Leprosy in Portugal 1946-80: epidemiologic patterns observed during declining incidence rates.

Compulsory notification of leprosy in Portugal formed the basis for the establishment of a national patient registry used in an epidemiological study. Highest incidence rates were observed in the coastal counties in the middle of Portugal and particularly in the municipalities with a high annual rainfall. Peak incidence rates in males was observed at the age of 25-29 years against 50-59 in females. A continuous and increasing decline in incidence rates was observed throughout the observation period, 1946-80. Towards the end of the period the slopes of the incidence curves seemed to be identical with those observed in other countries where leprosy has previously been eradicated. This is consistent with the notion that towards the end of an endemic situation no new transmission of the disease occurs, and the incidence curve takes the shape of the right part of the distribution of incubation periods which apparently is uniform in leprosy, irrespective of time and place. The pattern observed in other areas during declining incidence rates, of an increase in age at onset by year of onset together with a lack of increase in age at onset by year of birth was confirmed by the Portuguese data, also consistent with a break in the transmission of the disease a long time before the final termination of the endemic situation.