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http://www.reutershealth.com/archive/2002/06/06/eline/links/20020606elin007.html

Chickenpox strikes twice more often than thought

Last Updated: 2002-06-06 12:05:17 -0400 (Reuters Health)

By Alison McCook

NEW YORK (Reuters Health) - A new study has found that quite a few people with chickenpox say they've already had a bout of the spot-causing ailment, suggesting that such repeat infection may be more common than previously thought.

Typically, one infection is thought to confer a lifelong immunity to future chickenpox infections.

Investigators led by Susan Hall of the University of North Carolina at Chapel Hill, report that 13% of cases of chickenpox reported in 1999 from one US region occurred in people who believed they had already had chickenpox. Interestingly enough, almost half of those suspected of double infections said that other members of their families had also had chickenpox twice.

The doctors who diagnosed either the first or second infections may have mistaken another similar condition for chickenpox, "or, maybe, a small proportion of people can, in fact, have a second infection," study author Dr. Jane Seward of the US Centers for Disease Control and Prevention told Reuters Health.

The investigators determined the rate of reported second infections from an examination of all reported cases of chickenpox in a region of Los Angeles county, from 1995 to 1999. In 1995, 4.5% said they'd already had chickenpox once while that number was 13% in 1999.

It has long been believed that a single infection with chickenpox leaves the body immune to subsequent bouts of the disease. So how could some people develop chickenpox twice? The answer, Seward said, may lie in the first infection's inability to completely immunize a person against the disease.

Chickenpox is caused by the varicella virus, a member of the herpes family that behaves somewhat differently from other viruses, Seward explained. For instance, a person can develop chickenpox at a young age, but may later, as an adult, acquire shingles--a painful outbreak of blisters on the body trunk, which is caused by a reactivation of varicella in the body.

"It may be that some people just don't develop a high enough antibody response to be protective," Seward said. "That dogma (that one case of chickenpox leaves a person immune for life) may not be absolute dogma," she added.

However, in an interview with Reuters Health, Seward and a co-author on the study, Dr. Aisha O. Jumaan of the Los Angeles County Department of Health Services, said that many of these double cases may stem from infections with a different virus that resembles chickenpox.

"They look like chickenpox, they act like chickenpox...but some other diseases can mimic chickenpox," Seward noted.

Indeed, in the study, published in the June 6th issue of the journal Pediatrics, the authors presented two cases in which the patients truly appeared to have developed chickenpox twice during their childhood. Both illnesses in the two patients produced crusted lesions as in chickenpox, and both could be tied to direct exposure to other infected people.

However, the researchers emphasized that even though the symptoms appeared to be chickenpox, the cases would need to be definitively diagnosed in a laboratory to be confirmed as chickenpox. Therefore, the two children, despite appearances, may only have developed the disease once.

Those with double infections tended to develop the disease for the first time at a relatively young age, and the condition took on a relatively mild form, the report indicates.

Seward and Jumaan recommend that doctors carefully document any doubts they have about a child's diagnosis, and perhaps vaccinate any children who may have been mistakenly diagnosed in the past.

Since the chickenpox vaccine was introduced in the US in 1995, the number of cases of this common childhood ailment has dropped dramatically.

SOURCE: Pediatrics 2002;109:1068-1073.

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