Chickenpox

Chickenpox is an infection caused by the varicella-zoster virus. It is best known for its itchy rash of small fluid-filled blisters, which come in waves over several days and then dry into scabs.

Most cases are in children under fifteen, and in a healthy child the illness usually lasts about four to seven days. It is far more likely to be severe in newborn babies, teenagers, adults, pregnant women and anyone whose immune system is weak.

A fever, headache, tiredness and loss of appetite often come a day or two before the rash. The rash then passes through three stages, and because new spots keep appearing, all three stages are usually present at once:

• Small red or pink spots, which may show up anywhere, including the scalp, and inside the mouth and the genital area
• Blisters filled with fluid, which are very itchy and may burst
• Scabs, which may flake or leak a little before healing

The spots usually start on the chest, back and face and then spread. On darker skin the rash can be harder to see, so it helps to feel for the raised spots. It takes about a week for all of them to crust over.

See a doctor within a day or two if chickenpox appears in an adult or teenager, in pregnancy, or in someone with low immunity, if anyone in those groups has been near a person with chickenpox, if the fever carries on after the spots have scabbed, if spots become sore and weeping, or if the diagnosis is not clear.

The varicella-zoster virus spreads very easily. Most people who have never had chickenpox or the vaccine catch it after close contact with someone who has it.

It travels through the air from an infected person and through direct contact with the fluid in the blisters. A person is infectious from one or two days before the rash appears until every spot has scabbed over, usually about five days after the first spots. Chickenpox can also be caught from the blisters of someone with shingles. Symptoms begin ten to twenty-one days after contact.

• Never having had chickenpox or the chickenpox vaccine
• Close contact at home, school or nursery with someone who has it
• Being a newborn baby, particularly of a mother who has never had chickenpox
• Pregnancy
• Being a teenager or an adult, in whom the illness tends to be more severe
• A weakened immune system, from illness, cancer treatment, steroids or other medicines that lower immunity

The commonest problem is a bacterial infection of skin that has been scratched, which shows as redness, pain, swelling or yellow crusting around the spots. Dehydration is also common when the mouth is sore.

Less often, chickenpox affects the lungs or the brain, or causes problems in pregnancy for the mother or the baby. These serious problems are more likely in babies, teenagers, adults and people with a weakened immune system. Long after recovery the virus can wake up as shingles.

• The chickenpox vaccine, which prevents almost all severe illness; a doctor can advise on the course for a child or an adult
• Vaccination for people in close contact with those at risk, when a doctor advises it
• Staying away from school, nursery or work until every spot has scabbed over
• Keeping away from newborn babies, pregnant women and anyone with low immunity while infectious
• Seeing a doctor quickly after contact for anyone pregnant, newborn or with low immunity, because protective treatment may be given
• Covering coughs, washing hands and not sharing towels or bedding while the rash is present

Chickenpox is nearly always recognised by looking at the rash and asking about fever and contact with a case, so no test is usually needed. Telephone the clinic before going in, so that other patients are not exposed in the waiting room.

Tests are used when the diagnosis is uncertain, when the person has low immunity, or in pregnancy, where a blood test can show whether someone is already immune after contact with a case.

In a healthy child the illness passes on its own, and care is about comfort: plenty of fluids, paracetamol for fever and discomfort, loose cotton clothes, nails cut short, and socks or mittens at night for a small child who scratches in their sleep.

For the itch, a cool bath with the skin patted rather than rubbed dry, calamine lotion, a cooling gel or an oatmeal bath all help, and a doctor or pharmacist can suggest an antihistamine if the itching keeps a child awake. Aspirin must not be given to anyone under sixteen, because of the risk of a rare and serious condition called Reye syndrome, and ibuprofen is best avoided in chickenpox as it has been linked with serious skin infection.

Antiviral medicine is recommended for people more likely to become seriously ill, such as newborns, adults, pregnant women and those with low immunity, and it works best when started early. Anyone with signs of a skin infection, breathing trouble or dehydration needs to be seen, and some people need hospital care.