What Is an Infection?

It’s important for you to understand what an infection is before you learn about the things that might put a person at a higher risk for getting one. An infection occurs when germs enter a person’s body and multiply, causing illness, organ and tissue damage, or disease.

It’s also important for you to know that an infection can lead to a potentially life-threatening complication called sepsis. It’s very important to call your doctor immediately if you get an infection or develop any other signs or symptoms of an infection.

Some common germs and infections include the following:

Bacteria: Very small microorganisms. Some types of bacteria enter the human body from the air, water, soil, or food, and can cause infections and disease. Common bacterial infections include pneumonia, bronchitis, and ear infections.

Virus: A very simple microorganism that may cause illness or disease. Viral infections are passed on from other people. Common viral infections include the common cold, herpes, and flu.

Your immune system helps your body protect against these germs. Cancer and chemotherapy can damage this system, reducing your number of infection-fighting white blood cells and making it harder for your body to fight infection from germs.

Types of infections

Cancer and cancer treatments can make it more likely for you to get an infection. Find out more about how you could be affected.

Infections are caused by tiny living things (organisms) that get into the body and start multiplying. Some organisms are harmless and help our bodies to work properly. But others cause disease.

You might get an infection that makes you ill if these organisms get into your body and your immune system can't fight them off immediately. Some infections are life threatening, particularly if you have low resistance to infection from cancer treatment.

Some types of cancers and cancer treatment can weaken your immune system. They stop your bone marrow from making blood cells that help fight infection. This increases your risk of getting an infection.

The white blood cells play the biggest part in fighting infection. A low white blood cell count is called neutropenia (pronounced new-tro-peen-ee-a).

We’re all normally covered with bacteria that don’t do us any harm. But people with neutropenia are at risk. They can get infections from bacteria or viruses that normally live on their skin or inside their digestive system.

Infectious diseases

Infectious diseases are disorders caused by organisms — such as bacteria, viruses, fungi or parasites. Many organisms live in and on our bodies. They're normally harmless or even helpful, but under certain conditions, some organisms may cause disease.

Some infectious diseases can be passed from person to person. Some are transmitted by bites from insects or animals. And others are acquired by ingesting contaminated food or water or being exposed to organisms in the environment.

Signs and symptoms vary depending on the organism causing the infection, but often include fever and fatigue. Mild infections may respond to rest and home remedies, while some life-threatening infections may require hospitalization.

Many infectious diseases, such as measles and chickenpox, can be prevented by vaccines. Frequent and thorough hand-washing also helps protect you from most infectious diseases.

Infectious diseases Symptoms

Each infectious disease has its own specific signs and symptoms. General signs and symptoms common to a number of infectious diseases include:

Fever

Diarrhea

Fatigue

Muscle aches

Coughing

When to see a doctor

Seek medical attention if you:

Have been bitten by an animal

Are having trouble breathing

Have been coughing for more than a week

Have severe headache with fever

Experience a rash or swelling

Have unexplained or prolonged fever

Have sudden vision problems

Infectious diseases Causes

Infectious diseases can be caused by:

Bacteria:-- These one-cell organisms are responsible for illnesses such as strep throat, urinary tract infections and tuberculosis.

Viruses:-- Even smaller than bacteria, viruses cause a multitude of diseases — ranging from the common cold to AIDS.

Fungi:-- Many skin diseases, such as ringworm and athlete's foot, are caused by fungi. Other types of fungi can infect your lungs or nervous system.

Parasites:-- Malaria is caused by a tiny parasite that is transmitted by a mosquito bite. Other parasites may be transmitted to humans from animal feces.

Direct contact

An easy way to catch most infectious diseases is by coming in contact with a person or animal who has the infection. Three ways infectious diseases can be spread through direct contact are:

Person to person:-- A common way for infectious diseases to spread is through the direct transfer of bacteria, viruses or other germs from one person to another. This can occur when an individual with the bacterium or virus touches, kisses, or coughs or sneezes on someone who isn't infected.

These germs can also spread through the exchange of body fluids from sexual contact. The person who passes the germ may have no symptoms of the disease, but may simply be a carrier.

Animal to person:-- Being bitten or scratched by an infected animal — even a pet — can make you sick and, in extreme circumstances, can be fatal. Handling animal waste can be hazardous, too. For example, you can acquire a toxoplasmosis infection by scooping your cat's litter box.

Mother to unborn child:-- A pregnant woman may pass germs that cause infectious diseases to her unborn baby. Some germs can pass through the placenta. Germs in the vagina can be transmitted to the baby during birth.

Indirect contact

Disease-causing organisms also can be passed by indirect contact. Many germs can linger on an inanimate object, such as a tabletop, doorknob or faucet handle.

When you touch a doorknob handled by someone ill with the flu or a cold, for example, you can pick up the germs he or she left behind. If you then touch your eyes, mouth or nose before washing your hands, you may become infected.

Insect bites

Some germs rely on insect carriers — such as mosquitoes, fleas, lice or ticks — to move from host to host. These carriers are known as vectors. Mosquitoes can carry the malaria parasite or West Nile virus, and deer ticks may carry the bacterium that causes Lyme disease.

Food contamination

Another way disease-causing germs can infect you is through contaminated food and water. This mechanism of transmission allows germs to be spread to many people through a single source. E. coli, for example, is a bacterium present in or on certain foods — such as undercooked hamburger or unpasteurized fruit juice.

Infectious diseases Risk factors

While anyone can catch infectious diseases, you may be more likely to get sick if your immune system isn't working properly. This may occur if:

You're taking steroids or other medications that suppress your immune system, such as anti-rejection drugs for a transplanted organ

You have HIV or AIDS

You have certain types of cancer or other disorders that affect your immune system

In addition, certain other medical conditions may predispose you to infection, including implanted medical devices, malnutrition and extremes of age, among others.

Complications

Most infectious diseases have only minor complications. But some infections — such as pneumonia, AIDS and meningitis — can become life-threatening. A few types of infections have been linked to a long-term increased risk of cancer:

Human papillomavirus is linked to cervical cancer

Helicobacter pylori is linked to stomach cancer and peptic ulcers

Hepatitis B and C have been linked to liver cancer

In addition, some infectious diseases may become silent, only to appear again in the future — sometimes even decades later. For example, someone who's had a chickenpox infection may develop shingles much later in life.

Prevention

Infectious agents can enter your body through:

Skin contact or injuries

Inhalation of airborne germs

Ingestion of contaminated food or water

Tick or mosquito bites

Sexual contact

Follow these tips to decrease your risk of infecting yourself or others:

Wash your hands. This is especially important before and after preparing food, before eating, and after using the toilet. And try not to touch your eyes, nose or mouth with your hands, as that's a common way germs enter the body.

Get vaccinated. Immunization can drastically reduce your chances of contracting many diseases. Make sure to keep up to date on your recommended vaccinations, as well as your children's.

Stay home when ill. Don't go to work if you are vomiting, have diarrhea or have a fever. Don't send your child to school if he or she has these signs and symptoms, either.

Prepare food safely. Keep counters and other kitchen surfaces clean when preparing meals. Cook foods to the proper temperature using a food thermometer to check for doneness. For ground meats, that means at least 160 F (71 C); for poultry, 165 F (74 C); and for most other meat, at least 145 F (63 C).

In addition, promptly refrigerate leftovers — don't let cooked foods remain at room temperature for extended periods of time.

Practice safe sex. Always use condoms if you or your partner has a history of sexually transmitted infections or high-risk behavior.

Don't share personal items. Use your own toothbrush, comb and razor. Avoid sharing drinking glasses or dining utensils.

Travel wisely. If you're traveling out of the country, talk to your doctor about any special vaccinations — such as yellow fever, cholera, hepatitis A or B, or typhoid fever — you may need.

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