Infectious diseases are illnesses caused by harmful agents (pathogens) that get into your body. The most common causes are viruses, bacteria, fungi and parasites. Infectious diseases usually spread from person to person, through contaminated food or water and through bug bites. Some infectious diseases are minor and some are very serious.
Infectious diseases are illnesses caused by harmful organisms (pathogens) that get into your body from the outside. Pathogens that cause infectious diseases are viruses, bacteria, fungi, parasites and, rarely, prions. You can get infectious diseases from other people, bug bites and contaminated food, water or soil.
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Infectious diseases are caused by harmful organisms that get into your body from the outside, like viruses and bacteria. Noninfectious diseases aren’t caused by outside organisms, but by genetics, anatomical differences, getting older and the environment you live in. You can’t get noninfectious diseases from other people, by getting a bug bite or from your food.
The flu, measles, HIV, strep throat, COVID-19 and salmonella are all examples of infectious diseases. Cancer, diabetes, congestive heart failure and Alzheimer’s disease are all examples of noninfectious diseases.
Infectious diseases can be viral, bacterial, parasitic or fungal infections. There’s also a rare group of infectious diseases known as transmissible spongiform encephalopathies (TSEs).
Infectious diseases are extremely common worldwide, but some are more common than others. For instance, each year in the United States, 1 out of every 5 people is infected with the influenza virus, but less than 300 people are diagnosed with prion diseases.
Some of the most common infectious diseases are listed here by type.
Anyone can get an infectious disease. You may be at an increased risk if your immune system is weakened or if you travel to areas with certain highly transmissible diseases.
People at higher risk of infectious disease include:
Many infectious diseases resolve without complications, but some can cause lasting damage.
Serious and life-threatening complications of various infectious diseases include:
Symptoms of infectious diseases depend on the type of illness. Fungal infections usually cause localized symptoms, like rash and itching. Viral and bacterial infections can have symptoms in many areas of your body, like:
It’s important to see a doctor if you have any chronic (ongoing) symptoms or symptoms that get worse over time.
Infectious diseases are caused by a variety of agents that invade your body from the outside. These include:
You may develop symptoms when your cells are damaged or destroyed by the invading organism and as your immune system responds to the infection.
Depending on the type of infection, there are many ways that infectious diseases can spread. Fortunately, in most cases, there are simple ways to prevent infection.
Your mouth, your nose and cuts in your skin are common places for pathogens to enter your body. Diseases can spread:
Your healthcare provider usually diagnoses infectious diseases using one or more lab tests. Your provider can look for signs of disease by:
Some test results, like from a nose swab, come back quickly, but other results might take longer. For instance, sometimes bacteria has to be grown in a lab (cultured) from a sample before you can get your test result.
Treatment depends on what causes the infection. Sometimes your healthcare provider will recommend monitoring your symptoms rather than taking medication.
Antibiotic resistance is when bacteria develop mutations that make it harder for our medicines to destroy them. This happens when antibiotics are overused, such as for minor infections that your body could fight off on its own.
Antibiotic resistance makes some bacterial infections very difficult to treat and more likely to be life-threatening. Methicillin-resistant Staphylococcus aureus (MRSA) is an example of a bacterial infection that has become antibiotic-resistant.
Healthcare providers are working to reduce antibiotic resistance. You can help — and protect yourself — by finishing all of your antibiotic medication as prescribed. This helps to make sure all of the bacteria are destroyed and can’t mutate.
There are many simple ways to reduce your risk of infectious disease and even prevent certain illnesses altogether. While each of these helps to reduce your risk of getting and spreading infectious diseases, often there’s no single way that’s 100% effective at preventing disease. That’s why it’s important to have many habits for reducing your risk.
You can think of it as lining up slices of Swiss cheese, a model suggested by James Reason, PhD. Where some slices have holes, other slices give protection. Getting recommended vaccinations, and simple habits like practicing safe food handling and washing your hands, work together to give you layers of protection.
Vaccines reduce your risk of getting an infectious disease by training your immune system to recognize and fight off infections from harmful invaders. While people sometimes do still get sick with a disease after getting vaccinated for it, your symptoms are usually less severe than they would’ve been without the vaccination.
Usually given as a shot or series of shots (or, less commonly, as a nasal spray), vaccines are available for many common infectious diseases, including:
The CDC has up-to-date recommendations for vaccinations for children, adolescents and adults. If you’re traveling, make sure you have all of the recommended vaccinations for your destination before you go.
Safe food handling habits help prevent certain infectious diseases.
In addition to vaccines and safe food handling habits, you can reduce your risk of coming down with or spreading an infectious disease with a few everyday practices.
With treatment, most people get better after being sick with an infectious disease.
Sometimes there can still be serious complications, especially with respiratory illnesses. People with compromised immune systems are more at risk for serious complications, but they can happen in healthy people too.
Some diseases, like HIV and hepatitis B, can’t be cured, but medications can help prevent serious complications. Sexually transmitted infections can cause infertility or even lead to cancer, so it’s important to take steps to protect yourself and others.
Prion diseases are very serious and can’t be cured. They are fortunately some of the rarest infectious diseases.
Let your healthcare provider know if you have any symptoms of an infectious disease, especially if they’re unusual or don’t go away over time. If you have an ongoing infection, frequent follow-ups with your provider can help ensure your condition doesn’t worsen.
Your provider should also know if you plan to travel to foreign countries. You may need to be vaccinated against infections that are more common at your destination.
Emerging infectious diseases are those that are new or are infecting more people than they had previously. Special research is dedicated to these diseases. Some emerging infectious disease agents include Ebola, salmonella, hepatitis A, certain coronaviruses and West Nile virus.
Babies and children can be more likely to get sick from infectious diseases because their immune systems are still developing. They also can’t practice good hygiene on their own like adults can. Some infectious diseases that can be more common in children include:
A note from Cleveland Clinic
We coexist with viruses, bacteria, fungi and parasites every day. In fact, you have 10 times more bacteria inside your body than human cells — we couldn’t live without them!
Some of the organisms that we come across can be harmful. Fortunately, there are many simple things you can do to keep yourself healthy.
It’s also important to remember that there might be people around you who aren’t able to fight off infections easily. Washing your hands, covering your mouth when you cough or sneeze and other simple habits can help protect others from getting seriously ill. A small habit for you could be life-saving for someone else.
Last reviewed by a Cleveland Clinic medical professional on 06/06/2022.
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