Types of infection

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

Staphylococcus 

Staphylococcal infections (often called 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. 

Streptococcus 

Streptococci (often called strep) are common bacteria. They can cause tonsillitis and skin infections (cellulitis). They are usually treated with antibiotics like penicillin.

Pneumococcal pneumonia is a chest infection caused by a type of strep. People are at risk of developing this type of infection if they have a weakened immune system. Or have had their spleen removed.

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

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

Pseudomonas 

Pseudomonas infections are not as common. But they can be a problem for people who have a weak immune system. Or who are in hospital for some time. The bacteria live in soil, water, and on the skin.

Pseudomonas infections are resistant to some antibiotics. 

Clostridium difficile

Clostridium difficile is also called clostridioides difficile or C. diff. It is a common infection in people who are already on antibiotics. C. diff and other bacteria live normally in the bowel in just the right numbers to keep it healthy. But being on antibiotics can upset the balance and allow the C. diff bacteria to multiply and become harmful.

Symptoms include diarrhoea, loss of appetite tummy (abdominal) pain, and fever.

Escherichia coli 

Escherichia coli (E. coli) infections can also affect the gut. There are many E.coli strains. Some infections may be mild. But they can also be very serious requiring treatment in hospital. Symptoms include tummy 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.

The most common 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 problems. But these viruses can cause serious infections. For example, pneumonia if your immune system is weak. A cold can spread easily between people. You should try to stay away from people with colds if you're having cancer treatment that weakens your immune system. 

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 in people with a weakened immune system. This includes some people with cancer.

Varicella zoster

Varicella zoster is related to the herpes virus. Varicella zoster is the same virus that causes chickenpox. Having chickenpox could make you very unwell. Particularly if your immune system is weak due to your cancer treatment. Contact your healthcare team if you think you have been in contact with chickenpox. 

The virus also causes a painful condition called shingles. Shingles is an infection that affects the nerves and skin. The main symptoms are a rash and pain. 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.

Cytomegalovirus (CMV)

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

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. You mainly catch it from coughs and sneezes of people who have the flu virus. Viruses are always changing. So the flu virus this year will be slightly different to the one from last year. 

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

• high temperatures (fever)

• aching muscles

• coughing

• headaches

• a sore throat

Many cancer treatments can affect the immune system. So you're less able to fight infections. It will take you longer to recover from the 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 vaccine and will tell you how and when to get it.

Coronavirus (COVID-19)

COVID-19 is an infectious illness caused by a type of coronavirus. There are several types of coronaviruses. Some cause mild illnesses such as a cold, while others can be more serious and affect your breathing or respiratory system. For most people, the virus won't cause serious problems. But for some people, the virus can have severe complications.

Your doctor might suggest you have the COVID vaccine. They can 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.

A 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. Chlorhexidine mouthwashes can help to reduce the risk of thrush in the mouth. You may notice white patches with red and sore skin underneath. Thrush can also affect the penis and vagina.

Thrush is usually treated with antifungal medicine. 

Less common fungal infections include:

• aspergillosis

• pneumocystis 

Aspergillus can cause a serious chest infection that needs treatment with antifungal drugs through a drip.

Pneumocystis 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 very small living organisms that have one cell.

Toxoplasmosis is an infection caused by protozoa. It causes a mild illness in healthy people. But people with a weakened immune system can get serious infections. The infection can affect the brain.

Toxoplasmosis is often found in cat poo. It is important to take extra care if you handle cat litter.