Having treatment for cancer can increase your risk of picking up an infection. Here we explain why and which infections are most common.

Why cancer treatment increases infection risk

Chemotherapy and radiotherapy work in a similar way, in that they both kill cells that are dividing. Cancer cells divide very often, which is why they are most sensitive to the treatment. But the cells of some healthy body tissues divide frequently too, including the bone marrow. This is where all your blood cells are made. The job of white blood cells is to fight infection. So the more your white blood cell count falls, the greater the risk of you getting an infection.

Infection and types of cancer treatment

Chemotherapy is the cancer treatment most likely to increase risk of infection. Not all chemotherapy drugs carry the same risk. Some affect the bone marrow more than others. The amount of treatment is important too. If you have high dose chemotherapy, you may need to spend some time in isolation while your blood counts are very low.

Radiotherapy can also affect your blood counts, but this is less common. It depends on the treatment you’re having. Total body irradiation (which you have with a bone marrow or stem cell transplant)  is most likely to cause a severe drop in blood cell count. Your white cells may also be affected if you have a large area treated with radiotherapy, particularly if that includes the large, flat bones (the hips and pelvis, breastbone, shoulder blades) where most blood cells are made in adults.

If you have combined radiotherapy and chemotherapy, your blood cell counts may be affected even more.

Some targeted cancer drugs (sometimes called biological therapies) and immunotherapies can affect your blood counts. Immunotherapies include interferon and interleukin. They use the immune system to fight the cancer, but this can mean that you are more at risk of infection while you’re being treated. 

Rituximab is a targeted therapy - a drug called a monoclonal antibody. It targets a protein on the surface of leukaemia and lymphoma cells. If you have long term maintenance treatment, it can cause a drop in proteins made by some white blood cells that fight infection (gamma globulins) and increase your infection risk.

Other cancer treatments such as hormone therapies won’t increase your infection risk.

What infections are most common?

When your resistance is low, you can more easily develop an infection from bugs that you’d normally fight off. If your white cell count is very low (you are neutropenic), you can even develop an infection from germs that we all normally carry around on our skin, or in our gut.

You may be at increased risk of bacterial, fungal or viral infections. Common bacterial infections include staphylococci and streptococci, which are both found on the skin and can cause wound, skin or throat infections. Or clostridium which lives in the digestive system and can cause severe diarrhoea. Other common gut infections include listeria and E coli.

Thrush is a very common fungal infection. People having chemo, frequently get a thrush infection in the mouth. You’ll notice white patches and red sore areas. Your doctor may give you a mouthwash to try and prevent thrush. Another fungal infection that affects people on chemo is aspergillus. This is all around us and doesn’t cause any problems normally, but if your resistance is low, it can cause a lung infection.

Cold and flu are the most common viruses around. After cancer treatment, you may also be at risk of cold sores (from the herpes virus). If you’ve had chicken pox in the past, it can become reactivated causing shingles. Another virus a lot of us will have had and may carry is called CMV. This can cause severe chest infections in people who’ve had high dose treatment.

What you can do if you’re at increased risk of infection

Your nurse or doctor will talk to you about ways of reducing your risk, but here is a list of tips that may help.

  • Don’t go near anyone who has a cold, sore throat, stomach bug or any other sign of obvious infection
  • Avoid busy, crowded places - public transport in the rush hour, crowded shopping centres, pubs and clubs
  • Shower every day. Use separate towels.
  • Wash your hands - often! After going to the loo (obviously…), before preparing food or eating, after touching animals and when you get home after being out. Soap and hot water are best (better than commercial hand gels).
  • Do your mouthcare properly and regularly – as your doctor or nurse has advised
  • Don’t go swimming. If you go to a gym or sports centre, choose a less busy time

Food hygiene is also important.

  • If you are neutropenic, don’t eat soft cheese, soft or uncooked eggs (no homemade mayo), pate, prepacked sliced meats, smoked fish or sandwiches, cook-chill meals
  • Store food properly – at the right temperature, and with uncooked and cooked foods separate in the fridge
  • Don’t reheat cooked food. Make sure your food is thoroughly cooked (no rare meat for instance)
  • Wash fruit and salad veg thoroughly or avoid salad if you’re neutropenic. Peeling fruit before eating it is also more hygienic