This information is for people who have a reduced immunity due to the effects of cancer or its treatment. It is about how to avoid infection when your immunity is low.

The immune system is the body's defence against bacteria, viruses and other foreign organisms or harmful chemicals. It is very complex and it has to work properly to protect us from the harmful bacteria and other organisms in the environment which may infect our body.

There are three parts of the immune system:

• The skin and mucosal membranes
• Soluble proteins produced by the body, which are present in body fluids
• Specialised blood and lymph cells.

The skin and mucosal membranes

The skin and the lining of the body cavities that open to the outside, such as the gut and the reproductive tract, are protective barriers that prevent invasion by any harmful organisms.

The oil or 'sebum' produced by the skin keeps it slightly acidic, which controls the growth of any organisms on the skin. Cells in the lining of body cavities produce fluids, such as saliva in the digestive system and mucus in the lungs, which provide a defence against harmful organisms. The body has its own natural, helpful organisms, which also prevent other more dangerous organisms from taking over.

Proteins

Special proteins and chemicals are present in body secretions and fluids, and if organisms do manage to enter the body the proteins attack them in various ways, often by dissolving their protective outer layer.

Specialised blood and lymph cells

Specialised cells are produced by the bone marrow (the spongy cells in the middle of some of our bones) and the lymphatic system. The lymphatic system is a complex system made up of organs such as bone marrow, the thymus, the spleen and lymph nodes which are found throughout the body and which are connected by a network of tiny lymphatic vessels.

Many types of white blood cells play a part in killing invading organisms that manage to enter the body. They arrive at the site of damage or infection and destroy these organisms (known generally as 'antigens').

Cancer and its treatment can affect the immune system in a number of ways. Some cancers, particularly lymphomas and leukaemias, may reduce the effectiveness of the body's natural immune defences by preventing the bone marrow from producing enough healthy white blood cells.

Surgery This can make you more likely to get an infection because it makes a break in the skin or mucous membranes, which are part of the body's natural defences. The likelihood of getting an infection is increased if an operation involves removal of the spleen. The spleen is an important part of the immune system, and so removing it will mean that the person has a permanently reduced immunity and may need to take antibiotics to protect themselves from infection.

Radiotherapy This often has a mild temporary effect on the immune system but this is unlikely to cause any problem, except for people who have had radiotherapy to their whole body (total body irradiation). During total body irradiation, all the bone marrow in the body receives a dose of radiation that temporarily lowers the production of white blood cells, so the person will be at risk of infection for a while.

Chemotherapy This can often have a major effect on the immune system and may reduce the body's defences against infection for some months, both during and after treatment. This is because chemotherapy reduces the production of white blood cells by the bone marrow. People having chemotherapy are particularly at risk of picking up infections between 7–14 days after the chemotherapy, when the level of white blood cells will be at its lowest (this time is known as the nadir). This time can vary slightly depending upon the chemotherapy drug, or combination of drugs, used.

Infections can usually be effectively treated with antibiotics. If an infection is not treated quickly it can be much more difficult to get under control. Therefore, it is very important to contact your doctor or the hospital straight away if:

• your temperature goes above 38ºC (100.5ºF), or
• you suddenly feel unwell (even with a normal temperature).

These are signs of a possible infection and you may need to have antibiotic treatment, either as tablets or by drip (intravenous injection).

When your immunity is reduced for any reason, it is advisable to avoid other people who have sore throats, colds, flu, diarrhoea and vomiting, or other kinds of infection, such as chickenpox. If you do come into contact with anyone who has an obvious infection, it is best to ask your hospital doctor or specialist nurse for advice as soon as possible, as you may need to have medicines to prevent you from getting the infection.

It is important to go outside to get some exercise and fresh air during or after cancer treatment, but it is best to avoid crowds where possible. This includes avoiding using public transport, particularly during the rush hour, and crowded shopping centres, where you may be mingling with people who have an infection that is not obvious.

It is best to avoid going swimming or using a public jacuzzi when your immunity is reduced, due to the risk of picking up an infection from the water or in the changing room. Again, avoid crowds when doing other sports or social activities.

If you have pets or work with animals you will need to be extra careful if your immunity is reduced. It is usually safe to pet or stroke animals as long as you wash your hands thoroughly afterwards. It is best to avoid handling any animal waste, such as litter trays or manure, as this can increase your chances of getting an infection.

While you have reduced immunity you should be careful to avoid places where a fungus called aspergillus is likely to be. This can grow in dead leaves, grain stores, compost piles or other decaying vegetation. Brick, mortar and cement dust may also contain this fungus.

If you usually have a flu jab to help you avoid getting flu, it is quite safe to have the injection if your immunity is reduced. The flu jab is an inactivated vaccine, which means that it cannot harm you, but depending on the type of cancer and treatment you have had, the vaccine may not give you quite as much protection against flu as in previous years. Generally, people with cancer are recommended to have the vaccine at least two weeks before starting treatment or between their chemotherapy cycles, and then yearly.

If you are planning a holiday abroad, check with your GP first as some vaccines (known as live attenuated vaccines) should be avoided. These include measles, mumps, rubella and MMR, oral poliomyelitis liquid, oral typhoid, BCG and yellow fever.

If you have a weakened level of immunity, your family and friends should also avoid having the oral typhoid vaccination.

Some vaccines, such as poliomyelitis, can be given in an inactivated form.

One of the most effective ways of avoiding infection is to maintain a high standard of personal hygiene. It is important to remember always to wash your hands when you have been to the toilet and before you are about to prepare or eat food.

It is also a good idea to take a daily shower or bath, if possible. However, it is not advisable to share towels or flannels with other family members, due to the possible risk of cross-infection.

Some people receiving cancer treatment have central lines. These are long, hollow tubes made of silicone rubber. They are also called tunnelled central venous catheters. A central line is inserted (tunnelled) under the skin of your chest into a vein. The tip of the tube sits in a large vein just above your heart. Central lines are used to give medicines intravenously and can also be used to take blood samples.

A PICC is a long, thin, flexible tube that is inserted into one of the large veins of the arm near the bend of your elbow. It is then pushed into the vein until the tip sits in a large vein just above your heart.

A central line or PICC line can stay in place for many months. If you have a central line or a PICC line, it is necessary to protect it from bacteria and possible damage. Your hospital nurse or district nurse can give you advice about how to keep it clean. Often, a transparent dressing is used that can be changed weekly and will not be affected by a shower or bath.

When your immunity is low, your mouth is another place in which you can develop an infection. You will need to take extra care to keep your mouth clean. Use a soft toothbrush that is not too abrasive, as a hard brush might cause the gums to bleed, which can increase the risk of infection.

Your doctor may prescribe antiseptic mouthwashes to be taken after meals and at night. Sometimes they may also prescribe antifungal mouthwashes or lozenges. If they are used regularly they can help to prevent infection from developing.

Drinking plenty of fluids can help to prevent infection. Fluids help to keep your mouth moist and healthy, and will also flush out your kidneys and bladder – which prevents the build-up of debris in which bacteria can grow. It is thought that drinks such as cranberry juice may also help to reduce the risk of developing urine infections.

For a variety of reasons, people often find it difficult to eat and drink when they have cancer. It may be due to the cancer itself or the side effects of treatment. For example, you may feel sick (nauseous), or have taste changes that affect your appetite. It is important to try to eat a healthy balanced diet, however, as this will help to maintain your immune system.

Some foods, especially shellfish, poultry and eggs, can have harmful bacteria in them. These bacteria are usually killed by heat or made less harmful by cold. It is advisable to ensure that all food is stored at the correct temperature and cooked thoroughly. It is also a good idea not to reheat food that has cooled, as this may allow bacteria to regrow.

You may be recommended to follow a 'clean' diet. This means avoiding salads that could be dirty and avoiding foods that could contain harmful bacteria. These include:

• raw or lightly cooked eggs
• shellfish
• liver pâté
• soft cheeses
• takeaway food.

Advice on following a 'clean' diet will vary, depending on the type of cancer you have and the treatment you are receiving. For example, the guidelines might be very strict if you have leukaemia and are having high doses of chemotherapy or have had a bone marrow transplant, so it is best to check your diet with the hospital staff who are caring for you.

Your food needs to be carefully prepared, so that infection cannot pass from one food to another. All food should be used within its 'use by' date and care should be taken to keep raw and cooked foods apart. It is also important to keep clean foods away from potentially dirty foods, such as those mentioned above.

Try to eat as varied a diet as possible, especially the recommended five helpings of fruit and vegetables every day. These contain essential vitamins and minerals, which should help to keep you healthy. Peel fruit and vegetables before use and wash them thoroughly. You may find it best to eat fruits that are easy to peel, such as bananas and oranges. You could also crush them, to drink as fresh fruit juice.

This section has been compiled using information from a number of reliable sources, including:

• Oxford Textbook of Oncology (2nd edition). Souhami et al. Oxford University Press, 2002.
• Cancer and Its Management (5th edition). Souhami and Tobias. Oxford Blackwell Scientific Publications, 2005.
• Arrowood and Hayney in The Annals of Pharmacotherapy (36), pp1216–29, 2002.

For further references, please see the general bibliography.