RESUMEN
Observation of acid fast C. cavetanensis oocysts were proved in a sputum sample of a 45 years-old male HIV negative patient who was admitted to Chest Hospital due to loss of weight, cough with expectoration of purulent sputum and dyspnea. The radiological picture suggested active pulmonary tuberculosis (TB). Sputum samples which were positive for acid fast bacilli as proved by Ziehl-Neelsen stain technique showed large (8-10 microm) spherical acid-fast C. cayetanensis oocysts and their identify was confirmed by molecular techniques (Nested PCR). The patient was successfully treated for TB since 4 years. However, this was the second time to report C. cayetanensis oocysts in human sputum. The first one was in Argentina. So, C. cayetanensis is a new respiratory system pathogen which must be considered in the differential diagnosis.