Varicella and Zoster, 2011

Unusual case incidence, individual critical cases, and deaths due to varicella and zoster are reportable. The reporting rules allow for the use of a sentinel school surveillance system to monitor varicella and zoster incidence until the system no longer provides adequate data for epidemiological purposes, at which time case-based surveillance will be implemented. This summary represents the sixth full year of surveillance.

Six cases of critical illness, but no deaths, due to varicella were reported. All 6 were hospitalized for 4 to 8 days. Complications included meningitis and bacterial super-infection. Two cases had an underlying medical condition and recent history of treatment with immunosuppressive drugs. Both were children with juvenile rheumatoid arthritis and bo th were being treated with methotrexate. 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 adults, 2 were not vaccinated due to parental refusal, and 1 was a very recent immigrant to the United States. Vaccination history for the other case, age 20, was unknown.

An outbreak of varicella in a school 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 contagious. During the 2011- 2012 school year, we received reports of outbreaks from eight schools in eight counties involving 69 students and no staff. By comparison, we received reports of outbreaks from five schools in five counties involving 31 students and no staff during the 2010-2011 school year. The number of cases per outbreak ranged from 5 to 15 (median, 8.5) during the 2011-2012 school year compared with 5 to 11 (median, 5) during the 2010-2011 school year.

Surveillance data also include individual cases from sentinel schools throughout Minnesota; these data are used to extrapolate to the statewide burden of sporadic disease. Eighty schools were selected and participated throughout the 2011-2012 school year. A case of varicella is defined as an illness with acute onset of diffuse (generalized) maculopapulovesicular rash without other apparent cause; however, sentinel sites have been requested to also report possible breakthrough infection that may present atypically. During the 2011-2012 school year, 35 cases were reported from 19 schools. None of the schools reported a cluster of cases that met the outbreak definition. Based on these data, an estimated 632 sporadic cases of varicella would have been expected to occur during a school year among the 898,717 total school-aged children representing 0.07% of this population, for an incidence rate of 70.5 per 100,000 population. Most cases occurred among elementary school students, with an estimated incidence rate of 130.2 per 100,000 (536 of 411,536).

Case-based reporting of varicella in all child care settings was initiated in February 2010. In 2011, we received reports of 56 cases from 40 facilities. Fifty-four (96%) were <6 years of age. By comparison, 111 cases were reported from February to December 2010.

All suspected or confirmed cases of zoster with disseminated disease or complications other than post-herpetic neuralgia, irrespective of age, are reportable. During 2011, 50 cases were reported; 44 were hospitalized. Twenty-four cases were 60 years of age and 9 were <30 years of age. Twentythree (46%) had underlying conditions or were being treated with immunosuppressive drugs. Fifteen cases had disseminated disease, 14 had meningitis, 9 had encephalitis or meningoencephalitis, 7 had bacterial super-infection, and 7 had severe ocular involvement. Two cases with encephalitis subsequently died.

We currently conduct zoster surveillance in all schools. During the 2011- 2012 school year, 62 cases were reported from schools in 27 counties, representing 0.01% of the total school population of 898,717 for an incidence rate of 6.2 per 100,000 population. Ages ranged from 6 to 18 years. As compared to varicella, which is often diagnosed by school heath personnel and parents, most (91%) of the 58 zoster cases for whom an interview could be obtained were provider-diagnosed. All cases of zoster in individuals <18 years of age are reportable. Additional cases in children <18 years old were reported by child care sites (4 cases) and by providers (44 cases). In addition, death certificate data were reviewed to identify zoster-related deaths in 2011. Three deaths were identified; all were >60 years of age.

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 3-6 and grades 10-12 during the 2012-2013 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 need 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.

• For up to date information see>> Varicella (Chickenpox)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2011