[Measles and rubella in the city of Carbonia]

The Italian "Consiglio Sanitario Nazionale", in the report about the years 1984 to 1986, emphasized the role of immunization programmes in order to reduce the scale of epidemics of measles and rubella. In this research work self-administered questionnaires have been used to study the incidence of measles and rubella in the infant population (1990 students) of the city of Carbonia (30000 inhabitants). Data analysis has been carried out by an exponential model. The force of infection "h" is the per capita rate at which susceptible individuals acquire infection. The force of infection represents the totality of a variety of factors that determine transmission of infection. For measles and rubella, the force of infection appears to increase linearly by age for people under 7-8 years old. In spite of this, as far as our study where the children are 3-10 years old is concerned, we can take it to be a constant. Under these conditions the proportion (y) of susceptibles at age x is given by y = exp (-(a + hx)). The equation may be modified to make calculations easier. We can write: ln y = z. The parameters "a" and "h" and the estimated values can be determined using linear regression. We can also calculate the 95% percent confidence intervals. The magnitude of both the coefficients of determination (R2 = 0.976 for measles; R2 = 0.932 for rubella) is suggestive for a good fitting. The force of infection is much higher for measles (h = 0.186 + 0.029) than for rubella (h = 0.035 + 0.009).