I'm trying to model count data with both a Poisson regression model and a Negative binomial model. These counts are referred to the spread of a disease in each spatial unit area (I have 110 obs). I work with R or SAS and I would like to do something like a SAR model but referred to counts (I need non-negative fitted values, of course). How can I account for spatial dependence? The only thing I can reasonably do is to use a SLX model (SAS allows you to do that) and comment the regression coefficients of the neighborhood. But is this a "real" spatial dependence? Which software can handle such (rare?) models?