Isolation of Cryptococcus neoformans from pigeon (Columba livia) droppings in Mexico City.

To determine the ecological and epidemiological significance of pigeon excrement in cryptococcosis in Mexico City, 251 samples of pigeon droppings were studied. These were collected from houses, public buildings, churches, parks and pigeon nests. Each sample was suspended 1:10 in isotonic saline solution and then cultured in Staib medium. Identification of Cryptococcus neoformans was performed based on the development of brown-coloured colonies and the presence of encapsulated yeasts. Of 251 samples, 52 (20.7%) were positive for Cr. neoformans. The highest frequency was observed in droppings from public buildings (31.2%), followed by churches (22.0%) and houses (13.3%). No significant differences in isolation frequency were observed between fresh or dried excrement. All isolates obtained were Cr. neoformans var. neoformans. As in other studies on Cr. neoformans from pigeons, performed in other countries, these frequency data are considered 'normal'. The results, however, accentuate the potential risk of cryptococcosis acquisition, especially now that cryptococcosis frequency is increasing in Mexico, mainly in AIDS patients.