Childhood Diseases

Updated 27 March 2018

Diagnosing chicken pox

It is easy to identify the rash of blisters of chicken pox, so laboratory test are not necessary.


Worldwide, chicken pox is one of the most common childhood infectious diseases. In countries with moderate climates like South Africa, most cases occur before the age of 10 years. 

The epidemiology is, however, less well understood in tropical areas, where a relatively large proportion of adults are seronegative, according to the World Health Organization (WHO).

People who are seronegative show no significant level of antibodies in their blood that indicates previous exposure to the chicken pox virus (varicella virus or VZV).

In Africa, risk factors for VZV include the rapidly increasing elderly population and a high HIV prevalence. Note that chicken pox is a vaccine-preventable infection, but that routine vaccination isn’t currently available in the South African public sector. Vaccination is readily available in the private sector.

How is chicken pox diagnosed?

Chicken pox is usually an easily recognisable disease because of the distinctive rash of blisters. For this reason, laboratory tests usually aren’t necessary.

If there’s doubt, a virology laboratory can do rapid tests on fluid obtained from a vesicle with a tiny needle and syringe, or on cellular material obtained by swabbing the raw base of a vesicle.

In situations of exposure to chicken pox, the knowledge that a person has definitely had chicken pox before is useful when deciding what measures, if any, need to be taken. Often this information isn’t known or is incorrect, such as when adults try to recall whether they had chicken pox as a child.

In circumstances where an at-risk person has been exposed to chicken pox, a blood test can be done to show whether they have antibodies to the varicella-zoster virus.

The presence of antibodies means that they had chicken pox in the past and that they’re therefore wholly or partially protected (as with immune-compromised people).

Reviewed by paediatrician Prof Eugene Weinberg. MBChB; FCP (SA); PAED (SA). March 2018.