Download Outbreak of Varicella in a School in Catania (Sicily)

Outbreak of Varicella in a School in Catania (Sicily)
Mario Cuccia (1)ᶠᵖ, Sebastiano Rinnone (1), Irene Maria C. Pulvirenti (2)
(1)ASP Catania Department of Prevention S. Gregorio di Catania Italy (2) University of Catania Department G. F.
Ingrassia Catania Italy
Introduction: Varicella is a highly contagious infectious disease, due to varicella-zoster virus which spreads
mainly via aerosolized droplet nuclei or direct contact with fluid from a varicella rash. The period of
communicability extends from 1 to 2 days before the onset of the rash through the first 5 to 6 days after
rash onset. The average length of incubation period is 14 to 16 days from exposure, with a range of 10 to
21 days. Varicella is commonly considered as a mild disease, but serious complications such as secondary
bacterial infections, pneumonia, encephalitis, cerebellar ataxia, transverse myelitis and rarely death can
occur among immunocompromised people, adults, and infants born to women infected during the firstsecond trimester of pregnancy or in the neonatal period. Varicella mainly affects children. In the United
States an attenuated single-antigen varicella vaccine was licensed in 1995, which resulted in a significant
decrease of the morbidity and mortality rates.
Since 2003, in Sicily (Italy), the varicella vaccine¹ has been offered to toddlers 12-15-month-old and
susceptible adolescents², from 2010 a second dose has been introduced at 5-6 years of age³. For
vaccination campaigns three vaccines have been used: the monovalents Varivax ® and Varilrix® and the
quadrivalent Priorix Tetra® for Measles, Mumps, Rubella and Varicella. In Sicily, the vaccination program
was taken up rapidly, with increasing coverage rates over time. A steady uptake of the program was
observed between 2003 and 2007, and the program’s target was achieved, with 87.5% coverage for the
birth cohort 2005⁴. In October 2011, in the province of Catania (1,087,000 inhabitants) the vaccination
coverage (VC) for the birth cohort 2008 was 83.13%, and for children born in 2009 it was 80.35%.
The reporting by pediatricians of 4 varicella cases in children attending the same primary school, gave us
an opportunity to identify an outbreak in this primary school in Catania. The outbreak occurred from
January to March 2011, the school was attended by 225 children distributed as follows: 3 kindergarten
classrooms (K) (age 3-5) and 5 primary classrooms (P) (age 6-10). The K classrooms and the P classrooms
are located on two different floors and they do not share any common space. The aim of this study, as
similar studies⁵, was to: 1) estimate the impact of varicella on a partially vaccinated population; 2) assess
the vaccine effectiveness in the field; and 3) evaluate indirect costs by school days missed.
Methods: An observational retrospective study was conducted by a questionnaire, administered by phone
to the parents of the 225 children to detect the following topics: number of cases and breakthrough
disease (cases occurring more than 42 days after vaccination), susceptibility status, vaccine type, doses and
coverage. Indirect costs were verified on school records, excluding holidays. The disease case definition is
based only on anamnesis and clinical signs.
Results: In figure 1 we show the susceptibility status and VC by classroom of the 225 children before the
outbreak by classroom: 147 vaccinated (129 one dose, 18 two doses); 32 unsusceptible (31 unvaccinated, 1
breakthrough disease after one dose), 47 susceptible. VC by section: 88.9% (K), 65% (P); VC by classroom:
K1 (82.7%); K2 (92.6%); K3 (92.3%); P1 (88.5%); P2 (72.2%); P3 (61.9%); P4 (63.1%); P5 (31.6%). The
distribution by vaccine type was: Varivax® (134), Varilrix® (5), and Priorix Tetra® (21). We registered 28 total
cases (Figure 2): 1 in K classrooms and 27 in P classrooms. All cases were among unvaccinated children
except 2 among single dose children vaccinated 7-8 years before. The two breakthrough disease cases had
a mild course, with less than 50 vesicles. No case required hospitalization. The index case was identified in a
nine-year-old boy attending the level 4 P classroom (Figure 3). The school days missed by the cases were
347 (average: 12.4/case). The attack rates estimated were: unvaccinated (K) 10.0%; vaccinated (K) 0;
unvaccinated (P) 67.5%; vaccinated (P) 2.9%.
Conclusions: 1) This study shows: a) the relevant vaccine effectiveness at least for a limited number of
years⁶; b) the significant indirect impact of the disease considering the school days missed; 2) considering
the different type of vaccine administered and the limited population, it was impossible to estimate the
vaccine efficacy. 3) The importance of monitoring cases of illnesses that are preventable by vaccination.
References:
1) M. Cuccia, S. Pollina Addario, A. Cernigliaro, V. Palmigiano. Ospedalizzazione per varicella in Sicilia
dopo l’introduzione della vaccinazione. http://www.epicentro.iss.it/ben/2009/marzo/1.asp
2) Regione Sicilia. Circolare regionale del 22 luglio 2002, n. 1087. Gazzetta Ufficiale Regione Siciliana,
16 agosto 2002.
3) Regione Sicilia. Decreto 13/7/2010; Nuovo calendario della Regione Sicilia. Gazzetta Ufficiale
Regione Siciliana, 6 agosto 2010.
4) G. Giammanco, S. Ciriminna, I. Barberi, L. Titone, M. Lo Giudice, LR Biasio. Universal varicella
vaccination in the Sicilian pediatric population: rapid uptake of the vaccination program and
morbidity trends over five years. Eurosurveillance 2009; 14(34).
5) Lai CC, Chen SC, Jiang DD. An Outbreak of Varicella among Schoolchildren in Taipei. BMC Public
Health. 2011 Apr 12;11(1):226.
6) K. Galil, E. Fair, N. Mountcastle, P. Britz, J. Seward. Younger Age at Vaccination May Increase Risk of
Varicella Vaccine Failure. J Infect Dis. 2002;186:102-5
Figure 1: Distribution of Varicella Susceptibility and
Vaccination Status by Classroom before the Outbreak
Figure 2: Distribution of Varicella Susceptibility and
Vaccination Status by Classroom after the Outbreak
Figure 3: Distribution of the Cases by Week and Classroom.