Infection is when harmful organisms, such as bacteria or viruses, enter the body and the immune system cannot destroy them. The immune system is the body’s natural defence against infection and disease. The body’s other natural defence systems, such as the skin, also help protect you against infections.

Infections are common in people receiving cancer treatment because it lowers the number of white blood cells (WBCs). WBCs are an important part of the immune system and play a key role in defending the body against viruses and bacteria.

There is a greater risk of infection when WBCs, especially neutrophils, are lowered. Neutrophils are a type of WBC that surround and destroy bacteria. People receiving cancer treatment are most vulnerable to infection at a certain time in the treatment cycle when the number of neutrophils is very low. A low neutrophil count is called neutropenia. Not everyone receiving cancer treatment will have neutropenia, but many do. Neutropenia develops if too many neutrophils are destroyed before the bone marrow can replace them. Neutropenia usually occurs 10–14 days after receiving chemotherapy.

Once the WBC count drops, it remains low for a week or more. The low point in blood cell counts when the body’s resistance to infection is weakest is called the nadir. During nadir, it is important to do everything possible to lessen the chances of infection and to seek immediate treatment if an infection is suspected.

Infection can be very serious for people with cancer. Developing an infection can mean a hospital stay, delays in treatment, serious complications and additional care. Pneumonia and chicken pox are 2 serious infections for people receiving cancer treatment. Infection is more common in children with cancer.


Infection can have many different causes, including the following.

Certain types of cancer

Some cancers, such as leukemia, multiple myeloma and lymphoma, start in cells of the immune system. They can affect the bone marrow so it can’t make enough healthy WBCs. Cancer that spreads, or metastasizes, to the bone and bone marrow can lower the level of white blood cells, red blood cells and platelets in the blood. Examples of cancers that spread to the bone and bone marrow include breast and prostate cancer.

Surgery and medical procedures

Surgery and other medical procedures break the skin or mucous membrane, which can allow organisms to enter the body. Indwelling central venous catheters are tubes placed in a vein in the neck, groin or chest that remain in place for some time. They are used to give chemotherapy, blood products, intravenous fluids and medicines. They can also provide a way for harmful organisms to get into the body. Urinary catheters or feeding tubes can also allow harmful organisms to enter the body.

Surgery to remove the spleen is called splenectomy. It is used to treat certain types of cancer. It may also lower resistance to infection because the spleen is an important part of the immune system.


Chemotherapy can cause bone marrow suppression. Bone marrow suppression is a condition in which the bone marrow doesn’t make enough healthy blood cells, including WBCs. Some chemotherapy drugs have a greater effect on the bone marrow and immune system than others.

Radiation therapy

Radiation therapy can affect the bone marrow and lower WBC counts. This is especially true if an area that contains a large amount of bone marrow, such as the pelvic bones, is treated with radiation. Treating a large part of the skeleton with radiation, such as total body irradiation, can also affect the bone marrow. Radiation therapy is also more likely to affect the bone marrow if you receive chemotherapy at the same time as radiation therapy.

Stem cell transplant

A stem cell transplant uses high-dose chemotherapy, radiation therapy or both to kill cancer cells and destroy bone marrow cells to make room for new stem cells. A stem cell transplant lowers the WBC count for a while before new blood cells start to grow.

An allogeneic stem cell transplant uses stem cells from a donor. People who receive an allogeneic stem cell transplant can develop a condition called graft-versus-host disease (GVHD). They may be given drugs that suppress the immune system to prevent and treat GVHD. These drugs also increase the risk of developing infections.


Corticosteroids are drugs that act as an anti-inflammatory by reducing swelling and lowering the body’s immune response. They may be used as part of cancer treatment or to help reduce pain and swelling associated with cancer. These drugs can suppress the immune system and may also hide the signs and symptoms of an infection.

General health

Cancer or its treatment can sometimes lead to poor nutrition. They can also cause lack of sleep, stress, poor diet and other side effects. These effects on your health may weaken the immune system and increase the risk of infection.


Your doctor will try to find the cause of infection. This may include asking about your medical history and doing a physical exam to look for any signs of infection.

You may also need to have the following tests:

  • blood tests, such as a complete blood count (CBC) or blood cultures
  • urinalysis or urine cultures to check for a urinary tract infection
  • cultures of mouth sores, skin or wound sores, intravenous sites or vascular access devices to check if these are sources of infection
  • chest x-ray or a sample of sputum to check for pneumonia
  • stool samples, if you have diarrhea, to check for infection in the gastrointestinal tract
  • other imaging tests to check for pockets of infection or abscesses

A CBC checks the levels of the different types of blood cells. Higher numbers of white blood cells (WBCs) may indicate an infection. For people on chemotherapy, the WBC count may be low and may not show when an infection is present. Blood cultures may be done to check if an organism is causing an infection in the blood.

Cultures are done to identify the organism causing the infection. Samples from the site of infection are put on a special gel or in a broth to see which organisms grow. Sensitivity testing involves using samples of different antibiotics on the organisms to help identify which antibiotic would work best. Together, these tests are called culture and sensitivity (C&S).

Gram stain tests involve taking samples from the suspected site of infection. These samples are treated with certain stains, or dyes, that make the bacteria easier to see. Then they are looked at under a microscope. Gram stains can provide information about the type of organism. It may take 24–48 hours until test results are available.

Types of infection

An infection can be caused by many types of micro-organisms, such as bacteria, viruses, fungi or protozoa. Some of these micro-organisms normally live on the skin, in the mouth or in the intestines. These micro-organisms do not usually cause a problem in people with a normal immune system. But when the immune system is not working as well because of cancer or its treatments, these micro-organisms are given the opportunity to multiply. These are called opportunistic infections and they can be serious.

Bacterial infections

Bacteria are the most common type of infection-causing organism in people with cancer. Many bacteria live on and in our bodies. They are called normal flora. These bacteria do not usually cause infection. But they may cause problems, including serious infection, when the white blood cell counts are low and the immune system is weak.

Viral infections

Viruses cause infections, such as the common cold. Certain viruses can cause serious infections in people with very low WBC counts. Viruses are hard to identify and cannot be treated with antibiotics.

Fungal infections

Fungi can pose a problem for people with weakened immune systems. The most common fungal infection in people with cancer is thrush. Thrush is an infection of the mouth caused by the fungus Candida. Candida can also grow in a woman’s vagina and cause vaginal thrush, or a yeast infection.

Protozoan infections

Protozoa can cause serious infections in people with weakened immune systems due to an organ transplant, cancer or other immune-suppressing illnesses. Toxoplasmosis is a serious protozoan infection that can damage the brain or heart.

Sites of infection

Infections can occur almost anywhere in the body. The most common places for an infection are the:

  • skin
  • mucous membranes
  • respiratory system, such as the sinuses or lungs
  • blood
  • urinary system, such as the bladder or kidneys
  • gastrointestinal (GI) tract, such as the mouth, stomach or intestines
  • nervous system, such as the brain or spinal cord

Bacteria, viruses or fungi can cause skin infections. They can also cause a serious infection of the respiratory tract called pneumonia.

Cancer treatments can cause changes in the mucous membranes of the GI tract that can lead to infections. They can also serve as an entry point for micro-organisms living in the GI tract to invade the body. Mouth sores can become infected with yeast or herpes simplex virus. People with cancer also have a higher risk of abdominal infections with bacteria, such as Clostridium difficile(C. difficile).


Symptoms of infection can vary. Having a fever, which is a temperature over 38oC, is the most common sign of infection. But some people with an infection may not have a fever.

Other symptoms of infection include:

  • chills or shivering
  • unusual sweating
  • mouth sores or thick white patches inside the mouth
  • blisters on the lips or skin
  • redness, heat, swelling or discomfort from a wound, surgical cut (incision) or area around an intravenous line or vascular access device site
  • sore throat
  • cough, which may produce phlegm
  • shortness of breath or rapid breathing
  • frequent, painful urination
  • diarrhea
  • abdominal pain
  • vomiting
  • unusual vaginal discharge or itching
  • dizziness or light-headedness
  • increased sleepiness
  • irritability
  • weakness, including being too tired to eat, drink or perform normal activities
  • sinus pain or pressure
  • earaches, headache or stiff neck

Preventing infection

An antibiotic is a drug that fights bacterial infections. Antiviral drugs fight viruses and antifungal drugs fight fungi. These drugs may be ordered if the white blood cell (WBC) count becomes too low and the healthcare team feels there is a high risk that an infection will develop. Giving drugs to prevent an infection is called prophylaxis. Antibiotics and other infection-fighting drugs may be given by mouth (orally) or by intravenous.

In some cases, colony-stimulating factors (CSFs) may be ordered. These drugs stimulate the bone marrow to make more blood cells.

You can take the following steps to help lower your risk of getting an infection.

Practise good personal hygiene

This is one of the most effective ways of avoiding infection. Wash your hands frequently with soap and water. Carry a bottle of hand sanitizer in case a sink isn’t available to wash your hands. Always wash your hands when preparing food. Family members should always wash their hands when returning home from school, shopping or work.

Have a shower, sponge bath or bath everyday to lower the amount of bacteria on the skin. Use an electric shaver instead of a razor when shaving to prevent breaks or cuts in the skin.

Keep a close watch on the mouth, anal area, biopsy and surgery sites, and areas of injury, such as cuts in the skin (especially on the fingers and toes), to monitor for any signs of infection. Clean the anal area gently but thoroughly after each bowel movement.

Avoid contact with stool and urine from pets and other animals. It is fine to play with a pet, but people with cancer should not groom the pet, empty litter boxes or clean pet cages.

Protect your skin

Protect your skin from cuts and scrapes. Wash any cuts right away with soap and water and keep them clean. Apply a bandage to cuts and scrapes for the first few days to keep them clean.

Protect the hands and feet from cuts and injury. Wear gloves if working in the garden or with dirt as garden soil and plants often contain bacteria. Always wear shoes or slippers to prevent cuts and bruises. Do not cut, bite or tear the cuticles of the fingers or toe nails. Use lotions and moisturizers on the skin to prevent drying, chapping and cracking.

Do not squeeze or scratch pimples. Use sunscreen, wear a hat or scarf, and find shady areas to avoid sunburn. Do not play or swim in ponds, lakes or rivers.

Maintain good general health

Whenever possible, get enough rest, eat a well-balanced diet, drink plenty of fluids and get regular exercise.

If you have low blood cell counts, take steps to protect yourself. Avoid anyone with signs or symptoms of an infection, such as fever, cough, sneezes, sore throat or rash. Avoid large indoor crowds. If necessary, stay home from school or work. Do not schedule dental procedures or teeth cleaning. Let the healthcare team know if there has been contact with anyone suspected of having or diagnosed with chicken pox, measles or mumps.

Practise food safety

Follow food safety guidelines to reduce the chance of contaminating food. Wash raw fruit and vegetables well before eating them. Do not eat raw or undercooked fish, seafood, meat, chicken or eggs because they may contain bacteria that can cause infection. Do not have food or drinks that are mouldy, spoiled or past the freshness date.

Do not share items such as spoons, forks, glasses, thermometers or toothbrushes. Wipe the tops of cans and jars clean before opening them to reduce the chance of contamination from bacteria.

If tap water is a concern (for example in homes that use well water), use bottled water while you are in treatment or consider purchasing a home faucet filter.

Practise good mouth care

Practise good mouth and dental hygiene 4 times a day. Use an extra-soft toothbrush that won’t hurt the gums. Replace toothbrushes every 3 months to reduce the chance of infection in the mouth. Get a new toothbrush after treating a mouth infection.

Check all surfaces of the mouth for sores each day. Your healthcare team may recommend using a mouthwash during chemotherapy to kill bacteria.

Plan dental checkups or dental procedures when blood cell counts are normal and there is less risk of infection. Visit the dentist regularly because care of the mouth and teeth is very important. Ask your dentist about using dental floss.

Use and care for medical devices properly

If you have a catheter, follow care instructions carefully and always wash your hands before handling the catheter.

Follow care instructions for venous access devices, such as a central venous catheter or peripherally inserted central catheter (PICC).

Avoid rectal thermometers, suppositories and enemas. These can add to the risk of infection by introducing bacteria through tiny tears in the anus or rectum. Avoid constipation because straining can also cause small tears in the anus.

Ask about vaccines

Talk to your healthcare team about immunizations, or vaccinations. Depending on the treatment given, there may be some vaccinations that should be avoided and others that should be given. In general, “killed” vaccines can safely be given. Examples of killed vaccines include those for the flu, pneumonia, hepatitis and tetanus. Some “live” vaccines, such as those for the measles or mumps, may not be safe.

Managing infection

You can get sick very quickly if you have an infection when your white blood cells are low, even if you still feel well. Infection accompanied by fever and neutropenia is called neutropenic fever. It is a medical emergency in people with cancer and it needs immediate attention and treatment. Infections can be life-threatening if they lead to a condition called septic shock.

If you are on chemotherapy, your healthcare team will usually advise you to go to your closest emergency department if you have a fever of 38oC.

Using antibiotics to manage infection

If you develop an infection while your WBC count is low, your doctor will order tests. These tests may include blood cultures to try to identify the organism causing the infection. Your doctor will usually start you on a broad-spectrum antibiotic before the test results are known because infections can spread quickly. Broad-spectrum antibiotics are directed against many organisms that could be causing the infection. Once the cause of the infection is identified, the antibiotic may be changed to one that is specifically used to treat a particular organism.

Your doctor will select an antibiotic based on your history, symptoms, allergies, recent antibiotic use and test results. For most infections, antibiotic treatment will continue for 7–14 days. Treatment depends on the organism causing the infection, your overall health and how you respond to treatment. Different drugs are used to treat different types of organisms. These can be antibiotic, antiviral, antifungal or other drugs.

If the infection does not respond to treatment after 3–5 days, the healthcare team may decide to add more drugs or change the drugs.

Doctors try not to overuse antibiotics because some bacteria can become resistant to them. When this happens, the bacteria will not be killed by the same antibiotic that worked before. This is called antibiotic resistance.

Managing a fever

Fever over 38oC is the most common sign of an infection. A fever is the body’s way of protecting itself. When foreign substances, such as germs, enter the body, the body releases substances called cytokines to increase the temperature and make the immune system work better.

The surface air feels cooler as the body temperature increases, causing the body to shiver. Shivering occurs when the muscles contract to produce more heat. As the body temperature increases, it produces a fever. You can help lower a fever by taking acetaminophen (Tylenol) and helping the body get rid of heat. Preventing and correcting dehydration can also bring your fever down.

Acetaminophen will not treat what is causing the fever, but it will help lower the temperature and make you more comfortable. Do not take acetaminophen unless you doctor says it’s okay. Drugs can mask a fever, and it is important for the healthcare team to be aware of the fever and to treat the infection that is causing it.

Do not take acetylsalicylic acid (ASA, Aspirin, salicylate) or ibuprofen (Advil, Motrin) because these drugs promote bleeding, especially in the gastrointestinal tract. People receiving chemotherapy have a higher risk of bleeding. Take other medications prescribed for fever or infection only as ordered by your doctor.

To help keep cool, dress in light clothing that allows air to pass through to the skin and doesn’t trap body heat. Cover up with a light sheet and put a cool washcloth on the forehead for comfort. Drink cool fluids every hour to prevent dehydration. Change damp clothing and bed linens to prevent getting chilled.

Managing shaking chills

Shaking chills are also called rigors. They occur when the body shakes because it is cold. They are similar to shivering with an infection and fever, but are much more intense. You may get rigors from a very bad infection, from some drugs or sometimes during a blood transfusion.

Let the healthcare team know right away if you have shaking chills. Try to relax, breathe deeply and focus on the chills being gone. Keep warm with blankets, sweaters and hot water bottles. When the rigors stop, you may feel very hot. Use cool washcloths on your head and neck for comfort.

Expert review and references

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