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People with cancer can be at risk for different types of infections. These infections differ in their risk factors, the symptoms they cause, how they are treated, and the chance of curing the infection. If you have an infection, your doctor will need to assess you to find out:
Your signs and symptoms (for instance, where you have pain, redness, and/or swelling) help your doctor know what tests are needed to find the cause of the infection. The results of certain tests (such as x-rays, CT scans, or lab tests done on body fluids) help pinpoint where the infection is and the type of germ causing it.
Common sites of infection in people with cancer include:
Germs can be bacteria, viruses, fungi, parasites and other organisms. Many kinds of germs normally live on the skin, in the intestines, or in the environment. These germs usually do not cause problems in people with normal defenses and healthy immune systems. But if the normal defense barriers and immune system are weak, the germs can get in the body, grow, and cause damage.
These infections are often called opportunistic infections, because the germs use the opportunity of a patient’s weakened defenses to cause illness.
Knowing the exact type of germ that’s causing an infection helps doctors choose the best treatment. Different drugs are used to treat each of the main types of germs – bacteria, viruses, fungi, and parasites. And even among the main types of germs, different types are treated with different drugs. This means an antibiotic that can kill one type of germ might have no effect on another type of germ. And some germs become resistant to certain antibiotics so sometimes more than one type of treatment is needed to kill the germ that's causing an infection.
Lab tests identify what germs may be causing your infection. Some lab tests can also tell your doctor what medication your infection will best respond to. If you have symptoms that point to a certain area of infection, samples will be taken to check for germs in that area. For example, sputum samples may be taken if you have a cough or are short of breath.
Urine samples may be taken if you have blood in your urine or feel pain while passing urine. Sometimes, if a person has a very low white blood cell count and a fever, blood and urine samples will be taken before other symptoms start. Your health care team will let you know what lab tests you may need and what samples will need to be collected.
Your doctor may use different tests for different kinds of germs. You may hear your cancer care team mention a gram stain test, viral antigen tests to test for viruses, or genetic tests that test for certain germs by testing their genetic make-up. A common test used in patients who have very low white blood cell count (neutropenia) and fever is a culture and sensitivity test. The culture is done first, followed by the sensitivity test. For the culture, samples from the suspected site of infection are collected and put in the lab to grow. Sometimes, bacteria, and fungi may take at least a few days before they can be seen. Viruses may take a few weeks to grow. Once enough germs have grown, they are tested and identified. After bacteria or fungi has been cultured, a sensitivity test may be done on the cultured sample. This will help show the best medication to kill the germ causing a certain infection
Because infections in people with cancer can quickly get worse, sometimes treatment is started before the lab results come back. Often broad-spectrum antibiotics are started right away. A broad-spectrum antibiotic will treat different bacteria at the same time. Treatment may be changed after the lab tests have identified the exact germ and which drug will work best to treat it. Doctors know which germs tend to infect certain body parts of people with cancer. So they can often make an educated guess at which germs are most likely causing a patient’s infection. Educated guesses are very important because it can take many days to get the results of tests that show the exact type of germ causing an infection and which drug will best stop or kill it.
Infections in cancer patients are often treated according to the germ that is causing them. Anti-infectives are drugs used to prevent or treat infections, for example:
Anti-infectives are often given to patients when an infection is suspected or after an infection has been identified to treat the infection. Other times, they may be given to patients who have known risk for a particular germ before they get an infection to prevent the infection.
For patients with a suspected infection; after a physical exam, lab tests, cultures, and sometimes even imaging studies or special procedures will be done. This will help the doctor find out exactly where the infection is and help figure out which germ may be causing it. Then anti-infectives (which can be antibiotics, anti-viral, anti-fungal, or anti-protozoal drugs) are started quickly. After the exact germ is identified, the same anti-infective may be continued, or new ones may be started if the tests show others would work better or if another type of germ is identified.
Only bacterial infections are described below. If you have a different kind of infection, talk to your doctor for more information about it and its treatment.
When treating bacterial infections in people with weak immune systems, an antibiotic that will treat many different bacteria are often chosen first, especially if doctors aren’t yet sure what’s causing the infection. These are called broad-spectrum antibiotics. Often, more than one antibiotic is used at the same time.
Drug-resistant germs: Even in serious situations, overuse of antibiotics must be avoided because this can make some bacteria resistant to these drugs. Such germs are called drug resistant because they no longer respond to the antibiotics that killed them in the past. Germs change and adapt all the time. For example, some strains of Staphylococcus (staph) have become resistant to certain antibiotics. These strains get special names. Staph that’s resistant to methicillin is called methicillin-resistant staph aureus, or multi-drug-resistant staph aureus. This is often shortened to the initials MRSA. There are newer drugs that can still work against some of these hard-to-kill germs. To avoid spreading drug-resistant bacteria to other patients, health care workers often wear disposable gowns and gloves when caring for people known to have these infections.
Fever, swelling, pain, and other signs of infection in a person known to have a weak immune system are treated as medical emergencies. In the past, people with cancer were almost always put in the hospital to treat infections, and some still are. But many patients can take their antibiotics at home as pills or liquids. Those who need intravenous (IV) antibiotics may be able to get them in infusion clinics, doctor’s offices, or even at home. If this happens, talk to your cancer care team to learn where you can receive treatment.
For the first few days, patients should be assessed daily to see if the infection is getting better and to see if they are having any side effects. The doctor might also want you to have lab tests often during treatment. If the patient still has a fever during treatment, they should be assessed daily by their cancer care team. Anti-infectives may be changed or new ones may be started when the final culture or other test results come in. The culture results should tell the doctor which germ is causing the infection.
If the patient doesn’t get better, an infectious disease specialist may be called in. These are doctors who specialize in treating infections. This doctor may recommend extra testing and different treatments.
In some cases, injections of drugs called CSFs (colony-stimulating factors) may be given to stimulate the bone marrow to produce more white blood cells (WBC) so the body can better fight the infection. Examples of CSFs include filgrastim (Neupogen), tbo-filgrastim (Granix), and pegfilgrastim (Neulasta).
Each type of infection is treated with different drugs and for different lengths of time. If you have any questions about the drugs you are given or why you’re taking them, talk with your doctor or nurse.
The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
Freifeld AG, Kaul DR. Infection in the patient with cancer. In Niederhuber JE, Armitage JO, Kastan MB, Doroshow JH, Tepper JE, eds. Abeloff’s Clinical Oncology. 6th ed. Philadelphia, PA: Elsevier; 2020:544-562.
National Comprehensive Cancer Network (NCCN). Prevention and treatment of cancer-related infections. 2018. Version 1.2019. Accessed at https://www.nccn.org/professionals/physician_gls/PDF/infections.pdf on August 27, 2019.
Palmore TN, Parta M, Cuellar-Rodriguez J, Gea-Banacloche JC. Infections in the cancer patient. In DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2019:2037-2068.
Last Revised: February 1, 2020
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