Biogeographical origin and varicella risk in the adult immigration population in Catalonia, Spain (2004-2006)

Immigrants to the European Union may have a higher susceptibility to varicella-zoster virus primo-infection than the indigenous population. There is no evidence as yet that this is caused by genetic or social factors. Therefore, susceptibility could be due to a lesser transmission of the virus in their ecosystems of origin. A multicentre observational study was performed from July 2004 to June 2006 in four primary healthcare centres in Catalonia, Spain, monitoring varicella incidences and comparing standardised incidence rates and standardised rate ratios among different populations classified according to their biogeographical origin (holarctic, Asian paleotropical, African paleotropical or neotropical). Overall, 516 varicella cases were recorded. The standardised incidence rates per 1,000 inhabitants per year were: holarctic: 2.17 (95% confidence interval (CI): 1.95-2.39); autochthonous 2.26 (95% CI: 2.03-2.49); immigrants 3.59 (95% CI: 2.92-4.26); neotropical 4.50 (95% CI: 3.28-5.71); non-holarctic 5.38 (95% CI: 4.27-6.14); Asian paleotropical 7.03 (95% CI: 4.77-9.28); and African paleotropical 7.05 (95% CI: 1.12-23.58). The difference to the autochthonous population was greatest in immigrants of neotropical origin (standardised rate ratio = 2.07 (95% CI: 1.61-2.64) or 4.5 excess cases per 1,000 inhabitants per year) and Asian paleotropical origin (standardised rate ratio = 3.24 (95% CI: 2.47-4.11) or 9.6 excess cases per 1,000 inhabitants per year). Biogeographical origin may therefore account for the vulnerability of certain immigrant populations to varicella, in particular those from Asian paleotropical (Indostan and Southest Asia) and neotropical (South America and the Caribbean) ecosystems. Vaccination of immigrants at high risk (fertile women, healthcare workers) could be recommendable.