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Chickenpox (Varicella)

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Reporting Obligations

Individuals who have or may have varicella shall be reported to the local Health Unit.

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Epidemiology

Aetiologic Agent

Varicella-zoster virus (VZV), the human (alpha) herpesvirus 3, is a member of the Herpesvirus group.

Clinical Presentation

VZV causes two separate diseases: varicella and herpes zoster (shingles). Varicella is the primary infection and is a reportable disease. Herpes zoster is the secondary infection caused by the reactivation of latent varicella infection and is not a reportable disease.

Varicella is an acute illness characterized by fever and generalized, pruritic, vesicular rash in varying, successive stages of development called “crops”. Lesions progress rapidly from maculopapular to vesicular rash, then crusts, resulting in granular scabs.

“Breakthrough varicella” can occur among vaccinated individuals characterized by mild, atypical and in apparent infections. Individuals are afebrile, have uncharacteristic few lesions with papules that do not progress to vesicles.

Fetal infection as a result of maternal varicella infection during the first and early second trimester of pregnancy will occasionally result in fetal death, congenital varicella syndrome (CVS) and other complications.

Modes of Transmission

Person to person by direct contact with Varicella zoster virus through droplet or airborne spread of vesicle fluid or secretions of the respiratory tract or indirectly by freshly contaminated fomites. Scabs are not infectious. Transmission to the fetus during pregnancy can also occur.

Incubation Period

10–21 days, commonly 14–16 days; may be shortened in the immunodeficient and prolonged as long as 28 days after passive immunization against varicella.

Period of Communicability

As long as five days but usually one to two days before onset of rash and until all lesions are crusted, usually about five days after the rash onset. Contagiousness may be prolonged in individuals with altered immunity.

Risk Factors/Susceptibility

Susceptibility is universal in persons not previously infected or vaccinated. Infection usually confers life long immunity. The virus remains latent in sensory ganglia and disease may recur years later as herpes zoster (shingles) in about 15% of adults and sometimes in children.

Diagnosis and Laboratory Testing

Laboratory confirmation of infection with clinically compatible signs and symptoms in the absence of recent immunization with varicella-containing vaccine. Caution must be taken when reviewing serological data without reference to the clinical evidence as the response to VZV reactivation (shingles) may be the same as to primary chickenpox. Optimal recovery of VZV is achieved if specimens (e.g., vesicle/lesion fluid or swab) are obtained 2–3 days after rash onset and from fresh vesicles.

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Treatment and Case Management

Cases of varicella that present with mild illness may be permitted to return to child care settings or school as soon as cases are well enough to participate in normal activities, regardless of the state of the rash. Exclusion of children from school or child care settings after the onset of the varicella rash is not expected to slow down the transmission. Parents and staff should be notified of varicella in a classroom, particularly those of immunocompromised children, in addition to pregnant staff.

Health care workers (HCWs) with acute varicella illness must be excluded from work until lesions are dried and crusted.

Treatment of cases where indicated is under the direction of the attending health care provider. Varicella infection in pregnancy requires prompt treatment initiated within 24–48 hours of rash onset to prevent maternal and fetal sequelae. Children in whom varicella disease occurred at <12 months of age should receive the routine two-dose varicella-containing vaccine schedule.

Contacts should be advised about signs and symptoms of VZV infection that can occur within 21 days after exposure and seek medical attention upon symptom onset. Univalent varicella vaccine should be administered to susceptible individuals within 3 days of exposure. Administration up to 5 days after exposure has been shown to be effective in preventing or reducing the severity of varicella.

Varicella zoster immune globulin (VarIg) should be considered for individuals at increased risk of severe varicella. Optimal benefit of VarIg is achieved if administered within 96 hours after first exposure, with protection lasting approximately three weeks. If VarIg is used between 96 hours to 10 days after exposure it may help to attenuate disease.

Pregnant contacts should be advised to consult with their physician promptly to confirm history of varicella vaccination or disease. If not confirmed, serologic testing should be performed. VarIg should be offered if serologic testing shows no immunity or cannot be obtained within 96 hours if there has been a significant exposure.

Patient Information

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Additional Resources

Ontario Hospital Association. “Varicella/Zoster (Chickenpox/Shingles) Surveillance Protocol for Ontario Hospitals.”

Heymann, D.L. Control of Communicable Disease Manual (19th Ed.). Washington, American Public Health Association, 2008.

Public Health Agency of Canada. “Canadian Immunization Guide, Varicella (Chicken Pox) Vaccine.”

Public Health Agency of Canada. “Canadian Immunization Guide, Herpes Zoster (Shingles) Vaccine.”

Ministry of Health and Long-Term Care. “Publicly Funded Immunization Schedule for Ontario”, December 2016.

References

Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2019.