Varicella and Zoster, 2012

Since 2006, unusual case incidence, individual critical cases, and deaths due to varicella have been reportable. A sentinel school surveillance system was used to monitor varicella incidence. Because of the declining incidence of varicella disease, the sentinel system no longer provided adequate data for epidemiological purposes and was discontinued at the end of the 2011-2012 school year. Case based surveillance was implemented for all Minnesota schools beginning in September 2012 and for all other reporting entities beginning January 1, 2013. Case-based reporting of varicella in all childcare settings was initiated in February 2010. A case of varicella is defined as an illness with acute onset of diffuse (generalized) maculopapulovesicular rash without other apparent cause; however, reporting entities have been requested to also report possible breakthrough infection that may present atypically.

From case-based school surveillance for varicella conducted September 1 - December 31, 2012, we received 188 case reports from 117 schools in 35 counties. One hundred fifty-five were sporadic cases and 33 were outbreak associated cases. From case-based childcare surveillance conducted throughout 2012, we received reports of 65 cases from 47 facilities. Fifty were sporadic cases and 15 were outbreak-associated cases. Sixty-two (95%) of childcare cases were <6 years of age. By comparison, 56 cases were reported by childcare facilities in 2011. Varicella is often identified by childcare personnel or parents, as opposed to provider diagnosed.

An outbreak of varicella in a school or a childcare facility is defined as 5 or more cases within a 2-month period in persons <13 years of age, or 3 or more cases within a 2-month period in persons 13 years of age and older. An outbreak is considered over when no new cases occur within 2 months after the last case is no longer infectious. Two Minnesota schools reported outbreaks between September 1 - December 31, 2012. An outbreak in a school with grades pre-K to 12 included 30 students and one staff member. Prior to the outbreak, 8% of the students were unvaccinated for varicella and had no reported varicella disease history. Among students with no previous history of disease, the attack rate was 70% for unvaccinated students, 18% for students with 1 dose of varicella vaccine, and 2% for students with 2 doses of varicella vaccine. Of the 15 unvaccinated cases, 8 had moderate disease (250-499 lesions) or severe disease (>500 lesions). In contrast, of the 14 vaccinated cases, 13 had mild disease (<50 lesions), and 1 had moderate disease. In addition, three childcare facilities reported outbreaks in 2012. The source case for one of the outbreaks also attended pre-school at the school with the larger outbreak described above.

During 2012, 7 cases of critical illness due to varicella, but no deaths, were reported. All 7 were hospitalized for a range of 4 to 9 days. Complications included cerebellitis with ataxia, bacterial cellulitis, dehydration, anorexia, and myoclonus. One case had an underlying medical condition and recent history of treatment with immunosuppressive drugs. The other cases had no or unknown underlying conditions and were not known to be immunosuppressed. Five cases had not received varicella-containing vaccine; 2 were not vaccinated due to conscientiously held beliefs, 1 had a reported history of varicella disease, and 2 were adults. One of the adults, 93 years of age, had apparent recurrent varicella disease. Serologic testing performed at CDC detected high avidity for the virus, indicating past infection. One case had received 1 dose of vaccine prior to diagnosis of a condition requiring immunosuppressive therapy. Vaccination history for the remaining case, 22 years of age, was unknown.

Since 2006, the U.S. Advisory Committee on Immunization Practices has recommended 2 doses of varicella vaccine for children. The Minnesota school immunization law has required 2 doses of vaccine for students entering kindergarten and grade 7 since 2010. Students who will be in grades 4-6 and grades 11-12 during the 2013-2014 school year were beyond kindergarten or beyond grade 7 when the law was implemented and therefore were not included in the requirement. Children in these grades should be evaluated to determine whether they have had a second dose of varicella vaccine, particularly given the increased severity of varicella in older children and adults. Older adolescents and adults should also be evaluated for varicella immunity (history of varicella disease or 2 doses of varicella vaccine at least 4 weeks apart) and offered varicella vaccine if indicated, as varicella is more severe in adolescents and adults.

In the event of a school outbreak, children and staff who are susceptible to varicella because of incomplete vaccination or no history of disease are advised to be excluded from school from the 10th to 21st day after exposure.

All zoster cases in children <18 years of age are reportable. Cases may be reported by school health personnel, childcare facilities, or healthcare providers. During the spring and fall semesters of 2012, zoster cases in students were reported from 62 schools in 32 counties. Ages ranged from 3 to17 years (median, 13 years). Sixtyfour (94%) of the 68 zoster cases were provider-diagnosed. Additional cases in children <18 years old were reported during 2012 by childcare sites (4 cases) and by providers (39 cases). Overall, among the 90 cases for whom both varicella disease history and vaccination history were available, 49 (54%) had a history of disease but had not received vaccine, 28 (31%) had no history of disease but had received 1-2 doses of vaccine, and 13 (14%) had a history of disease and had received 1-2 doses of vaccine.

Zoster with dissemination or complications (other than post-herpetic neuralgia) in persons of any age is also reportable. During 2012, 41 zoster cases with dissemination or complications were reported; 33 were hospitalized. Twenty-four cases were 60 years of age or older; 12 were 30 to 59 years of age; and 5 were <30 years of age. Eighteen (4%) had underlying conditions or were being treated with immunosuppressive drugs. Seventeen cases had disseminated disease, 9 had meningitis, 8 had severe ocular involvement, 7 had encephalitis or meningoencephalitis, 3 had pneumonia, 2 had Ramsay-Hunt Syndrome, 2 had bacterial cellulitis, and 1 had Bell's palsy. One case with encephalitis subsequently died.

Zoster vaccine is licensed for adults 50 years of age and older, and is recommended for all adults 60 years of age and older regardless of whether they report a prior episode of herpes zoster.

Updated Thursday, 29-May-2014 13:24:33 CDT