Risk Factors:

The varicella-zoster virus is responsible for both chickenpox and herpes zoster, but its method of infection is different in both diseases.

• Both the active varicella and zoster form of the virus can cause chickenpox.
• The shingles virus in its latent (inactive) form is never contagious.

Catching Chickenpox. Most people get chickenpox from exposure to other people with chickenpox. It is most often spread through sneezing, coughing, and breathing. It is so contagious that few nonimmunized people escape this common disease when they are exposed to someone else with the disease.

People can also catch chickenpox from direct exposure to a shingles rash if they have not been immunized by vaccination or a previous bout of chickenpox. In such cases, transmission happens during the active phase when blisters have erupted but not formed dry crusts. Herpes zoster spreads only from the rash. A person with shingles cannot transmit the virus by breathing or coughing.

Developing Shingles. Shingles itself can develop only from a reactivation of the varicella-zoster virus in a person who has previously had chickenpox. In other words, shingles itself is never transmitted from one person to another either in the air or through direct exposure to the blisters.

Risk Factors for Chickenpox (Varicella)

Between 75 - 90% of chickenpox cases occur in children under 10 years of age. Before the introduction of the vaccine, about 4 million cases of chickenpox were reported in the U.S. each year. Since a varicella vaccine became available in the U.S. in 1995, however, the incidence of disease and hospitalizations due to chickenpox has declined by nearly 90%.

The disease usually occurs in late winter and early spring months. It can also be transmitted from direct contact with the open sores. (Clothing, bedding, and other such objects do not usually spread the disease.)

A patient with chickenpox can transmit the disease from about 2 days before the appearance of the spots until the end of the blister stage. This period lasts about 5 - 7 days. Once dry scabs form, the disease is unlikely to spread.

Most schools allow children with chickenpox back 10 days after onset. Some require children to stay home until the skin has completely cleared, although this is not necessary to prevent transmission.

Risk Factors for Shingles (Herpes Zoster)

About 500,000 cases of shingles occur each year in the U.S. Anyone who has had chickenpox has risk for shingles later in life, which means that 90% of adults in the U.S. are at risk for shingles. Shingles occurs, however, in 10 - 20% of these adults over the course of their lives, so certain factors must exist to increase the risk for such outbreaks.

The Aging Process. The risk for herpes zoster increases as people age, and the overall number of cases will undoubtedly increase as the baby boomer generation gets older. One study estimated that a person who reaches age 85 has a 50% chance of having herpes zoster. The risk for postherpetic neuralgia (PHN) is also highest in older people with the infection and increases dramatically after age 50. PHN is persistent pain and is the most feared complication of shingles.

Immunosuppression. People whose immune systems are impaired from diseases such as AIDS or childhood cancer have a risk for herpes zoster that is much higher than those with healthy immune systems. Herpes zoster in people who are HIV-positive may be a sign of full-blown AIDS. Certain drugs used for HIV, called protease inhibitors, may also increase the risk for herpes zoster.

Cancer. Cancer places people at risk for herpes zoster. At highest risk are those with Hodgkin's disease (13 - 15% of these patients develop shingles). About 7 - 9% of patients with lymphomas, and 1 - 3% of patients with other cancers, have herpes zoster. Chemotherapy itself increases the risk for herpes zoster.

Immunosuppressant Drugs. Patients who take certain drugs that suppress the immune system are at risk for shingles (as well as other infections). They include:

• Azathioprine (Imuran)
• Chlorambucil (Leukeran)
• Cyclophosphamide (Cytoxan)
• Cyclosporine (Sandimmune, Neoral)
• Cladribine (Leustatin)
• Infliximab (Remicade)
• Adalimumab (Humira)

These drugs are used for patients who have undergone organ transplantation and are also used for severe autoimmune diseases caused by the inflammatory process. Such disorders include rheumatoid arthritis, systemic lupus erythematosus, diabetes, multiple sclerosis, Crohn's disease, and ulcerative colitis.

Risk Factors for Shingles in Children. Although most common in adults, shingles occasionally develops in children. Children with immune deficiencies are at highest risk. Children with no immune problems but who had chickenpox before they were 1 year old also have a higher risk for shingles.

Risk for Recurrence of Shingles. Shingles can recur, but the risk is low (1 - 5%). Evidence suggests that a first zoster episode boosts the immune system to ward off another attack.