Types of infections

Cancer and cancer treatments can make it more likely for you to get an infection.

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.

Causes of infection

Bacteria are the most common cause of infections in people with cancer. Types of bacteria that cause infection are explained below:


Staphylococcal infections (often shortened to Staph) mainly affect the skin. Two common types are Staphylococcus epidermis and Staphylococcus aureus.

They usually cause mild infections, but these can be more serious in people with cancer. MRSA is a type of Staph aureus infection that standard antibiotics can’t treat. MRSA stands for Methicillin Resistant Staphylococcus Aureus. 

Staphylococcus epidermis bacteria are commonly found around central lines such as a PICC line. 


Streptococci (often shortened to Strep) are common bacteria that can cause tonsillitis and skin infection (cellulitis). They are usually treated with antibiotics like penicillin. Pneumococcal pneumonia is a chest infection caused by a type of strep, especially in people who have had their spleen removed.

Streptococcus bacteria are commonly found around central lines such as a PICC line. 

Another type of bacteria that can affect people with cancer are Enterococci. These can cause bladder infections and blood poisoning (septicaemia).


Pseudomonas infections are rarer, but can be a problem for people who have weak immune systems or who are in hospital for some time. The germs live in soil, water and on the skin.

Clostridium difficile

Clostridium difficile (C. diff) infection is most common in people who are already on antibiotics. Certain bacteria can live normally in the bowel in just the right numbers to keep it healthy. But being on antibiotics can upset the balance and allow some bacteria to multiply and become harmful.

Symptoms include diarrhoea, abdominal pain and fever.

Escherichia coli

Escherichia coli (E. coli) infections also affect the gut causing tummy (abdominal) pain, diarrhoea and fever.

Listeria monocytogenes

Listeria monocytogenes is commonly known as Listeria. The infection is caused by eating contaminated food. It is rare, but can be serious if you have a weak immune system.

People with cancer may have an increased risk of developing the illness. You can reduce your risk by avoiding certain foods, including:

  • pre packed and sliced delicatessen meat
  • soft cheeses or paté
  • smoked fish
  • pre prepared cooked chilled meals
  • pre prepared sandwiches
  • unpasteurised milk

Viruses are tiny particles that can't live on their own. To reproduce, they need to infect a living cell, such as a cell in a human body.

It's a virus that causes flu. The most common types of viruses that cause infections in people with cancer include some of the following.

Common cold viruses

Common cold viruses occur often in healthy people and do not usually cause major problems. But these viruses can cause serious infections, such as pneumonia, if your immune system is weak. You should try to stay away from people with colds if you're having cancer treatment that weakens your immune system, though this might seem difficult.

Herpes simplex

Herpes simplex is a virus that causes cold sores and genital herpes.

These infections are usually mild when you have a healthy immune system. But the virus can cause serious infections for people with a weakened immune systems, including some people with cancer.

Varicella zoster

Varicella zoster is related to the herpes simplex virus. Varicella zoster is the same virus that causes chicken pox. It can cause very serious and sometimes fatal infections, such as pneumonia, in people with cancer.

The virus also causes a painful condition called shingles. You can only get shingles if you have had chicken pox in the past. This is because after you've had chicken pox the virus does not fully go away. It lies inactive in the body, but can become active again if the immune system is weak.

This is why people can get shingles after chemotherapy treatment.

Cytomegalovirus (CMV)

Cytomegalovirus (CMV) is common and can cause several types of infections.

Cytomegalo just means large cell, which is how the infected cells look under a microscope (swollen and big). Most people will have had a CMV infection by the time they are adults.

It isn’t generally serious. But the virus can remain inactive in your body for many years and cause recurrent infections.

This usually only becomes a problem in people who have very weakened immune systems. For example, it can cause serious chest infections after a stem cell or bone marrow transplant.

Flu (influenza)

Flu is an infection caused by viruses. It's very infectious. You mainly catch it from coughs and sneezes of people who have a flu virus.

When you have flu you feel unwell more quickly than with a cold. Flu often causes:

  • high temperatures (fever)
  • aching muscles
  • coughing
  • headaches

Many cancer treatments can affect the immune system, so you're less able to fight infections. It will take you longer to recover from flu if you do get it. And you're more likely to develop complications such as chest infections.

Your doctor might suggest you have the flu jab and will tell you how and when to get it.

Fungi can live in our bodies without causing any problems. But it can cause problems if a fungal infection occurs when your immune system is weak.

The most common fungal infection in people with cancer is Candida (thrush). You're more at risk from thrush if you have a sore mouth from chemotherapy or radiotherapy treatment. Chlorhexidine mouthwashes can help to prevent thrush in the mouth. You may notice white patches with red and sore skin underneath. 

Thrush can be treated with:

  • a liquid anti fungal drug called nystatin
  • miconazole gel or cream
  • fluconozole

If your first or second treatment doesn't work, you might have swabs to see which treatment the thrush is sensitive to. 

Women can also get vaginal thrush, which is treated with anti fungal creams or pessaries.

Less common fungal infections include:

  • aspergillosis
  • pneumocystis

Aspergillus can cause a serious chest infection that needs treatment with anti-fungal drugs through a drip.

The pneumocystis bug can cause a serious form of pneumonia called PCP. This stands for pneumocystis carinii pneumonia. You might take co-trimoxazole (Septrin) to help prevent or treat it.

Protozoa are the smallest animals known to man. Toxoplasmosis is an infection caused by protozoa. It causes a mild illness in healthy people, but those with severely weakened immune systems can get serious infections that spread to the brain.

Remember many of these infections are only a problem if your resistance to infection is very low. Talk with your doctor or specialist nurse if you are worried about your risk of getting infections.
Last reviewed: 
02 Aug 2019
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  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. If you need additional references for this information please contact patientinformation@cancer.org.uk with details of the particular risk or cause you are interested in. 

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