Endemic diseases measured by prevalence of IgG antibodies by ELISA all showed remarkably stable overall prevalences over a study period of 3 years. This however does not mean that incidence is low or absent. Observed transition from the state of being positive for a disease to the state of being negative and vice versa suggested fairly high incidence rates (and rates of waning antibodies) for all 19 disease agents tested for. In spite of this dynamic situation Markov Chain simulations indicate that a steady prevalence is reached in a fairly short time. Markov Chain simulations may also be useful in elucidating seasonal changes in prevalence.
prevalence; Markov Chain; México; ELISA
