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Infection during or after treatment

Having cancer or treatment for cancer can weaken your immune system. This makes it more likely that you will pick up an infection and develop a fever.


What chemotherapy is

Chemotherapy means drug treatment. In cancer treatment, the term chemotherapy means treatment with cell killing (cytotoxic) drugs. Chemotherapy affects production of white blood cells in the bone marrow. Normally white blood cells help fight off infection.

Chemotherapy and infection

After chemotherapy, if your white blood cells are low, you are more likely to get infections. Any infection can also worsen more quickly. A trivial infection could become life threatening within hours if it isn’t treated.

Your chemotherapy nurse will tell you about the symptoms of infection to look out for, and when you need to call the doctor or go back to the hospital.

Not all chemotherapy drugs affect your bone marrow and increase the risk of infection. But many do. It depends on:

  • which drug you have
  • the dose of the drug – the higher the dose the more likely it is to affect your bone marrow
  • your age – chemotherapy is more likely to affect your bone marrow function if you are elderly
  • your general health
  • the type and stage of your cancer

When you are most at risk

These effects on your bone marrow usually begin around 7 to 10 days after each treatment and return to normal between 21 and 28 days.

When your white blood cell count is at its lowest you can feel very tired (fatigued). Some people also say they feel depressed. This can be really hard to deal with and make you wonder if you really want to go on with your treatment.

Things should improve and you will start to feel better again before your next treatment, as your blood counts rise. Unfortunately, they'll go down again after each treatment. But once your treatment is finished your blood cell counts will remain at normal levels.

To make sure your bone marrow is working well you will have regular blood tests. Sometimes your doctor may give you a course of antibiotics during your chemotherapy to help fight off an infection or stop you getting one.


What radiotherapy is

Radiotherapy uses high energy rays to treat cancer. Radiotherapy destroys the cancer cells in the treated area. Normal cells are also affected by radiation, if they are in the treated area.  

Radiotherapy and infection

Radiation can also affect the cells in your bone marrow, which produce your blood cells, including the white blood cells that normally fight off infection. But generally, radiotherapy only affects the area being treated and is less likely to affect your white blood cells than chemotherapy.

Who is most at risk

Treatment to a large area of your body, or treatment to the bones of the legs, chest, abdomen or pelvis, will mean your bone marrow is more likely to be affected. People having total body irradiation before a bone marrow or stem cell transplant will be severely affected and will have low red cells, white cells and platelets.

You will have regular blood tests during your treatment to check the number of red and white blood cells in your blood. 


Infection is a possible side effect of any type of surgery. The risk of infection depends on what type of surgery you have.

You might have antibiotics to reduce the chance of getting an infection after your operation. After an operation, you may have drainage tubes in place to stop fluid from collecting around the operation site. This is important because, as well as being uncomfortable or painful, fluid that does not drain away can be a site of infection.

Surgery does not weaken your resistance to infection nearly as much as chemotherapy or a bone marrow or stem cell transplant.

Targeted cancer drugs

Targeted cancer drugs (sometimes called biological therapies) can be used to stimulate the immune system to control the growth of cancer cells. 

Immunotherapy is a targeted treatment that uses substances normally involved in fighting infection. These substances are called cytokines. When you get an infection the body produces cytokines. They are responsible for some of the symptoms of infection, including fever.

As treatments, you have cytokines in much larger quantities than your body would normally produce. This seems to be the reason why flu like symptoms, including fever, can be a side effect of some targeted cancer treatments. 

Bone marrow and stem cell transplants

What transplants are

Bone marrow or stem cell transplants are ways of trying to cure some types of cancer. You have very high dose chemotherapy, sometimes with radiotherapy, to try to kill off the cancer cells. The high doses damage your bone marrow, so you need a bone marrow or stem cell infusion to replace the bone marrow cells you’ve lost.

Transplants and infection

You will have a low white blood cell count for quite a while after these types of treatments. This means you are more at risk of getting an infection. This is most likely to be from the normally harmless bacteria we all have in our digestive systems and on our skin. 

Graft versus host disease (GvHD)

There is a transplant side effect called graft versus host disease (GvHD) that some people get when they have marrow or stem cells donated by somebody else. GvHD can range from being mild to very serious. Although it is not an infection, it often causes a fever. Treatments for GvHD, such as steroids and drugs which affect your immune system, can increase your risk of getting an infection.

Last reviewed: 
22 Jun 2017
  • Cancer and its management (7th edition)
    J Tobias and D Hochhauser 
    Wiley-Blackwell, 2015

  • Neutropenic sepsis: prevention and management of neutropenic sepsis in cancer patients

    National Institute of Health and Care Excellence (NICE), September 2012

  • Oxford Textbook of Medicine (5th Edition)
    DA Warrell DA, TM Cox, JD Firth and  ER Benz Jr
    Oxford University Press, 2010

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