Infection

An infection happens when harmful germs enter your body, multiply, and cause your body to react. These tiny organisms—bacteria, viruses, fungi, or parasites—can trigger symptoms ranging from mild discomfort to life-threatening illness.

Table of contents

• What Is an Infection?
• Types of Infections
• Common Symptoms
• How Infections Spread
• Who Is at Higher Risk?
• Diagnosing Infections
• Treatment Options
• Prevention Strategies

What Is an Infection?

An infection occurs when microscopic organisms known as pathogens (disease-causing germs) enter your body from outside, multiply, and cause your body to react^[1]. These harmful organisms invade tissues, increase in number, and often produce toxins (poisonous substances) that damage cells and make you sick^[2].

Not all germs cause infections. In fact, many microorganisms live naturally in and on our bodies without causing harm. Some are even helpful, supporting functions like digestion and protecting against harmful invaders^[3]. However, under certain conditions, even normally harmless bacteria can cause disease if they multiply in the wrong place or if your immune system is weakened^[4].

Infections caused by pathogens are also called infectious diseases, transmissible diseases, or communicable diseases^[1]. They remain a significant global health concern, causing approximately 9.2 million deaths in 2013, which represented 17% of all deaths worldwide^[1].

Types of Infections

Infections are classified by the type of pathogen that causes them. Each type of germ behaves differently in the body and requires different treatment approaches^[4].

Bacterial infections are caused by single-celled organisms called bacteria. These microorganisms have their genetic instructions written on a small piece of DNA^[2]. While many bacteria are harmless or even beneficial, pathogenic bacteria can cause diseases such as strep throat, tuberculosis, urinary tract infections, and food poisoning^[10]. Antibiotics are the primary treatment for bacterial infections^[1].

Viral infections are caused by viruses, which are pieces of genetic material (DNA or RNA) protected by a protein shell^[2]. Viruses are the most common cause of infections in humans^[4]. After entering your body, a virus invades your cells and uses the cell’s components to make copies of itself^[7]. Common viral infections include colds, flu, COVID-19, and respiratory syncytial virus (RSV)^[2]. Unlike bacterial infections, antibiotics do not work against viruses^[7].

Fungal infections occur when fungi that normally live on your body or in your environment overgrow or get into places where they shouldn’t be^[2]. Common examples include athlete’s foot, ringworm, and yeast infections^[2]. Antifungal medications are used to treat these infections^[1].

Parasitic infections are caused by parasites, which are organisms that live off other living things^[2]. Examples include hookworms, pinworms, and other parasitic worms^[2]. Treatment typically involves antiprotozoal or antihelminthic medications^[1].

Prion diseases are extremely rare infections caused by faulty proteins that make other proteins become faulty too. These are also called transmissible spongiform encephalopathies^[2].

Common Symptoms

The symptoms of an infection depend on where in your body the infection is located and what type of pathogen is causing it^[2]. However, many infections share some general warning signs.

Common symptoms include fever, which signals that your body is fighting the infection^[5]. You may also experience fatigue, feeling tired or unwell, and muscle aches throughout your body^[2]. Other frequent symptoms are chills, faster heartbeat, headache, and night sweats^[5].

Respiratory infections often cause coughing, runny or stuffy nose, sore throat, and difficulty breathing^[2]. Digestive infections can lead to diarrhea, nausea, vomiting, and loss of appetite^[2]. Skin infections may cause rashes, itching, redness, or swelling in specific areas of your body^[2].

Many symptoms occur not directly from the pathogen itself, but from your immune system’s response to the infection^[4]. When germs damage or destroy cells and your immune system responds, this creates the symptoms you feel^[2].

You should seek medical care immediately if you have been bitten by an animal, have trouble breathing, cough for more than a week or cough up yellow-green mucus or blood, have a severe headache with fever, or develop a widespread rash that comes with fever, leaks fluid, or feels painful or warm^[5].

How Infections Spread

Understanding how infections spread can help you protect yourself and others. Germs can travel from person to person or from the environment to people through several routes^[3].

Airborne and droplet transmission occurs when an infected person coughs, sneezes, talks, or sings, creating tiny respiratory droplets that contain germs^[9]. These droplets can land on your eyes, nose, or mouth if you’re nearby, or you might breathe them in^[3]. Common colds, flu, and COVID-19 spread this way^[9].

Direct contact transmission happens when you touch someone who is infected or touch surfaces and objects that have germs on them, then touch your mouth, nose, or eyes without washing your hands first^[2]. Healthcare workers can spread infections by touching contaminated medical equipment and then touching a patient before cleaning their hands^[3].

Food and waterborne transmission occurs when you eat or drink contaminated food or water^[2]. This is a common way to get infections like salmonella and other types of food poisoning^[10].

Vector transmission happens through bug or animal bites when infected insects or animals transfer germs to you^[2]. Examples include Lyme disease spread by ticks^[10].

Other transmission routes include contact with cuts, scrapes, or broken skin, through sexual contact, from a pregnant person to their baby, through blood transfusions or organ transplants, and from contaminated soil or water during activities like gardening or in areas affected by flooding^[2][8].

Who Is at Higher Risk?

Anyone can get an infection, but certain factors increase your risk of becoming sick or developing serious complications^[2].

People with weakened immune systems are more vulnerable to infections. This includes individuals with conditions like HIV, cancer, or those who have received organ transplants^[3]. If your immune system is compromised, it’s harder for your body to fight off pathogens^[2].

Certain medications can decrease your body’s ability to fight infections. These include antibiotics (which can disrupt your normal protective bacteria), steroids, and some cancer-fighting medications^[3].

Medical treatments and procedures can provide additional ways for germs to enter your body. Urinary catheters, breathing tubes, intravenous lines, and surgery all increase infection risk^[3].

Underlying medical conditions such as diabetes, heart disease, or chronic lung disease can make it more difficult for your body to defend against infections^[2][3]. Age also matters: infants, children, and older adults are at higher risk^[18].

Diagnosing Infections

Proper diagnosis of an infection is essential for choosing the right treatment. Your healthcare provider will likely ask about your symptoms and medical history, and perform a physical examination^[11].

Laboratory tests are the most common way to identify infections. Blood tests can detect signs of infection and identify specific pathogens^[11]. Urine tests help diagnose urinary tract infections and other conditions^[11]. Throat swabs can identify strep throat and other respiratory infections, while stool samples can check for parasites and other organisms in digestive infections^[11].

A spinal tap (lumbar puncture) may be performed if meningitis or another infection of the brain or spinal cord is suspected. This procedure uses a needle to take a sample of the fluid surrounding your brain and spinal cord^[11].

Imaging tests help healthcare providers see inside your body to identify infections. X-rays, computerized tomography (CT) scans, ultrasound, and magnetic resonance imaging (MRI) can all reveal signs of infection in different parts of your body^[11].

Biopsy involves taking a tiny sample of tissue for testing. For example, a lung tissue biopsy can be checked for various fungi that cause certain types of pneumonia^[11].

Different types of diagnostic tests help identify the specific pathogen causing your infection, which ensures you receive the most effective treatment^[11].

Treatment Options

Treatment for infections depends on the type of pathogen causing the illness. Knowing which type of germ is responsible makes it easier for your healthcare team to choose the right treatment^[11].

Antibiotics are medicines that clear up bacterial infections. They work by killing bacteria or stopping them from reproducing, allowing your body’s natural defenses to eliminate the pathogens^[12]. Different antibiotics work against different types of bacteria. Some are broad-spectrum antibiotics that work against many types of bacteria, while others are narrow-spectrum and target specific bacterial species^[13]. It’s crucial to take antibiotics exactly as prescribed, even after you start feeling better, to ensure all bacteria are eliminated^[12]. Antibiotics do not work against viral infections^[1].

Antiviral medications are used to treat some viral infections. Unlike antibiotics, antivirals work by inhibiting a virus’s ability to reproduce rather than killing it directly^[12]. However, only a few viral infections have effective antiviral treatments available^[4].

Antifungal medications treat fungal infections by targeting the fungi causing the illness^[1]. These medications come in various forms including pills, creams, and intravenous treatments, depending on the location and severity of the infection.

Antiprotozoal and antihelminthic medications are used for parasitic infections. Antiprotozoals treat infections caused by protozoa, while antihelminthics eliminate parasitic worms^[1].

For mild infections, your immune system may be able to fight off the pathogen without medication. Rest, increased fluid intake, proper nutrition, and time allow your body’s natural defenses to work^[13]. Many viral infections are self-limiting, meaning they run their course as your body attacks and removes them^[4].

Treatment may also focus on relieving symptoms while your immune system fights the infection. This supportive care can include pain relievers, fever reducers, rest, and staying hydrated^[4].

Prevention Strategies

Preventing infections is the best way to protect yourself and others from illness. Many simple, effective strategies can significantly reduce your risk of getting sick^[17].

Hand hygiene is the single most important way to prevent infections. Wash your hands frequently with soap and warm water for at least 20 seconds^[17]. Be sure to clean your fingertips, under your nails, between your fingers, and the backs of your hands^[17]. Always wash your hands after using the bathroom, blowing your nose, coughing or sneezing, before preparing or eating food, after touching animals, and after caring for someone who is sick^[17]. If soap and water aren’t available, use an alcohol-based hand sanitizer with at least 60% alcohol^[3].

Respiratory hygiene helps prevent spreading infections to others. Cover your mouth and nose with a tissue when you sneeze or cough, then throw the tissue away^[17]. If no tissue is available, cough or sneeze into your elbow rather than your hands^[17].

Vaccination is one of the most effective ways to prevent infectious diseases. Vaccines protect against many serious infections including measles, chickenpox, flu, COVID-19, and others^[5][12]. Stay up to date on recommended vaccinations for your age and health status^[23].

Food safety practices prevent foodborne infections. Rinse all meat, poultry, fish, fruits, and vegetables under running water before cooking or serving^[17]. Wash your hands with soap and water before and after handling raw meat. Keep raw and cooked foods separate, and don’t use the same utensils or cutting boards for both without washing them between uses^[17].

Avoiding close contact with people who are sick reduces your exposure to germs^[5]. Don’t share dishes, glasses, eating utensils, napkins, or tissues with others, especially when someone is ill^[17].

Proper wound care prevents infections from entering through broken skin. Wash and bandage all cuts promptly. Any serious cut or animal or human bite should be examined by a doctor^[17]. Don’t pick at healing wounds, blemishes, or pimples^[17].

Healthy lifestyle habits strengthen your immune system. Get adequate sleep—most adults need about seven to eight hours per night^[22][23]. Eat a balanced diet with plenty of fresh fruits and vegetables to ensure you’re getting essential vitamins and minerals^[22]. Stay hydrated by drinking approximately eight glasses of water daily^[23]. Incorporate regular exercise into your daily routine^[23]. If you smoke, quit—smoking increases your risk of infections and worsens symptoms^[23].

Avoid touching your face, especially your eyes, nose, and mouth, without washing your hands first. These areas are entry points for germs^[22].