Chickenpox : Causes, incidence, and risk factors

Chickenpox is a viral infection in which a person develops extremely itchy blisters all over the body. It used to be one of the classic childhood diseases. However, it has become much less common since the introduction of the chickenpox vaccine.

Causes, incidence, and risk factors

Chickenpox is caused by the varicella-zoster virus, a member of the herpesvirus family. The same virus also causes herpes zoster (shingles) in adults.

Chickenpox can be spread very easily to others. You may get chickenpox from touching the fluids from a chickenpox blister, or if someone with the disease coughs or sneezes near you. Even those with mild illness may be contagious.

A person with chickenpox become contagious 1 to 2 days before their blisters appear. They remain contagious until all the blisters have crusted over.

Most cases of chickenpox occur in children younger than 10. The disease is usually mild, although serious complications sometimes occur. Adults and older children usually get sicker than younger children.

Children whose mothers have had chickenpox or have received the chickenpox vaccine are not very likely to catch it before they are 1 year old. If they do catch chickenpox, they often have mild cases. This is because antibodies from their mothers' blood help protect them. Children under 1 year old whose mothers have not had chickenpox or the vaccine can get severe chickenpox.

Severe chickenpox symptoms are more common in children whose immune system does not work well because of an illness or medicines such as chemotherapy and steroids.

Symptoms

Most children with chickenpox have the following symptoms before the rash appears:

• Fever
• Headache
• Stomach ache

The chickenpox rash occurs about 10 to 21 days after coming into contact with someone who had the disease. The average child develops 250 to 500 small, itchy, fluid-filled blisters over red spots on the skin.

• The blisters are usually first seen on the face, middle of the body, or scalp
• After a day or two, the blisters become cloudy and then scab. Meanwhile, new blisters form in groups. They often appear in the mouth, in the vagina, and on the eyelids.
• Children with skin problems such as eczema may get thousands of blisters.

Most pox will not leave scars unless they become infected with bacteria from scratching.

Some children who have had the vaccine will still develop a mild case of chickenpox. They usually recover much more quickly and have only a few pox (less than 30). These cases are often harder to diagnose. However, these children can still spread chieckenpox to others.

Signs and tests

Your health care provider can usually diagnose chicken pox by looking at the rash and asking questions about the person's medical history. Small blisters on the scalp usually confirms the diagnosis.

Laboratory tests can help confirm the diagnosis, if needed.

Treatment

Treatment involves keeping the person as comfortable as possible. Here are things to try:

• Avoid scratching or rubbing the itchy areas. Keep fingernails short to avoid damaging the skin from scratching.
• Wear cool, light, loose bedclothes. Avoid wearing rough clothing, particularly wool, over an itchy area.
• Take lukewarm baths using little soap and rinse thoroughly. Try a skin-soothing oatmeal or cornstarch bath.
• Apply a soothing moisturizer after bathing to soften and cool the skin.
• Avoid prolonged exposure to excessive heat and humidity.
• Try over-the-counter oral antihistamines such as diphenhydramine (Benadryl), but be aware of possible side effects such as drowsiness.
• Try over-the-counter hydrocortisone cream on itchy areas.

Medications that fight the chickenpox virus are available but not given to everyone. To work well, the medicine usually must be started within the first 24 hours of the rash.

• Antiviral medication is not usually prescribe to otherwise healthy children who do not have severe symptoms. Adults and teens, who are at risk for more severe symptoms, may benefit from antiviral medication if it is given early.
• Antiviral medication may be very important in those who have skin conditions (such as eczema or recent sunburn), lung conditions (such as asthma), or who have recently taken steroids.
• Some doctors also give antiviral medicines to people in the same household who also develop chickenpox, because they will usually develop more severe symptoms.

DO NOT GIVE ASPIRIN OR IBUPROFEN to someone who may have chickenpox. Use of aspirin has been associated with a serious condition called Reyes syndrome. Ibuprofen has been associated with more severe secondary infections. Acetaminophen (Tylenol) may be used.

A child with chickenpox should not return to school or play with other children until all chickenpox sores have crusted over or dried out. Adults should follow this same rule when considering when to return to work or be around others.

Expectations (prognosis)

Usually, a person recovers without complications.

Once you have had chickenpox, the virus usually remains dormant or asleep in your body for your lifetime. About 1 in 10 adults will have shingles when the virus re-emerges during a period of stress.

Complications

Rarely, serious bacteria infections such as encephalitis have occured. Other complications may include:

• Reye's syndrome
• Myocarditis
• Pneumonia
• Transient arthritis

Cerebellar ataxia may appear during the recovery phase or later. This involves a very unsteady walk.

Women who get chickenpox during pregnancy can pass the infection to the developing baby. Newborns are at risk for severe infection.

Calling your health care provider

Call your health care provider if you think that your child has chickenpox or if your child is over 12 months of age and has not been vaccinated against chickenpox.

Prevention

Because chickenpox is airborne and very contagious before the rash even appears, it is difficult to avoid.

A vaccine to prevent chickenpox is part of a child's routine immunization schedule. For information, see: Chickenpox vaccine

The vaccine usually prevents the chickenpox disease completely or makes the illness very mild.

Talk to your doctor if you think your child might be at high risk for complications and might have been exposed. Immediate preventive measures may be important. Giving the vaccine early after exposure may still reduce the severity of the disease.

References

1. Myers MG, Seward JF, LaRussa PS. Varicella-zoster virus. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 250.
2. American Academy of Pediatrics Committee on Infectious Diseases. Recommended immunization schedules for children and adolescents--United States, 2008. Pediatrics. 2008;121:219-220. [PubMed: 18166576]
3. This article uses information by permission from Alan Greene, M.D., © Greene Ink, Inc.