Varicella, also known as chicken pox, is a highly contagious febrile rash illness caused by primary infection with varicella-zoster virus (VZV).  It is a reportable disease in Illinois.

Please see the CDPH Varicella Job Aid for Providers for important information about varicella, including information on testing and specimen requirements.

For more information about collecting specimens click here.

Case Classifications:
  • Confirmed Case: An acute illness with maculo-papulovesicular rash and epidemiologic link to another confirmed case or laboratory confirmation. Unvaccinated person with 200-400 lesions. 
  • Probable Case: An acute illness with maculo-papulovesicular rash and lack of epidemiologic link to another confirmed or probable case or lack of laboratory confirmation. 
  • Breakthrough Case: Vaccinated cases that are milder, less contagious, have lower fever and fewer lesions (<50). Lesions are often maculopapular instead of vesicular. Atypical appearance often leads to misdiagnosis. Consider laboratory confirmation given atypical appearance.

Role Of CDPH

What Is the Role of the Chicago Department of Public Health?


Provide education and technical assistance to providers


Conduct  public health investigation on all positive cases by confirming patient diagnosis; ensure appropriate medical follow-up; locate persons who may have been exposed; and provide education on post-exposure prophylaxis.


Implement control measures for outbreaks


Provide training, education and access to the Illinois National Disease Surveillance System


Ensure provider reporting is completed on all chicken pox cases

Varicella Resources

Clinical Features

Confirmed/Probable Cause

Probable Case

  • Rash generally appears first on the head and is most concentrated on the trunk.
  • Those who have not been vaccinated with the varicella vaccine will have a generalized rash that is pruritic and progresses rapidly from macules to papules to vesicular lesions before crusting.
  • Lesions are usually 1 to 4mm in diameter.
  • Healthy children will usually have 200 to 500 lesions in 2 to 4 successive crops.

Breakthrough Case

Breakthrough varicella is defined as a case of varicella due to infection with wild-type VZV occurring more than 42 days after varicella vaccination.


Probable Case

  • Less than 50 Lesions
  • Lesions are commonly papules that do not progress to vesicles
  • Shorter in duration with a lower incidence of fever

Herpes Zoster Virus (Shingles):

Characterized by vesicular lesions in one dermatome. Many labs automatically report + VZV PCRs to the health department. Talk to your lab about filtering out shingles results so they are not reported to CDPH.

Herpes Zoster Virus (Shingles)

Shingles is not a reportable disease

Varicella Reporting

To report suspect  Cases, use the Online Case Reporting Form


OR contact the CDPH Disease Reporting Hotline at 312-743-9000 

*After hours, weekends, and holidays, call 311 and ask for the communicable disease physician on-call (or 312-744-5000 if outside the City of Chicago). 

Schools:  Please click here for reporting and management information.

Suspect Cases should be reported within 24 hours.  

Do not wait for laboratory confirmation.
To Report Cases:Online Case Report Form (preferred)

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Varicella Contacts

Suspect Cases should be reported within 24 hours.

Do not wait for laboratory confirmation.

To Report Cases: Online Case Report Form (preferred)

For Clinical Questions or to Report by Phone: