School, child care and camp exclusion policies for chickenpox: A rational approach
Posted: Aug 16 2018
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Natalie A. Bridger; Canadian Paediatric Society, Infectious Diseases and Immunization Committee
Paediatr Child Health 2018, 23(6):420–423.
Widespread varicella vaccination in Canada since 2007 has changed the epidemiology of chickenpox, with a significant decline in varicella-related hospitalizations. However, there will always be a varicella-susceptible population because of immune-compromising treatments or conditions and/or parental vaccine refusal. This document updates and replaces a 1999 statement by the Canadian Paediatric Society. The CPS position on school and child care exclusion policies has not changed since the original statement, but because there have been two published reports of varicella outbreaks associated with summer camp attendance since 1999, this revision provides additional recommendations to mitigate risk for varicella transmission at summer camps.
Keywords: Chickenpox; Child care; Exclusion; IMPACT; Summer camp; Vaccine; Varicella
Since publication of the Canadian Paediatric Society position statement on this topic in 1999 , varicella (chickenpox) vaccine has become a publicly funded routine childhood vaccine and the epidemiology of chickenpox in Canada has shifted. While chickenpox is no longer a common childhood illness, immunocompromised children remain at risk for severe or complicated varicella-related disease . Moreover, underlying conditions or medical treatments leading to immune compromise sometimes preclude receiving the varicella vaccine. Summer camps for children with specific chronic health conditions exist in Canada. While such camps provide invaluable experiences for such children, potential also exists for varicella transmission.
This statement updates the original CPS document to reflect the changing epidemiology of varicella-related disease in Canada and provides recommendations for summer camp exclusion policies.
Many local school and child care policies still require children with chickenpox to stay home until their rash has crusted over or cleared. Since 1994, however, the CPS has only recommended exclusion when children are so ill as to require more care than can be provided by school or child care personnel . They also recommended that children with mild illness be permitted to return to child care or school as soon as they feel well enough to participate normally in all activities, regardless of their state of rash.
By contrast, the American Academy of Pediatrics (AAP) recommends that “children with uncomplicated varicella may return when the rash has crusted or, in immunized people without crusts, until no new lesions appear within a 24-hour period” .
Because of policy differences between Canada and the USA, some practitioners and public health officials are reluctant to shift toward more relaxed exclusion criteria, even for children who feel well. Excluding an otherwise well, active child with mild illness from child care or school until all their lesions have crusted can be costly to parents, who may need to miss work or pay for alternative care.
Humans are the only known reservoir for the varicella-zoster virus (VZV), which causes chickenpox. This once-common childhood infection remains quite contagious in any communal setting. A 1950 report  established that in one school-based outbreak, 61 of 67 susceptible children in kindergarten through the fourth grade contracted chickenpox. The incubation period for chickenpox is usually 14 to 16 days but can be as short as 10 days or as long as 21 days after contact .
Epidemiology reports indicate that chickenpox may be acquired from contact with a case 24 to 48 hours before the development of the rash . Hospital outbreaks of chickenpox have occurred when the only possible route of transmission was airborne, suggesting that VZV can be contracted by inhalation. The virus then replicates in the nasopharynx or upper respiratory tract . VZV can be isolated from vesicular fluid obtained within the first 3 days of rash onset. Also, although viral cultures of nasopharyngeal secretions usually test negative, application of the more sensitive polymerase chain reaction (PCR) method can readily detect VZV DNA in these secretions on the day before rash onset, with the highest quantity of VZV DNA becoming detectable on day one of rash onset . These data, along with yields from outbreak investigations of children with chickenpox and herpes zoster, support the hypothesis that the virus is transmitted from both the respiratory tract and in aerosolized virus from skin lesions . Studies also suggest a direct and strong correlation between higher viremia and more severe clinical disease (i.e., higher, more prolonged fever and more vesicles) . This relationship suggests that excluding children who are too ill to participate fully in routine activities would also effectively exclude those with the highest viremia, who may be more infectious.
Therefore, both epidemiology and PCR virology data indicate that excluding children from school or child care after the chickenpox rash has developed and been diagnosed is too late to prevent VZV exposure of fellow classmates. There are no data to show that an exclusion policy that starts when chickenpox is diagnosed slows down the spread of chickenpox in school or child care settings. One study from 1991 evaluated the effectiveness of a 7-day-from-rash-onset exclusion policy in two Ohio schools . Transmission was highest in the prodrome period (i.e., the day before onset of the rash). No transmissions were documented after the index children returned to school, even though 15 returned < 5 days after onset of rash.
HOW HAS THE VARICELLA VACCINE CHANGED EPIDEMIOLOGY IN CANADA?
In 1999, the National Advisory Committee on Immunization (NACI) recommended universal varicella vaccination at 12 to 18 months of age. By 2007, each province and territory had introduced universal one-dose varicella vaccine programs .
In 2010, NACI updated their recommendations to include a second childhood dose of varicella vaccine to address the issues of primary vaccine failure and waning immunity. Most provinces and territories have since adopted this recommendation.
Because varicella is under-reported in Canada, it is difficult to estimate the current incidence of disease. In the prevaccine era, the annual incidence of chickenpox was approximately 350,000 cases, with between 1,500 and 2,000 hospitalized cases. Fifty per cent of children had had chickenpox by age 5 and 90% by age 12 . Since the introduction of universal one-dose varicella vaccine, the Immunization Monitoring Program ACTive (IMPACT) has reported a significant decline in varicella-related hospitalizations in every province and territory and in children of all ages . Reduced hospitalizations have also been observed in children younger than one year of age as well as in adults aged 20 to 39 and 40 to 59 (all three groups are outside the age groups for whom universal vaccine is recommended), which may indicate decreased VZV circulating in the community .
Breakthrough disease is usually defined by the onset of varicella-like illness occurring ≥42 days after immunization with varicella vaccine. Varicella-related illness can pose a diagnostic challenge because it often presents atypically (i.e., as a maculopapular eruption versus a classical vesicular rash) . With a one-dose varicella vaccine schedule, the estimated rate of breakthrough disease was 3.1% . A gradually increasing proportion of hospitalizations for breakthrough disease has been demonstrated in both Canada and the United States since the widespread use of one-dose varicella vaccine . This epidemiological development is not surprising given the overall reduction in hospitalizations for wild-type disease. Furthermore, one IMPACT study reported that 72% of hospitalized breakthrough varicella cases occurred in immune-compromised individuals . While persons with breakthrough disease can transmit VZV, there is some evidence to suggest that people who develop varicella postimmunization are less contagious than unvaccinated cases, particularly when they have fewer than 50 lesions .
While most Canadian epidemiology is derived from hospital data, the Centers for Disease Control and Prevention (CDC) in the USA conducted active surveillance in two regions from reporting sites that included hospitals and community settings (i.e., schools, child care centres, public health clinics, correctional facilities and homeless shelters) . Since the introduction of the two-dose varicella vaccine schedule in 2006, there has been a substantial decline in incidence, hospitalizations and outbreaks. It is worth noting, however, that the proportion of case patients aged 10 to 14 and 15 to 19 has increased. Also, the median age of vaccinated case patients has increased from 8 years (in 2006) to 9 years (in 2010) in one region and from 6 years (in 2006) to 7 years (in 2010) in the other. The median age of unvaccinated cases was higher in both regions. If a similar rise in age of infection is underway in Canada, this epidemiological shift could impact camp-going children and youth.
DOES VZV GO TO CAMP?
There are two published reports of varicella outbreaks at summer camps . The first occurred in Connecticut in 1997 at a camp for HIV-infected children. This was a 5-day camp with 110 campers aged 7 to 16 years. Before attending camp, forms were completed for all children and staff, indicating history of chickenpox or herpes zoster, as well as varicella immunization status. Children were excluded if they had been recently exposed to varicella. With this reporting process, 31 of the 110 campers and 4 of the 96 staff were deemed to be susceptible to varicella. Eleven of the 31 susceptible campers and 2 of the 4 susceptible staff developed varicella illness shortly after leaving camp. Two children were hospitalized, one of whom developed cellulitis. An outbreak investigation revealed that the most likely index case was a camper who had herpes-zoster infection during his stay but did not inform anyone of symptoms. The outbreak investigation also revealed that the information on varicella susceptibility and exposure provided to the camp was often incomplete.
The second outbreak occurred at a summer camp for children with chronic lung disease. The index patient was an 11-year-old boy with asthma, who developed classic chickenpox on the third day of camp. Camp staff were unaware that this child had been exposed to varicella 2 weeks before camp started. In this outbreak, 5 of 106 campers and 2 of 96 staff members developed chickenpox.
ARE EXCLUSION POLICIES FOR CHICKENPOX STILL RELEVANT?
Universal varicella vaccination has led to dramatically fewer hospitalized cases of varicella-related disease in Canada per year, which, though not an exact marker for circulating varicella in-community, certainly suggests that the burden of varicella-related disease has been reduced markedly across the country. And while breakthrough disease remains an issue, current evidence suggests both milder illness and decreased infectiousness in previously vaccinated individuals. Wider adoption of the two-dose vaccine schedule may help to reduce breakthrough disease. Ecological studies further suggest that ‘herd immunity’ may be enhanced by universal childhood vaccination, although accurate vaccine coverage rates would need to be known to ascertain this trend. However, despite the multiple beneficial effects of varicella vaccine, there continues to be a pool of varicella-susceptible children because of immune-compromising treatments or conditions and/or parental vaccine refusal. Also, as chickenpox becomes less common, a higher proportion of children are presenting with herpes-zoster infections, which is not prevented by herd immunity and has been linked to VZV transmission in schools and child cares settings . For these reasons, exclusion policies remain relevant.
The facts that chickenpox is no longer a common childhood illness and that clinical manifestations of the disease have become modified and attenuated in most immunized children, underscore the importance of educating the parents and caregivers of susceptible children about the signs, symptoms, transmission and incubation period of VZV.
Based on data presented in previous CPS statements and on current epidemiology, the Canadian Paediatric Society position on school and child care exclusion policies has not changed. The CPS recommends the following evidence-based polices for schools and child care settings:
- A child with mild illness should be allowed to return to school or child care as soon as she or he is well enough to participate normally in all activities, regardless of their state of rash.
- Parents, and particularly parents of immunosuppressed children, must be notified that chickenpox is in the classroom, and counselled regarding the VZV incubation period, as well as signs and symptoms.
- Parents of immunosuppressed children should be encouraged to seek medical advice to determine whether post-exposure prophylaxis is warranted.
For camp settings:
- All personnel and attendees should provide a complete history of varicella disease or immunization well before the camp start-dates.
- A list of potentially susceptible individuals should be developed and available to camp staff and administrators.
- Campers and staff who are susceptible to VZV should be offered immunization, provided there are no contraindications to vaccine use.
- Camps should review their varicella exclusion policies, taking the immune status of the camp clientele and the camp staff into consideration.
- When the camp includes persons with immunocompromising conditions, campers or staff with active VZV disease (varicella or zoster), or who have had an exposure to VZV in the past 21 days and are non-immune, should be excluded.
This position statement has been reviewed by the Community Paediatrics Committee of the Canadian Paediatric Society.
CANADIAN PAEDIATRIC SOCIETY INFECTIOUS DISEASES AND IMMUNIZATION COMMITTEE
Members: Michelle Barton-Forbes MD; Sean Bitnun MD; Natalie A. Bridger MD; Shalini Desai MD (past member); Michael Forrester MD (Resident member); Ruth Grimes MD (Board Representative); Nicole Le Saux MD (Chair); Timothy Mailman MD; Karina Top MD; Otto G. Vanderkooi MD
Liaisons: Upton D. Allen MBBS, Canadian Pediatric AIDS Research Group; Tobey Audcent MD, Committee to Advise on Tropical Medicine and Travel (CATMAT), Public Health Agency of Canada; Carrie Byington MD, Committee on Infectious Diseases, American Academy of Pediatrics; Fahamia Koudra MD, College of Family Physicians of Canada; Marc Lebel MD, IMPACT (Immunization Monitoring Program, ACTIVE); Jane McDonald MD, Association of Medical Microbiology and Infectious Disease Canada; Dorothy L. Moore MD, National Advisory Committee on Immunization (NACI); Howard Njoo MD, MHSc; Public Health Agency of Canada
Consultant: Noni E. MacDonald MD
Principal author: Natalie A. Bridger MD
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Disclaimer: The recommendations in this position statement do not indicate an exclusive course of treatment or procedure to be followed. Variations, taking into account individual circumstances, may be appropriate. Internet addresses are current at time of publication.