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What is a viral infection?
Viral infections are illnesses you get from tiny organisms that use your cells to make more copies of themselves (viruses). Viral infections commonly cause respiratory and digestive illnesses, but viruses can also infect most other parts of your body.
What is a virus?
A virus is a type of germ (pathogen) that’s so small, you can only see it under a microscope. All viruses carry a small piece of genetic information (DNA or RNA) inside a protective coating (capsid). You can think of it like an envelope carrying instructions. Our cells, on the other hand, are like an entire factory: They contain instructions and all the equipment needed to carry them out. These instructions tells us how to build proteins and make more cells.
Unlike you and me, viruses don’t have cells, which means they don’t have all the “machinery” they need to make more of themselves. So, if they want to make copies of their instructions (replicate), they have to break into our cells and use our machinery to do it. Viruses replicating is what makes you sick with a viral infection.
How do you tell if a disease is viral or bacterial?
Viruses and bacteria can cause similar symptoms, like fever, cough and rashes. The only way to know what kind of infection you have is to have a healthcare provider assess you. If you have symptoms that last more than a few days or that concern you, see your provider.
What are the types of viral infections?
You might hear viruses described by what part of your body they infect, how they spread or what symptoms they cause. Some viruses, like herpes viruses and adenoviruses, can cause many different types of illness. Types of viral infections include:
- Respiratory infections.
- Digestive system infections.
- Viral hemorrhagic fevers.
- Sexually transmitted infections (STIs).
- Exanthematous (rash-causing) infections.
- Neurological infections.
- Congenital infections.
Respiratory infections affect your nose, throat, airways and lungs. Many respiratory viruses can cause bronchitis, sinusitis, ear infections or pneumonia. Examples include:
- Common cold (usually caused by rhinovirus).
- The flu (influenza).
- Respiratory syncytial virus (RSV).
- Human metapneumovirus (hMPV).
Viral infections in your digestive system
Viral infections in your digestive system can affect your stomach and intestines (GI tract) or your liver. These include:
- Norovirus, rotavirus and astrovirus can cause gastroenteritis, sometimes called “stomach flu.”
- Hepatitis viruses cause liver disease. These infections often last a long time (chronic).
Viral hemorrhagic fevers
Hemorrhagic fevers affect how your blood clots and can weaken your blood vessels, causing potentially life-threatening bleeding. Examples include:
Sexually transmitted viruses
Sexually transmitted diseases are mainly spread by sexual contact, including oral, anal and vaginal sex. Examples include:
- Human immunodeficiency virus (HIV).
- Human papilloma virus (HPV)/genital warts.
- Genital herpes (HSV).
- Hepatitis B.
Exanthematous viral infections
Exanthematous viral infections cause rashes that can appear as bumps or blisters on your skin or spots of blood under your skin. They can also cause respiratory or other symptoms. Examples of exanthematous infections include:
Some viruses attack the cells of your nervous system (your brain and spinal cord). These can cause paralysis, swelling of your brain or its covering (encephalitis or meningitis) and other life-threatening conditions. Examples include:
Congenital viral infections
Congenital viral infections are those you’re born with. They pass from a pregnant person to the fetus while it’s developing or during birth. Depending on the virus, this can cause various health issues, including vision or hearing loss, developmental delays and neurological conditions. Viruses known to cause congenital infections include:
- Cytomegalovirus (CMV).
- Zika virus.
Who do viral infections affect?
All of us will get viral infections at some point. But you’re at increased risk of serious illness from certain types of viruses if you:
Symptoms and Causes
What are the symptoms of a viral infection?
Symptoms of a viral infection depend on where you’re infected, but some common ones include:
- Flu-like symptoms: fever, head and body aches, fatigue.
- Upper respiratory symptoms: sore throat, cough, sneezing.
- Digestive symptoms: nausea, vomiting, diarrhea.
- Skin conditions: rashes, sores, blisters, warts.
Many viral infections don’t cause any symptoms.
What causes viral infections?
Many different types of viruses can cause infections, though only a few infect humans. They can get into your body through your nose, mouth, eyes, anus or genitals, or through a break in your skin. Once there, they get inside of your cells and use them to make more copies of themselves.
How do you get a viral infection?
Common ways you can get viral infections include:
- From other people (through coughing, sneezing or close contact).
- From surfaces or objects that someone with a virus has touched (like countertops, doorknobs or phones).
- Through vaginal, oral or anal sex.
- From a bite from an infected animal, mosquito or tick.
- From eating contaminated food or swallowing contaminated water.
Are viral infections contagious?
Yes, nearly all viral infections are contagious (can spread from person to person). Viruses need to infect living things to reproduce, so human viruses survive by spreading between people.
Diagnosis and Tests
How are viral infections diagnosed?
A healthcare provider can often diagnose you with a viral infection by listening to your symptoms and examining you. To diagnose a specific virus, your provider might swab your nose or throat or take a blood sample for testing.
If they think you have a viral infection causing serious inflammation in your lungs, brain or another internal organ, your provider might get X-rays, ultrasound, MRI or CT imaging. Imaging can’t diagnose a viral infection, but it can help your provider understand how it’s affecting your body.
Tests for viral infections
Your provider might send body fluid or tissue samples to a lab to look for signs of a viral infection (viral DNA/RNA, antibodies or antigens). Types of samples they might take include:
- Spit (saliva).
- Phlegm or mucus (sputum).
- Cells from your nose or nasopharynx (nasal/nasopharyngeal swab).
- Skin or other affected tissue.
- Fluid around your brain and spinal cord (CNS fluid).
- Pee (urine).
- Poop (stool).
- Cells from your cervix (Pap smear). Pap smears can find HPV, a virus that can cause cancer. The kind of HPV that can lead to cancer doesn’t usually have symptoms.
Management and Treatment
How are viral infections treated?
Specific medications are only available for a few viral infections. For viruses that can cause life-threatening or chronic illness, a provider may prescribe antiviral medications or treatment that prevents you from getting sick after being exposed to a virus.
For infections that rarely cause serious illness, like the common cold, you can usually treat the symptoms at home while you wait for them to go away on their own.
What medications are used to treat viruses?
Medications a healthcare provider might prescribe to treat viral infections include antiviral medications, convalescent plasma and post-exposure prophylaxis.
Antiviral medications stop viruses from making more copies of themselves (replicating). They can be used to manage chronic infections or shorten the length of some respiratory infections. They can only treat one type of virus — they don’t work on other viruses. Antivirals are available for the flu, COVID-19, hepatitis B and C, HIV and mpox.
In some cases, providers can treat someone with a life-threatening viral infection with a blood transfusion. For convalescent plasma treatment, someone who has recovered from an infection with the same virus donates their blood. Your provider gives you the plasma from the blood through an IV. The plasma contains antibodies, which help you fight the infection. Providers have treated some cases of COVID-19 and Ebola with convalescent plasma.
Treatments for certain life-threatening viral infections can prevent you from getting sick after being exposed. A provider has to give you these treatments before you have symptoms. These include antiviral medications and immunoglobulin (antibody) treatment. Post-exposure prophylaxis is available for:
- Hepatitis B.
Do antibiotics work on a viral infection?
No, antibiotics can’t treat or cure illnesses caused by a virus. You provider will only give you antibiotics if they think you have a bacterial infection.
How do I manage my symptoms?
If you have a mild respiratory or GI tract infection without complications, you can often manage the symptoms at home. Using over-the-counter (OTC) medications, drinking plenty of fluids and getting enough rest can help get you through until you’ve fought off the virus. It’s always a good idea to ask a healthcare provider what medications are OK to take.
How can I prevent viral infections?
One of the best ways to reduce your risk of a viral illness is to get vaccinated. A healthcare provider can tell you which vaccinations are recommended for you. Vaccinations are available for:
- Hepatitis A.
- Hepatitis B.
- Human papillomavirus (HPV).
- Flu (influenza).
- Measles, mumps and rubella.
Other ways to protect yourself and others from viruses include:
- Wash your hands frequently, especially during cold and flu season.
- Practice safe food habits. This includes storing food properly, heating meat and poultry to a safe temperature, and washing or peeling fruits and vegetables before eating.
- Use a condom or dental dam during any kind of sex.
- Protect yourself from bug bites. Wear protective clothing, use bug spray and sleep under mosquito netting if necessary.
- Don’t handle wild or aggressive animals. Don’t leave your pets outside unsupervised, where they could potentially get bitten by an animal with rabies.
- Avoid being around other people if you’re sick.
- Get post-exposure prophylaxis. If you’ve been exposed to certain viruses, post-exposure prophylaxis can prevent you from getting a life-threatening illness. Talk to a provider right away if you think you’ve been exposed to rabies, HIV, hepatitis B or chickenpox.
Outlook / Prognosis
What can I expect if I have a viral infection?
What to expect depends on what kind of viral infection you have. You can usually manage less serious infections, like the common cold or skin infections, at home. Other viral infections can cause life-threatening or long-lasting illness.
How long do viral infections last?
Viral infections can vary a lot in how long they last, for instance:
- Respiratory infections can last a few days to two weeks.
- A wart on your skin can last for a year or longer.
- Hepatitis B and C can cause chronic infections that last for years.
- HIV infections aren’t curable and are lifelong.
Complications of viral infections
Viral infections can cause serious complications, both shortly after getting sick or years later. Complications include:
- Inflammation in your lungs (pneumonia). Respiratory illnesses can infect your lungs and cause swelling that can make it hard to breathe. You may have to be treated in the hospital for severe pneumonia.
- Inflammation in your brain or its lining (encephalitis or meningitis). If a virus moves to your brain from another part of your body, it can cause swelling. This can be life-threatening.
- Severe bleeding. Hemorrhagic illnesses, like severe dengue, can cause life-threatening bleeding.
- Reactivation. Some viral infections can stay in your body for a long time, even if you no longer have symptoms — or you never had symptoms at all. A virus that’s not reproducing or causing symptoms in your body is called dormant. Viruses like Epstein-Barr (EBV), HPV, herpes simplex and varicella can reactivate in your body and cause symptoms years later.
- Cancer. Some viruses that stay in your body for long periods of time can cause cancer (oncoviruses). HPV, Epstein-Barr, HIV, hepatitis B and C, human T-lymphotropic virus 1 (HTLV-1) and human herpesvirus 8 (HHV-8) have all been linked to specific cancers.
When should I see my healthcare provider?
Contact a healthcare provider if:
- You have symptoms of a viral infection that aren’t getting better or are getting worse after several days.
- You have symptoms of the flu or COVID-19 and are at risk for serious illness. Your provider may be able to treat you with antiviral medications.
- You’ve been exposed to HIV, rabies, hepatitis B or chickenpox. You need post-exposure prophylaxis as soon as possible after exposure.
When should I go to the ER?
Go to the nearest ER or seek immediate medical attention if you have signs of a serious infection, including:
- High fever (103 degrees Fahrenheit/39.4 degrees Celsius).
- Difficulty breathing.
- Chest pain.
- Coughing up blood.
- Severe stomach (abdominal) pain.
- Confusion or other mental changes.
What questions should I ask my doctor?
- How do I prevent spreading this to other people?
- How do I use my medication?
- How long will it take to feel better?
- What can I do to manage my symptoms at home?
- When should I follow up with you?
A note from Cleveland Clinic
Viral infections are common and usually not serious. We manage colds, the occasional stomach bug, and bumps and sores on our skin on a regular basis. But some viruses cause life-threatening illnesses, and some common illnesses — like the flu — can turn serious. This is why it’s important to take steps to protect yourself and those around you from viral infection. Vaccinations, good hand-washing habits and safe sex can all help you stay healthy.
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