The present study evaluated the time trends in pediatric hospitalizations for varicella infection in a temperate region prior to the implementation of universal VZV immunization among infants and during which period climate changes were notable 
. The study also evaluated the association between the occurrence of hospitalized varicella cases and climatic variables during the aforementioned study period. The main study findings indicate that the occurrence of pediatric hospitalized varicella cases increased notably in the summer and decreased in the autumn seasons during the period 1982–2003. In particular, the most notable effects were observed in the September months of the period examined. The evidence provided supports that modifications in hospitalized varicella cases during the period 1982–2003 in the examined temperate Mediterranean region were associated with climatic factors. Specifically, the occurrence of hospitalized varicella cases was inversely associated with air temperature (p<0.001) and positively associated with wind speed (p
0.009). No statistically significant relationship was revealed between hospitalized varicella cases and relative humidity.
Changes in the epidemiology of varicella infection, particularly in tropical regions, have been attributed to demographic changes, including increased population density and urbanization 
. Seroprevalence rates of varicella infection have been observed to be higher among urban populations, regardless of the population"s age distribution 
. It has been proposed that in urban tropical regions an elevated population density may partially overcome the transmission-interrupting effect of a tropical climate 
. Specifically, urban settings may enable enhanced social interaction and population mobility, both within and between communities, and hence facilitate viral transmission 
. Such evidence is corroborated by findings in temperate countries indicating that children with enhanced social interaction, such as that incurred by their attendance in nurseries, are more likely to contract varicella infection 
. In the present reference population, a significant influx of immigrants was observed following the 1990′s. Immigrant children are more likely to be hospitalized for varicella complications 
. However, as compared to Greek children, immigrant children have lower day care attendance rates and consequently contract varicella at an older age 
. Since the mean age of hospitalized patients for varicella infection has not significantly changed during the study period 
, it is upheld that the aforementioned demographic changes did not markedly affect the epidemiological trends of hospitalizations for varicella infection in the population examined.
The study findings indicated that significant changes in the epidemiology of varicella infection have occurred during the seasons of summer and autumn. In particular, a diminishment in hospitalized varicella cases was observed during the September months. These findings corroborate with proposed hypotheses positing that changes in varicella infection rates in urban regions may be attributed to the combined effects of atmospheric air pollution and ultraviolet radiation 
The present study findings indicated that the modifications in the occurrence of hospitalized varicella cases in the evaluated temperate Mediterranean region were associated with climatic variables. In particular, the occurrence of hospitalized varicella cases was inversely associated with air temperature. Moreover, the frequency of hospitalized varicella cases was proximally associated with wind speed. Interestingly, although during the summer months of the period 1982–2003 an increase in mean air temperature was documented in the evaluated region, a concomitant increase in hospitalized varicella cases was also observed. However, the GLM analysis indicated that the potential effect of wind speed upon the occurrence of hospitalized varicella cases is substantially greater than that of mean air temperature. This is corroborated by the origin of the Greek term for “chickenpox” (“anemevlogia”) which is derived from the combination of the terms “anemos” (
wind) and “evlogia” (
small pox), indicating that the association between wind speed and varicella infection has been empirically suspected for several centuries. Therefore, it is upheld that the observed increase in hospitalized varicella cases in the summer months of the period 1982–2003 is more likely to be attributable to mean wind speed rather than mean air temperature.
Differential seroprevalence rates in varicella infection have been partly attributed to climatic factors, particularly in relation to temperature and humidity 
. Correlations between varicella incidence rates with both temperature and rainfall have been observed 
. In tropical regions, evidence supports that the mean of extreme minimum temperatures is most proximally associated with increases in VZV seroprevalence. Due to the heat sensitivity of VZV, the virus may be inactivated at higher temperatures 
. Hence, the viral transmission potential may be markedly reduced in countries with elevated mean temperatures and humidity 
. This has been primarily corroborated by the lower VZV seroprevalence rates observed in tropical regions 
Similarly, lower varicella seroprevalence rates in southern European countries have been attributed to the effects of the mild Mediterranean climate upon disease transmission potential 
. It has been suggested that both the high levels of humidity and diminishment in the seasonal variations in temperature, particularly in countries proximal to the equator, may be associated with a uniform distribution of varicella cases throughout the year 
. It is proposed that the observed epidemiological changes in the study region may be partly attributed to climatic changes which have resulted in the modifications of mean air temperature, relative humidity and, in particular, wind speed during the summer and autumn seasons 
. However, mounting evidence exists supporting that the risk of infection by airborne viruses via aerosol transmission may be equivalent to that of direct transmission 
, particularly in settings with low humidity 
. The study findings indicated that the peak incidence rate remained greatest during the spring season throughout the time period evaluated. This contrasts findings in tropical regions which indicate that the peak incidence of varicella infection occurs during the cooler months of the year 
. Thus, it may be inferred that although climatic changes in the study region have potentially influenced the seasonal distribution of varicella infection, the disease epidemiology still concurs with that of other temperate countries.
The strengths of present study include that it is the first of its kind to examine time trends in the epidemiology of pediatric hospitalized varicella cases over an extended time period in a temperate Mediterranean country. Data collected include more than four fifths of all patients hospitalized with varicella infection during the study period in the region 
. In addition, the study included children hospitalized for varicella infection prior to the introduction of universal VZV vaccination in 2004. Hence, any changes observed in the epidemiological trends of varicella infection cannot be attributed to the introduction of the VZV universal vaccination. However, due to the retrospective nature of the study design applied, the etiological association between climatic changes and varicella infection cannot be conclusively established. Moreover, the potential confounding effects of socioeconomic factors upon the association of interest could also not be evaluated due to the retrospective study design applied. Finally, the present study cannot account for varicella infection cases contracted through direct cutaneous contact, rather than through the transmission via aerosolized droplets. Additional longitudinal studies are necessary to evaluate the interactive effects between demographic, climatic, and epidemiological changes, respectively, of other airborne viral diseases upon infection rates among children in temperate regions.
In conclusion, in a temperate Mediterranean region where significant variations in seasonality occurred during the pre-licensure period for the varicella vaccine (1982–2003), the occurrence of pediatric hospitalized varicella cases significantly increased during the summer and decreased during the autumn seasons. The observed epidemiological changes in the time trends of pediatric hospitalized varicella cases may be attributed to climatic changes in the region. It is hypothesized that time trends in the epidemiology of pediatric hospitalized cases for other infectious diseases which are similarly transmitted through indirect airborne transmission, such as influenza 
, may have also been affected by modifications in climatic variables 
. Therefore, public health interventions targeted at diminishing such infectious diseases among pediatric populations in the region should also account for the potential notable effects of modification of climatic variables upon the epidemiology of disease attributable hospitalizations