, sore throat, cough, fever, and body aches.
- Stomach and intestinal viruses: Nausea, vomiting, diarrhea, and cramping.
- General symptoms: Fever, chills, fatigue, headache, and muscle aches.
- Skin-related viruses: Rashes or blisters with certain infections.
Most viral infections are mild and resolve within days to a couple of weeks. Warning signs that need prompt medical care include difficulty breathing, a very high or persistent fever, confusion, signs of dehydration, severe pain, or symptoms that worsen instead of improving.
Causes
Viral infections are caused by viruses, which spread from person to person or from the environment in several ways:
- Respiratory spread: Breathing in droplets or small particles from someone who coughs, sneezes, or talks.
- Contact spread: Touching a contaminated surface or an infected person and then touching the face.
- Food and water: Consuming contaminated food or water, common with stomach viruses.
- Body fluids: Through blood or other body fluids for certain viruses.
- Insect bites: Some viruses are spread by mosquitoes or ticks.
How easily a virus spreads and how serious it is varies widely from one virus to another.
Risk Factors
- Close contact with infected people, especially in crowded settings
- A weakened immune system from illness, age, or medications
- Being very young or very old
- Not being up to date on recommended vaccines
- Poor hand hygiene or contaminated food and water
- Travel to areas with certain viral diseases
Diagnosis
Many viral infections are diagnosed based on symptoms and a physical examination, especially for common illnesses like colds. When more information is needed, doctors may use:
- Laboratory tests: Swabs, saliva, blood, or stool tests that detect a specific virus or the body's antibodies against it.
- Rapid tests: Quick tests for certain viruses such as influenza and COVID-19.
- Other tests: Imaging or additional testing when complications such as pneumonia are suspected.
Identifying the specific virus is most useful when it changes treatment, guides prevention, or is needed for a serious illness.
Treatment
Treatment depends on the virus and the severity of illness. For most common viral infections, care is supportive:
- Rest and fluids: Allowing the body to recover and staying well hydrated.
- Symptom relief: Fever reducers and pain relievers, decongestants, and other measures to ease discomfort.
- Antiviral medications: Available for some viruses, such as influenza, certain herpes infections, hepatitis, HIV, and COVID-19, and most helpful when started early or used for higher-risk people.
- Hospital care: For severe infections or complications.
Antibiotics do not work against viruses and should not be used for viral illnesses, although a doctor may prescribe them if a bacterial infection develops on top of a viral one.
Prevention
- Wash hands often and avoid touching your face
- Stay up to date on recommended vaccines, which prevent many serious viral infections
- Cover coughs and sneezes and stay home when sick
- Avoid close contact with people who are ill when possible
- Handle and prepare food safely and use clean water
- Use protection against insect bites in areas with mosquito- or tick-borne viruses
When to See a Doctor
Most viral infections can be managed at home, but see a doctor if symptoms are severe, last longer than expected, or keep getting worse. Seek urgent or emergency care for:
- Difficulty breathing or shortness of breath
- A very high fever or a fever that will not come down
- Confusion, severe headache, or a stiff neck
- Signs of dehydration, such as little urine, dizziness, or no tears in children
- Severe or persistent vomiting or diarrhea
People with weakened immune systems, infants, older adults, and pregnant people should seek care earlier, as they are at higher risk for complications.
Frequently Asked Questions
Why don't antibiotics work for viral infections?
Antibiotics target bacteria, which are very different from viruses. Viruses multiply inside the body's own cells, so antibiotics have no effect on them. Using antibiotics for viral illnesses does not help and can contribute to antibiotic resistance.
How are viral infections treated?
Most common viral infections are treated with rest, fluids, and medicines to ease symptoms like fever and aches. Some viruses have specific antiviral medications, which work best when started early or used for people at higher risk of complications.
How do viral infections spread?
They spread through respiratory droplets and small particles, contact with infected people or contaminated surfaces, contaminated food or water, body fluids, and, for some viruses, insect bites. How easily each virus spreads varies widely.
How can I tell a viral infection from a bacterial one?
It can be hard to tell from symptoms alone, since both can cause fever and feeling unwell. A doctor considers the pattern of illness and may use tests to identify the cause, which helps decide whether treatments like antivirals or antibiotics are appropriate.
When should I see a doctor for a viral infection?
Seek care if symptoms are severe, worsening, or last longer than expected, or if you have difficulty breathing, a very high fever, confusion, or signs of dehydration. People with weakened immune systems, infants, and older adults should seek care earlier.
References
- Centers for Disease Control and Prevention (CDC). Viruses and how they spread.
- MedlinePlus, U.S. National Library of Medicine. Viral infections.
- Mayo Clinic. Infectious diseases.
- World Health Organization (WHO). Antimicrobial resistance.