Varicella and Zoster, 2013

Case-based surveillance for varicella was implemented January 1, 2013. Due to declining disease incidence in the post-vaccination era, the sentinel school program in place from 2006 through 2012 was no longer effective and was discontinued. During 2013, 478 cases (9 per 100,000 population) were reported. Two hundred seventy-four cases (57%) were reported from the metropolitan area. Cases ranged from 13 days to 63 years of age. Fifty-three (11%) cases were <1 year of age, 167 (35%) were 1-5 years of age, 167 (35%) were 6-12 years of age, 32 (7%) were 13-17 years of age, and 59 (12%) were >18 years of age.

Varicella cases continue to be associated with outbreaks, and in 2013, 72 cases (15%) were outbreak-associated. Six schools reported outbreaks in 2013. The largest outbreak occurred in a school with grades pre-K to 12 and included 22 students. Prior to the outbreak, 6.4% of the students in the school were unvaccinated for varicella and had no reported varicella disease history. Among students with no previous history of disease, the attack rate was 56% for unvaccinated students, 1% for students with 1 dose of varicella vaccine, and <1% for students with 2 doses of varicella vaccine. Of the 15 unvaccinated cases for which rash severity information was available, 2 were classified as mild (<50 lesions), 8 as moderate (50-249 lesions), 3 as moderately severe (250-499 lesions), and 2 as severe (>500 lesions). Both vaccinated cases had mild disease (<50 lesions).

Varicella tends to be more severe in individuals <1 year of age and in individuals >13 years of age. During 2013, 4 cases were hospitalized; no deaths were reported. Of the hospitalized cases, 1 was <1 year of age, 1 was 5 years of age, and 2 were >13 years of age with a total age range from 13 days to 51 years. One case was admitted for observation and 3 had complications including mild hepatitis, metabolic encephalitis, high fever, dehydration, and severe pain requiring management with morphine. Only 2 of the hospitalized cases had underlying conditions; 1 was immunosuppressed due to chemotherapy for cancer, and 1 had underlying medical conditions of pancreatitis and liver disease. None of the hospitalized cases had received varicella-containing vaccine: 1 was born outside of the United States, 1 was underage for the vaccine, and 2 were adults who were never offered the vaccine.

Varicella is often identified by parents/ guardians, as opposed to provider-diagnosed. Of the 457 cases for which an interview could be completed: 268 (59%) had visited a health care provider, 48 (10%) had consulted a provider by telephone, 8 (2%) had been identified by school health personnel, and for 133 (29%) no consult was obtained. Laboratory confirmation is recommended when the rash presents atypically. Testing is by PCR. Of the 424 cases for which test information was known, 82 (19%) had laboratory testing performed. Testing was more frequently performed in cases >18 years of age, of which 46 (85%) were tested.

Although vaccine coverage continues to increase, students who will be in grades 5-6 and grade 12 during the 2014-2015 school year may need a second dose of varicella vaccine. These students were beyond kindergarten and 7th grade at the time when the vaccine school requirement was implemented in 2010. 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. Since 2006, the U.S. Advisory Committee on Immunization Practices has recommended 2 doses of varicella vaccine for children. Older adolescents and adults should also be evaluated for immunity (history of varicella disease or 2 doses of vaccine at least 4 weeks apart) and offered vaccine if indicated.

All zoster cases in children <18 years of age are reportable. Cases may be reported by school health personnel, childcare facilities, or health care providers. During 2013, cases were reported from 69 schools in 32 counties. Ages ranged from 6 to17 years (median, 13 years). Sixty-two (89%) of 76 cases reported by schools were provider-diagnosed. Additional cases in children <18 years of age were reported during 2013 by childcare sites (5 cases) and by providers (26 cases). Overall, of 86 cases for whom both disease history and vaccination history were available, 44 (51%) had a history of disease but had not received vaccine, 14 (16%) had no history of disease but had received 1-2 doses of vaccine, 20 (23%) had a history of disease and had received 1-2 doses of vaccine, and 8 (9.3%) had no known history of disease or vaccination.

Zoster with dissemination or complications (other than post-herpetic neuralgia) in persons of any age is also reportable. During 2013, 55 zoster cases with dissemination or complications were reported; 50 were hospitalized. Thirty-two cases were 60 years of age or older, 16 were 30 to 59 years of age, and 7 were <30 years of age. Thirty (55%) had underlying conditions or were being treated with immunosuppressive drugs. Twenty-seven cases had disseminated disease, 13 had cellulitis or other bacterial superinfection,11 had meningitis, 8 had encephalitis or meningoencephalitis, 2 had pneumonia, and 1 had myelitis. One case with pneumonia and suspected bacterial superinfection and 1 case with meningoencephalitis subsequently died.

• For up to date information see>> Varicella (Chickenpox)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2013