Journal of the Medical Association of Thailand Vol 97, No 2:FEBRUARY 2014 (SUPPL. 2) 0125-2208 97 2 2014 Dec Incidence and Risk factors of Blastocystis infection in Orphans at the Babies’ Home, Nonthaburi Province, Thailand 52 EN Jitrada Boondit Duangnate Pipatsatitpong Mathirut Mungthin Paanjit Taamasri Peerapan Tan-ariya Tawee Naaglor Saovanee Leelayoova Original Article A retrospective cohort study of Blastocystis sp. was conducted in orphans aged less than 5 years and their childcare workers at Babies’ Home, Nonthaburi Province, Thailand. A base line survey was conducted in December 2009 and a follow-up survey was conducted in April 2010. A total of 336 and 331 stool samples were collected. Blastocystis infection was examined using short-term in vitro cultivation in Jones’s medium supplemented with 10% fetal calf serum. To analyze subtypes of Blastocystis sp., PCR-RFLP of the small subunit ribosomal RNA gene was performed. The prevalence of Blastocystis infection in December 2009 and April 2010 were 8.1% and 13.3%, respectively. The incidence rate of Blastocystis infection was 1.6/100 person-months. Subtype analysis of Blastocystis sp. in December 2009 and in April 2010 showed that subtype 3 was the most predominant (76% and 76%), followed by subtype 1 (16% and 20%), and unidentified subtype (8% and 4%), respectively. Subtype 3 is of human origin, thus person-to-person transmission is considered a major route of Blastocystis infection in this population. Person-to-person transmission of Blastocystis infection in orphans living in the same house had been proposed, thus the prevalence and incidence of Blastocystis infection could be used to reflect the hygienic condition in the orphanage. Infection prevention and control practice can be effectively implemented. Blastocystis infection Blastocystis sp. Subtype Orphans